Q

quaternium-15 (AVERAGE)

Formaldehyde-releasing preservative used in cosmetics. It can be a skin sensitizer, as can all preservatives, although quaternium-15’s ability to sensitize skin is very low if the amount in a product is less than 0.2%.[693]

quercetin (BEST)

Bioflavonoid ingredient from plants. Quercetin occurs naturally in red wine, tea, onions, kale, tomatoes, berries, and many other fruits and vegetables, with the highest concentrations found in the leaves and skins. It functions as an antioxidant, anti-inflammatory agent, and skin-healing ingredient, likely owing to the stimulating effect it has on the immune system, of which skin is our body’s first line of defense. Quercetin is present in some herbal ingredients, too, including St. John’s wort and Ginkgo biloba.

In terms of skincare, research has shown that a lipid-based delivery system is optimal for quercetin to exert antioxidant benefits.[694] Even more exciting, this type of formula provides an initial burst of quercetin followed by sustained release over a 24-hour period. When quercetin is mixed with silicone and lipids, the intake is greater, as confirmed by testing on human skin.[695]

More good news on the skincare front: Quercetin can help defend skin from UVB-related damage, reduce the production of an elastin-degrading enzyme, and help heal and improve the appearance of scars.[696,697,698]

R

resveratrol (BEST)

Potent polyphenolic antioxidant abundant in red grapes and, therefore, in red wine. Resveratrol has been reported in numerous studies to be one of the most potent natural chemopreventive agents for inhibiting the cellular processes associated with tumor development, including initiation, promotion, and progression. It also has significant anti-inflammatory properties and seems to have a stimulating and protective effect on glutathione, the body’s master antioxidant.[699,700,701,702] Conversely, there’s also research showing it to be associated with cell death when applied in pure doses directly to skin cells that are then exposed to UV radiation. Of course, this has nothing to do with how resveratrol is used in skincare products, but it’s an interesting example of how more is not necessarily better when it comes to skincare ingredients!

retinoids (BEST)

Large group of over 2,500 chemicals related to vitamin A. Topical, over-the-counter retinoids include retinol, retinyl palmitate, retinaldehyde, and retinyl linoleate, among others. Prescription retinoids include tretinoin (Renova, Retin-A), adapalene (Differin), and tazarotene (Tazorac). Other retinoid chemicals include beta-carotene and various carotenoids found in brightly colored and dark green fruits and vegetables.[19,92,95,96]

When applied topically, retinoids function in multiple ways. Primarily, they work as cell-communicating ingredients, essentially connecting with a receptor site on a skin cell and “telling” it to behave in a more normal and healthier manner. Retinoids have benefits for more than 125 different skin issues, from acne to psoriasis to wrinkles and other signs of sun damage. They can improve, to some extent, how new skin cells are formed and how they behave as they mature (differentiate) and make their way to the skin surface.

Tolerability can be an issue with all retinoids, with the prescription forms more likely to cause side effects than over-the-counter retinol products. The most common side effects from topical application of retinoids include irritation, flaking skin, and redness (sometimes resembling and/or feeling like sunburn, with skin being tender to the touch).[95,96] The side effects tend to appear within 2–4 days from the time you apply the retinoid. In most cases, they subside within a few weeks as your skin adjusts; however, there will always be some people whose skin is simply intolerant of retinoids.

It’s important to avoid applying too much of any retinoid product; more isn’t necessarily better and can often make the potential side effects an unwelcome reality. For example, the directions for prescription retinoid creams state to apply a pea-size amount, which is plenty. Applying more per use won’t get you better or faster results, but it can increase the chances of unwanted side effects.

Research has shown that varying strengths of retinol and prescription retinoids are beneficial; with any type of retinoid, the “if a little is good, more must be better” mentality can backfire. Some people’s skin can tolerate higher amounts of retinoids, but it’s always best to begin with the lower strength to see how your skin responds and then increase the concentration if results are positive. It’s also fine to alternate between lower- and higher-strength retinoid products; for example, one night you can apply an over-the-counter retinol product, and the next evening apply a prescription retinoid.[19,92,95,96]

retinol (BEST)

Name for the entire vitamin A molecule. Retinol has value for skin on several fronts: It’s a cell-communicating ingredient and an antioxidant. Skin cells have a receptor site that’s very accepting of retinoic acid, which is a component of retinol. This relationship between retinoic acid and skin cells allows for a type of communication in which the cell is told to function normally (that is, not like a damaged or older cell), and it can, to some extent, conform to that request. That’s one of the reasons retinol is an exciting anti-aging ingredient. Retinol cannot communicate with a cell until the retinol is broken down into retinoic acid.[5,19,20]

Retinol helps skin cells create better, healthier skin cells, provides antioxidant support, and increases the amount of substances that enhance skin’s structural elements. Packaging is still a key issue, so any container that lets in air (like jar packaging) or sunlight (clear containers) just won’t cut it, which applies to most state-of-the-art skincare ingredients. Lots of retinol products come in unacceptable packaging; these should be avoided because the retinol will most likely be (or quickly become) ineffective.[5,19,20]

Many consumers are concerned about the percentage of retinol in anti-aging products such as serums or moisturizers. Although the percentage can make a difference (especially if it’s too low), it is not helpful in understanding how a retinol product will benefit your skin. Far more important is the delivery system, packaging, and the other ingredients present with the retinol. Using a product with a range of anti-aging ingredients plus retinol is far more valuable for skin than using a product with only a supposedly high percentage of retinol. Skin is the largest organ of the body and needs far more than any one ingredient can provide. It doesn’t make sense to fixate on the percentage of retinol when so many other elements are also important.[5,19,20]

Because retinol is one of the ingredients known to help improve skin structure, it has some value in anti-cellulite products. Of all the ingredients to look for in a cellulite product, this should be at the top of the list. However, most cellulite products contain only teeny amounts of retinol (at best) and they are often in packaging that won’t keep this air-sensitive ingredient stable.

retinyl palmitate (BEST)

Combination of retinol (pure vitamin A) and palmitic acid. Research has shown it to be effective as an antioxidant and skin-cell regulator.[703] Is retinyl palmitate safe for skin? We discuss this in depth in Chapter 14, under the question of whether or not sunscreen ingredients cause cancer.

retinyl retinoate (BEST)

Synthetic, “new generation” retinoid with research showing its usefulness for wrinkles, acne, and hyaluronic acid synthesis in skin. Retinyl retinoate has been shown, in limited but promising research (most coming from the same team of Korea-based researchers), to be less irritating than retinoic acid (prescription-strength) and over-the-counter retinol. Retinyl retinoate may be less irritating than pure retinol because of its slower conversion in skin to retinoic acid. However, when it comes to irritation from retinol, there’s much that can be done using time-release delivery systems and ingredient additions to maximize its benefits to skin while minimizing, if not eliminating, its risk of irritation (so-called “retinol dermatitis”).[723,724,725]

Although there’s reason to consider retinyl retinoate if your skin seems intolerant of retinol and prescription retinoids, it shouldn’t be construed as better or safer for skin than over-the-counter products that contain retinol or other types of cosmetic retinoids.[704,705,706]

rice bran oil (GOOD)

Emollient oil similar to other non-fragrant plant oils. Research has not shown that it has any superior benefit for skin.

Rosa damascena oil (POOR)

Oil of a very fragrant pink rose used as fragrance in cosmetics. Extensive research has shown it has mixed benefits. In the pro column, inhaling this flower’s scent seems to have relaxing, blood pressure–lowering benefits and the plant’s petals contain anti-inflammatory and antioxidant compounds that can benefit skin.[707]

On the flipside, the numerous chemicals that create this rose’s distinctive fragrance pose a risk of irritation and allergic contact dermatitis.[707]

rose flower oil (POOR)

Fragrant, volatile oil that can be a skin irritant and sensitizer. There’s no research showing this has any benefit for skin, although components of rose can have anti-inflammatory and antioxidant effects on skin.[707] The trick is to get those ingredients onto your skin without exposing your skin to the fragrant components that other research has shown can be irritating to skin.

rosehip oil (GOOD)

Non-fragrant emollient plant oil that has antioxidant properties.[708,709]

rosemary extract (AVERAGE)

Extract that can have antioxidant benefit for skin, but its aromatic components can cause irritation or sensitizing reactions.[452,710] However, in most skincare products the amount of rosemary extract is unlikely to be a risk, and rosemary extract is much less of a problem for skin than rosemary oil because the extract usually doesn’t contain much, if any, of rosemary oil’s fragrance components.

rosemary oil (POOR)

Fragrant plant oil derived from rosemary (Latin name Rosmarinus officinalis). This ingredient is used primarily as a fragrance in cosmetics, but the volatile chemicals that give it its fragrance (camphor is among them) are also capable of causing irritation when applied to skin. Research has shown that rosemary has antifungal, antibacterial, and antioxidant benefits; however, because many other ingredients provide these benefits without the risk of irritation presented by rosemary oil, there’s no compelling reason to apply it. If you enjoy the scent, it’s fine to inhale, such as from scented candles.[711,712,713]

rosewood oil (POOR)

Fragrant plant oil with a spicy-sweet scent, also known as bois de rose. Extracted from wood chips from a species of evergreen tree, rosewood oil contains several volatile fragrance chemicals, including camphene, geranial, geraniol, limonene, linalool, myrcene, and neral. Rosewood oil is used chiefly as a fragrance and flavoring ingredient; there’s no research pertaining to its benefit for skin, although it does not appear to have toxic properties. Still, it can kill healthy skin cells, even though this effect seems greater on cancerous cells that would otherwise continue to spread.[714,715]

S

saccharide isomerate (GOOD)

Good water-binding agent and emollient for skin, and particularly helpful for dry skin because it seems to have the ability to bind to skin’s proteins and to stick around longer than other emollients, which are more easily washed away.

safflower seed oil (BEST)

Emollient plant oil similar to all non-fragrant plant oils. Safflower seed oil contains beneficial fatty acids, primarily linolenic acid, that can help repair skin’s barrier and that are of particular value to those with dry skin.

salicylic acid (BEST)

Also called beta hydroxy acid (BHA), this multifunctional ingredient addresses many of the systemic causes of acne.[716] For decades, dermatologists have been prescribing salicylic acid as an exceedingly effective keratolytic (exfoliant), but it’s also an anti-irritant because it is a derivative of aspirin (both are salicylates—aspirin’s technical name is acetylsalicylic acid), and so it also functions as an anti-inflammatory.[31,33]

Another notable aspect of salicylic acid for treating breakouts is that it has antimicrobial properties.[69] It has the ability to penetrate into the pore lining and exfoliate inside the pore as well as on the surface of skin, which makes it effective for reducing breakouts, including blackheads and whiteheads.[31,33]

It is also well that documented that salicylic acid can improve skin thickness, barrier function, and collagen production.[16,31,33] As an exfoliant, in concentrations of 8% to 12%, it is effective in medications to remove warts. In concentrations of 0.5% to 2%, it is far gentler, and, much like AHAs, can exfoliate the surface of skin.

sandalwood oil (POOR)

Fragrant oil (Latin name Santalum album) that can cause skin irritation or allergic reactions. One animal study showed it to have antitumor properties.[717] Sandalwood oil is a must to avoid if you have extra-sensitive skin or if you normally react to fragrance.

SD alcohol (POOR)

See alcohol.

sea buckthorn (GOOD)

Berry extract that grows on a shrub-like tree. The fruit of this plant contains malic and acetic acids (AHA-like ingredients that give the fruit an astringent, acidic taste) as well as beneficial compounds known as flavonoids, plus fatty oils. Sea buckthorn is a rich source of vitamin C, but most of it is lost when the fruit is processed for production (which includes manufacture for use in cosmetics products).

Sea buckthorn is believed to have several topical benefits, including for acne, but the research to support such claims is lacking. More convincing is the research pertaining to sea buckthorn’s ability to help skin heal when applied to wounds, and it does appear to have some antioxidant ability.[718,719]

Research has also shown that oral consumption of sea buckthorn can help reduce topical symptoms of UV damage by controlling the rate of collagen degradation and by increasing the activity of superoxide dismutase, a naturally occurring antioxidant that helps skin repair damage.[720]

sesame oil (GOOD)

Emollient oil (Latin name Sesamum indicum) similar to other non-fragrant plant oils. Despite the similarity to other plant oils, sesame oil isn’t quite as impressive as some others we’ve rated higher.

shea butter (BEST)

Plant lipid, extracted from the karite tree, that is used as an emollient in cosmetics. Shea butter is a rich source of antioxidants, including epicatechin gallate, gallocatechin, epigallocatechin, gallocatechin gallate, and epigallocatechin gallate, as well as quercetin.[721]

silica (GOOD)

Mineral found abundantly in sandstone, clay, and granite, as well as in parts of plants and animals. It’s the principal ingredient of glass. In cosmetics it is used as an absorbent powder and thickening agent.

silica dimethyl silylate (GOOD)

Used as a slip and suspending agent in cosmetics.

silicone (GOOD)

Substance derived from silica (sand is a silica). The unique fluid properties of silicone give it a great deal of slip, and in its various forms it can feel like silk on skin, impart emollience, and be a water-binding agent that holds up well, even when skin becomes wet. In other forms, it’s used extensively for wound healing and for improving the appearance of scars.[722]

There are numerous forms of silicones used in cosmetic products, particularly leave-on skincare products and all manner of hair-care products. Common forms of silicone are cyclopentasiloxane and cyclohexasiloxane; other forms include various types of dimethicone and phenyl trimethicone.

Claims that silicones in any form cause or worsen acne have not been substantiated in published research, nor have reports that silicones are irritating to or “suffocate” skin. Almost all of these claims are either myths or based on anecdotal evidence, which isn’t the best way to determine the safety or efficacy of any cosmetic ingredient. How do we know that silicones don’t suffocate skin? Because of their molecular properties they are at the same time porous and resistant to air. Think of silicones in a skincare formula like the covering of a tea bag. When you steep the tea bag in water; the tea and all of its antioxidant properties are released.

Silicones remain on the surface of your skin and the other ingredients it’s mixed with “steep” through. All ingredients must be suspended in some base formula; some of the ingredients remain on the surface, some are absorbed. The intent is for the “actives” to get through. Think of how many topical medications are suspended in petrolatum or mineral oil and the active ingredients absolutely get through, and petrolatum is far more effective at preventing moisture loss than silicones are.

Moreover, the molecular structure of commonly used silicones makes it impossible for them to suffocate skin (not to mention skin doesn’t breathe). The unique molecular structure of silicones (large molecules with wide spaces between each molecule) allows them to form a permeable barrier and also explains why silicones rarely feel heavy or occlusive, although they offer protection against moisture loss.[723]

Interestingly, silicone has been shown to be helpful for offsetting dryness and flaking from common anti-acne active ingredients such as benzoyl peroxide and topical antibiotics.[724] Also, silicones are sometimes used as fillers to improve the appearance of acne scars, which certainly wouldn’t be the case if silicone were a pore-clogging ingredient.[725] Perhaps the most telling reason why silicones do not clog pores and cause acne (or blackheads) is because, from a chemistry standpoint, most silicones are volatile. That means their initially viscous (thick) texture evaporates quickly and does not penetrate the pore lining where acne is formed. Instead, they help ensure the even application of other ingredients and leave behind a silky, almost imperceptible feel that noticeably enhances skin’s texture and appearance—without irritation.

slip agent (GOOD)

Term used to describe a range of ingredients that help other ingredients spread over skin and penetrate into it. Slip agents also have humectant properties. Slip agents include butylene glycol, glycerin, polysorbates, and propylene glycol, to name a few. They are as basic to the world of skincare as water.

sodium acrylate acryloyldimethyl taurate copolymer (GOOD)

Synthetic polymer used as a stabilizing and suspending agent and as a thickening agent. See polymer.

sodium ascorbyl phosphate (BEST)

Stable, water-soluble form of vitamin C that functions as an antioxidant.[379,611] There’s limited, but promising, research demonstrating that concentrations above 1% have antibacterial action against acne-causing bacteria, while concentrations of 5% reduce the inflammatory response related to acne.[111,726]

This form of vitamin C is also potentially effective for lightening skin discolorations, although there isn’t much research supporting its use for this purpose over other forms of vitamin C.

sodium benzoate (GOOD)

Salt of benzoic acid used as a preservative. The benzoic acid portion of this ingredient conveys some amount of preservative benefit, most notably against fungi.

sodium C14-16 olefin sulfonate (POOR)

Used primarily as a detergent cleansing agent, but is potentially drying and irritating for skin. Can be derived from coconut. It’s tricky to include in formulas due to stability issues, but it does produce copious foam. Secondary surfactants can be used with this cleansing agent to minimize its negative impact on skin, but why not just use a cleanser that contains gentler cleansing agents? All skin types do better with gentle cleansing agents, and there are plenty of options in that regard, so no need to settle for one that contains this potentially problematic cleansing agent.

sodium chloride (GOOD)

More popularly known as common table salt. Used primarily as a binding agent in skincare products and occasionally as an abrasive in scrub products. Perhaps the most common use of sodium chloride in cosmetics is as a thickening agent. Salt is commonly used to thicken the water (also known as aqueous) phase of shampoos, body washes, and non-soap facial cleansers.

sodium cocoamphoacetate (GOOD)

Gentle cleansing agent derived from coconut fatty acids. It functions as a cleansing agent and can also have mild conditioning properties. It has a slight tendency to foam during use.

sodium cocoate (POOR)

Cleansing agent used primarily in soaps and bar cleansers. It can be drying and irritating for skin.

sodium cocoyl glutamate (GOOD)

Cleansing agent derived from coconut oil. This ingredient is also used to help soften (remove excess minerals from) hard water.

sodium cocoyl isethionate (GOOD)

Derived from coconut, a mild detergent cleansing agent and the chief ingredient in non-soap Dove Beauty Bar.

sodium dehydroacetate (GOOD)

Organic salt used as a preservative.

sodium hyaluronate (BEST)

Salt form of skin-identical ingredient hyaluronic acid; considered more bioavailable to skin than pure hyaluronic acid. See hyaluronic acid.

sodium hydroxide (AVERAGE)

Also known as lye, sodium hydroxide is a highly alkaline ingredient used in small amounts in cosmetics to establish and hold the pH of a product. Also used as a cleansing agent in some cleansers. In high concentrations, it’s a significant skin irritant.[727]

sodium laureth sulfate (GOOD)

Used primarily as a detergent cleansing agent. Can be derived from coconut. It’s considered gentle and effective as typically used in cosmetics products (typically facial or body cleansers and shampoos). Despite the name similarity, sodium laureth sulfate is NOT the same as sodium lauryl sulfate. The former is a milder cleansing agent due to a higher amount and different chemical structure of the fatty alcohols required to manufacture this cleansing agent. The safety of sodium laureth sulfate has been reviewed by numerous industry experts and deemed safe as used.[360,728]

sodium lauroamphoacetate (GOOD)

Mild surfactant (cleansing agent) also used as a lather agent.

sodium lauryl sulfate (POOR)

Versatile ingredient composed of several non-volatile alcohols. Functions primarily as a surfactant, but can also be used as a skin-conditioning agent, emulsifier, and solvent. Sodium lauryl sulfate (SLS) is one of the most irritating cleansing agents used in skincare products. In fact, it’s considered a standard comparison substance for measuring the skin irritancy of other ingredients. Thus, in scientific studies, when they want to establish whether or not an ingredient is problematic for skin, they compare its effect to the effect of SLS.[360]

In amounts of 2% to 5%, sodium lauryl sulfate can cause allergic or sensitizing reactions for many people.[729,730] Despite the irritancy issue, it is not the same as the dire and erroneous warnings floating around the web about this ingredient.

sodium methyl cocoyl taurate (GOOD)

Mild surfactant derived from coconut; often used in cleansers when the desired effect is a creamy foam.

sodium palmate (POOR)

Soap ingredient created by the salts of acids derived from palm oil. May be naturally derived or synthetic. As a soap ingredient, it can be drying and is typically formulated at an alkaline pH, which disrupts skin’s barrier function and can increase harmful bacteria on skin.

sodium PCA (BEST)

Natural component of skin, PCA (pyrrolidone carboxylic acid) is also a very good water-binding agent. Sodium PCA also functions as a skin-repairing ingredient.[155]

sodium polyacrylate (GOOD)

Versatile, synthetic polymer used as a film-forming agent, stabilizer, absorbent, thickening agent, and emollient.

solvent (GOOD)

Large group of ingredients, including water, that are used to dissolve or break down other ingredients. Solvents are also used to degrease skin and to remove sebum.

sorbic acid (GOOD)

Preservative derived from mountain ash berries or manufactured synthetically. Sorbic acid is used in many products, including several foods and even in contact lens solutions. A study of contact sensitization to preservatives among 514 volunteers with eczema showed that sorbic acid caused a reaction in only 0.6% of participants. In contrast, many other preservatives had much higher rates of negative reactions, upwards of 13.6%.[731]

sorbitan stearate (GOOD)

Emulsifier used to thicken and stabilize cosmetics formulations. See emulsifier.

soy extract (BEST)

Potent antioxidant and anti-inflammatory agent for skin.[732] Soy is one of many phytochemicals (phyto = plant) that are biologically active against free radicals. Soy extract’s increasing use in anti-aging products is largely due to studies showing that its antioxidant genistein (a component of soy) has a collagen-stimulating effect and that various compounds in soy influence skin thickness and elasticity.[733,734]

Researchers have also looked at Bifidobacterium-fermented soy milk extracts. On mouse skin and in human skin fibroblasts (lab cultured), this bacteria-modified form of soy was shown to stimulate the production of hyaluronic acid in skin. This was due to the amount of genistein released during the fermentation process.[734,735]

Soy extract has been shown to help reduce the effects of UVB exposure on human skin cells.[736,737]

Research hasn’t shown that soy extract or soy oil has estrogenic effects when applied to skin, as it can when taken orally.[738]

soy oil (BEST)

Emollient oil similar to all non-fragrant plant oils.

squalene (BEST)

Oil derived from shark liver or from plants (usually olives) and sebum. Its derivative squalane is a natural component of skin and a good emollient that has antioxidant and immune-stimulating properties.[739,740]

St. John’s wort (GOOD)

Plant that contains several components that can cause a negative reaction on skin in the presence of sunlight. Any product that contains St. John’s wort should be followed by application of a broad-spectrum sunscreen.[741]

St. John’s wort’s association with improving depression when taken as an oral supplement is unrelated to its topical impact on skin. However, it does have potent antioxidant properties.[742]

In terms of skin healing, research has shown that St. John’s wort enhances the process while minimizing pain, making it a suitable option for helping to minimize the formation and ultimate appearance of scars. St. John’s wort also has antifungal and antibacterial activity.[743]

stearic acid (GOOD)

Fatty acid used as an emollient and emulsifier. See emollient; emulsifier.

stearyl alcohol (GOOD)

Fatty alcohol used as an emollient and to help keep other ingredients intact in a formulation. Not to be confused with the drying, irritating types of alcohol such as SD alcohol or denatured alcohol.

stem cells (AVERAGE)

Cells in animals and in plants that are capable of becoming any other type of cell in that organism and then reproducing more of those cells. Despite the fact that stem cell research is in its infancy, many cosmetics companies claim they are successfully using plant-based or human-derived stem cells in their anti-aging products. The claims run the gamut, from reducing wrinkles to repairing elastin to regenerating cells, so the temptation for consumers to try these products is intense.

The truth is that stem cells in skincare products do not work as claimed; they simply cannot deliver the promised results. In fact, they likely have no effect at all because stem cells must be alive to function as stem cells, and by the time these delicate cells are added to skincare products, they are long since dead and, therefore, useless. Actually, it’s a good thing that stem cells in skincare products can’t work as claimed, given that studies have revealed that they pose a potential risk of cancer.

Plant stem cells, such as those derived from apples, melons, and rice, cannot stimulate stem cells in human skin; however, because they are derived from plants they likely have antioxidant properties. That’s good, but it’s not worth the extra cost that often accompanies products that contain plant stem cells. It’s also a plus that plant stem cells can’t work as stem cells in skincare products; after all, you don’t want your skin to absorb cells that can grow into apples or watermelons!

There are also claims that because a plant’s stem cells allow a plant to repair itself or to survive in harsh climates, these benefits can be passed on to human skin. How a plant functions in nature is completely unrelated to how human skin functions, and these claims are completely without substantiation. It doesn’t matter how well the plant survives in the desert, no matter how you slather such products on your skin, you still won’t survive long without ample water, shade, clothing, and other skin-protective elements.

Another twist on the stem cell issue is that cosmetics companies are claiming they have taken components (such as peptides) out of the plant stem cells and made them stable so they will work as stem cells would or that they will influence the adult stem cells naturally present in skin. In terms of these modified ingredients working like stem cells, this theory doesn’t make any sense because stem cells must be complete and intact to function normally. Using peptides or other ingredients to influence adult stem cells in skin is something that’s being explored, but to date scientists are still trying to determine how that would work and how it could be done safely. For now, companies claiming they’ve isolated substances or extracts from stem cells and made them stable are most likely not telling the whole story. Currently, there’s no published, peer-reviewed research showing these stem cell extracts can affect stem cells in human skin.

sulfates (GOOD)

In cosmetics, used mainly as cleansing agents in skincare and hair-care products; they include sodium lauryl sulfate, ammonium lauryl sulfate, and sodium laureth sulfate. Many consumers are scared of sulfates in their cosmetics products because of widespread misinformation. Sulfates are not a problem, but once organizations and companies build up fears among consumers about certain cosmetics ingredients there’s almost no going back, the damage is done.[360,744,745,746]

In reality there’s absolutely no research showing that sulfates are a problem in skincare or hair-care products, other than causing irritation, but that is also true for the sulfate-free cleansing agents that some cosmetics companies advertise and sell. And, whether or not a cleansing agent will cause irritation depends on the amount of sulfate and on other ingredients present in a specific formula.[360,744,745,746]

Following are some of the most typical unsupported comments about sulfates:

“Sulfate-free shampoos and cleansers are better for hair and skin.” No research has shown that to be even remotely the case. Sulfates are supposed to be terribly drying and damaging to hair, when in fact they function no differently from the cleansing agents in sulfate-free shampoos. Almost every company that touts the fact that they don’t contain sulfates do use detergent cleansing agents such as sodium lauryl sulfoacetate, disodium laureth sulfosuccinate, sodium lauroyl sarcosinate, cocamidopropyl hydroxysultaine, sodium cocoyl isethionate, cocamidopropylamine oxide, and sodium methyl 2-sulfolaurate. Why those are supposedly any better for skin is never explained, and no research is ever cited—because none exists. Sometimes these companies list those ingredients as being derived from or coming from coconut to make them sound natural and, by association, better for skin—but they all end up being primarily synthetic. That doesn’t make them bad in any way; it’s just that the claims are completely disingenuous. What you need to know is that both the sulfate-free cleansing agents and the sulfate versions can be drying and irritating depending on the formulation and/or your skin’s own reaction. All of these cleansing agents remove oil, built-up skin cells, and the gunk from styling products, which is exactly what a shampoo should do.

“Sulfates cause cancer, cataracts, and kidney and liver failure.” These are perhaps the most frightening of the misguided comments you may have heard, but none of these are supported by research. Even the websites that love to scare you about ingredients conclude there’s no research showing that sulfates in shampoos or cleansers can cause these health problems.

Another website includes a study from the 1980s where a pure sulfate cleansing agent was used in the eyes of rabbits. Not surprisingly, putting a pure sulfate into a rabbit’s eyes caused irritation, but these kinds of studies showed the same thing for mascara (which most women use every day) and would show the same thing for lemon or peppermint. How any of that relates to the amount present in shampoos and to how shampoos are used is just inexplicable thinking. Even more to the point, those who work in the manufacture of pure sulfates have no increased risk of cancer, cataracts, or anything else.

Despite the fact that there is no research showing any association between sulfates and these grave health problems, it still gets mentioned because some sulfates have been found to contain a minute amount of 1,4-Dioxane, which is classified as a probable human carcinogen because of results from animal studies where rats were fed this substance. But ingesting pure 1,4-Dioxane is not the same thing as using it on skin or hair. Keep in mind, not all products containing sulfates contain 1,4-Dioxane and the alternative sulfate-free cleansing products could easily contain 1,4-Dioxane, but that issue is never addressed. Of course, it wouldn’t be because these companies don’t want to scare you away from using their products. They simply want to reinforce the “sulfates are bad, our products are safe” message.

“Sulfates clog pores.” Simply ridiculous! If anything, there’s research showing that when used in appropriate amounts, these cleansing agents clean hair and skin gently and reduce breakouts!

“Sulfates in cleansers are cheap.” This one is true, but so what? Lots of ingredients, both natural and synthetic, are cheap, others are expensive, which has absolutely nothing to do with quality or efficacy. The first ingredient in sulfate-free shampoos is water (about 90% water) and no other cosmetic ingredient is cheaper than that!

“Sulfates are used in floor cleaners and are corrosive.” This can be true, when used in large amounts and when left on surfaces over time, but so what? Salt is used to melt ice on the roadway, but it also rusts cars, which doesn’t make salt bad; it just depends on how much you use and how long you leave it on something. This is also true for the alternative sulfate-free shampoos and cleansers as well; they can also be corrosive over time depending on how much is used and how long it is left on.

“Sulfates can be irritating.” This can absolutely be true, but again, so what? As a general category, sulfates are not irritating when used in appropriate amounts in shampoos and cleansers and the same is true for sulfate-free alternative cleansing agents. All of the research about sulfates being irritating are from patch tests where a concentration is left on skin under a bandage for 24 hours, which is not how a cleanser or shampoo is used. Sodium lauryl sulfate is considered one of the more irritating cleansing agents and we recommend avoiding it when it is high up on the ingredient list, but that’s NOT because it’s a sulfate; rather, it’s because of its interaction with skin.

In summary, not all sulfates are the same, and there are plenty of them that are completely safe and beneficial in skincare and hair-care formulations. More to the point, sulfate-free alternatives can also be extremely drying and irritating when left on skin for long periods of time under occlusion, but that’s not how they are used, either.

sunflower seed oil (BEST)

Non-volatile, non-fragrant plant oil used as an emollient in cosmetics. Sunflower seed oil has the ability to help repair skin’s barrier and reduce inflammation. It’s a rich source of fatty acids skin can use, including linoleic acid, and is excellent for dry skin.[649]

superoxide dismutase (BEST)

Enzyme considered a potent antioxidant in humans.[747,748,749]

surfactant (GOOD)

Short term for surface active agent. Surfactants degrease and emulsify oils and fats and suspend soil, allowing them to be washed away. Surfactants are used in most forms of cleansers and many are considered gentle and effective for most skin types. There are several types of surfactants that can be sensitizing, drying, and irritating for skin. When those are the main ingredients in a facial cleanser, body wash, or shampoo, they should be avoided; the most common among drying, irritating surfactants is sodium lauryl sulfate. The similar-sounding ingredient sodium laureth sulfate is fine.[360,744,745,746]

T

talc (GOOD)

Naturally occurring silicate mineral that is typically the main ingredient in face powders and is also used as an absorbent in skincare products. Extensive research indicates there’s no increased risk of lung cancer when using talc-based products or for those involved in the manufacture of talc products.[750] Although there’s epidemiological evidence that frequent use of pure talc over the female genital area may increase the risk of ovarian cancer.[751,752] However, a study reviewed in Regulatory Toxicology and Pharmacology stated that “Talc is not genotoxic, it is not carcinogenic when injected into ovaries of rats.… There’s no credible evidence of a cancer risk from inhalation of cosmetic talc by humans.”[753]

tangerine oil (POOR)

Fragrant, volatile citrus oil that can be a skin irritant (Latin name Citrus tangerina). Tangerine’s chief irritant potential comes from the fragrance chemical limonene.[754] See limonene.

tea tree oil (GOOD)

Also known as melaleuca, from the name of its native Australian plant source, Melaleuca alternifolia. It has disinfecting properties that have been shown to be effective against the bacteria that cause acne. Tea tree oil also has anti-inflammatory properties and is an antioxidant.[755]

Tea tree oil has some interesting research demonstrating it to be an effective antimicrobial agent. The Journal of Applied Microbiology stated, “The essential oil of Melaleuca alternifolia (tea tree) exhibits broad-spectrum antimicrobial activity. Its mode of action against the Gram-negative bacterium Escherichia coli AG100 , the Gram-positive bacterium Staphylococcus aureus NCTC 8325, and the yeast Candida albicans has been investigated using a range of methods. The ability of tea tree oil to disrupt the permeability barrier of cell membrane structures and the accompanying loss of chemiosmotic control is the most likely source of its lethal action at minimum inhibitory levels.”[756]

In addition, in a randomized, placebo-controlled pilot study of tea tree oil in the treatment of herpes cold sores, tea tree oil was found to have similar degree of activity as 5% acyclovir.[757]

For acne there’s also some credible published information showing it to be effective as a topical disinfectant for killing the bacteria that can cause pimples.[758] However, the crux of the matter for tea tree oil is: How much is needed to have an effect?

The Medical Journal of Australia compared the efficacy of tea tree oil to the efficacy of benzoyl peroxide for the treatment of acne. A study of 119 patients using 5% tea tree oil in a gel base versus 5% benzoyl peroxide lotion was discussed. There were 61 subjects in the benzoyl peroxide group and 58 in the tea tree oil group. The conclusion was that “both treatments were effective in reducing the number of inflamed lesions throughout the trial, with a significantly better result for benzoyl peroxide when compared to the tea tree oil. Skin oiliness was lessened significantly in the benzoyl peroxide group versus the tea tree oil group.” However, while the reduction of breakouts was greater for the benzoyl peroxide group, the side effects of dryness, stinging, and burning were also greater—“79% of the benzoyl peroxide group versus 49% of the tea tree oil group.”[759]

For acne, tea tree oil concentrations of 5% to 10% are recommended. However, the amount present in most skincare products is usually less than 1%; therefore, it is not considered effective for disinfecting. Note that tea tree oil is a fragrant oil whose volatile components of limonene and eucalyptol can cause contact dermatitis on exposure to oxygen. Careful use and storage of tea tree oil is advised.[760,761]

TEA-lauryl sulfate (POOR)

Detergent cleansing agent that’s considered too drying, particularly when it’s the primary cleansing ingredient. While there’s abundant research showing that sodium lauryl sulfate is a sensitizing cleansing agent, there’s no similar supporting research for TEA-lauryl sulfate. However, because the relationship between the two is so close, we recommend against using either of them. The basis for this is a judgment call, made from a desire to protect skin from sensitization; however, there are no specific studies we can cite for this recommendation, although there are those who will understandably disagree with our conclusion.

tetrahexyldecyl ascorbate (BEST)

Stable form of vitamin C that is considered an analogue of L-ascorbic acid. Unlike pure vitamin C (ascorbic acid), tetrahexyldecyl ascorbate is lipid (fat) soluble. Some researchers believe this form of vitamin C has a greater affinity for skin because its fatty acid component helps aid penetration and protect the vitamin C component from rapid oxidation. This form of vitamin C has been shown to stimulate healthy collagen production and reduce wrinkle depth.[112]

tetrasodium EDTA (GOOD)

Chelating agent used to prevent minerals present in formulations from bonding to other ingredients.

thickening agents (GOOD)

Substances that can have a soft to hard wax-like texture or a creamy, emollient feel, and that can be great lubricants. There are literally thousands of ingredients in this category that give each and every lotion, cream, lipstick, foundation, and mascara, as well as other cosmetics products, their distinctive feel and form. The various combinations of thickeners play a large role in whether or not you prefer one product over another.

thyme extract (AVERAGE)

Extract derived from the leaf or flower of the thyme plant. It can have potent antioxidant properties. Its fragrant component can also cause skin irritation, but thyme extract’s beneficial components can benefit skin.[762] Generally speaking, thyme extract should not be one of the chief antioxidants in skincare products; however, in lower amounts and mixed with other antioxidants, it can be a beneficial addition.

thyme oil (POOR)

Plant oil (Latin name Thymus vulgaris) that is a source of potent antioxidants, but its fragrant components (which are part of the oil itself) pose a risk of irritation. For this reason, products with thyme extract are a safer bet in terms of getting the “good” antioxidants from thyme without the volatile fragrance components that, while also being antioxidants, also may cause irritation.[442]

Thyme oil does have medicinal uses because, in concentrations of 3% and above, it has antifungal and antibacterial properties.[763,764] However, in these instances the oil was used short-term to eliminate the fungus and/or kill the problematic bacteria, not every day for (potentially) years as would be the case with a skincare product that contains thyme oil.

Tinosorb (BEST)

In Europe there are two sunscreen ingredients—Tinosorb S (bis-ethylhexyloxyphenol methoxyphenyl triazine) and Tinosorb M (methylene bis-benzotriazolyl tetramethylbutylphenol)—that are approved for sun protection across the entire range of UVA radiation.[627] Whether they are preferred over the other UVA-protecting ingredients used in sunscreens has not been established. At the time this book went to print, neither Tinosorb S nor Tinosorb M had been approved for use in the United States or Canada.

titanium dioxide (BEST)

Inert earth mineral used as a thickening, whitening, lubricating, and sunscreen ingredient in cosmetics. It protects skin from UVA and UVB radiation and is considered to have no risk of skin irritation.[643] Because of its gentleness, titanium dioxide is an excellent sunscreen active for use on sensitive or rosacea-affected skin. It’s also great for use around the eyes, as it is highly unlikely to cause stinging.

Although titanium dioxide is a natural ingredient, pure titanium dioxide in nature is almost always adulterated with potentially harmful contaminants such as lead and iron. Therefore, titanium dioxide is purified via synthetic processes for use in cosmetics and sunscreens.

Titanium dioxide is typically micronized and coated for use in cosmetics products. The micronizing makes this somewhat heavy-feeling ingredient easier to spread on skin, plus a bit more cosmetically elegant. Micronized titanium dioxide also is much more stable and can provide better sun protection than non-micronized titanium dioxide. Micronized titanium dioxide does not penetrate skin so there’s no need to be concerned about it getting into your body. Even when titanium dioxide nanoparticles are used, the molecular size of the substance used to coat the nanoparticles is large enough to prevent them from penetrating beyond the uppermost layers of skin.[289,765] This means you’re getting the sun protection titanium dioxide provides without any risk of it causing harm to skin cells.

The coating process improves application, enhances sun protection, and also prevents the titanium dioxide from interacting with other ingredients in the presence of sunlight, thus enhancing its stability. It not only makes this ingredient much more pleasant to use for sunscreen, but also improves efficacy and eliminates safety concerns. Common examples of ingredients used to coat titanium dioxide are alumina, dimethicone, silica, and trimethoxy capryl silane.

Titanium dioxide as used in sunscreens is commonly modified with other ingredients to ensure efficacy and stability. Examples of what are known as surface modifier ingredients used for titanium dioxide include stearic acid, isostearic acid, polyhydroxystearic acid, and dimethicone/methicone copolymer.

Some websites and doctors maintain that titanium dioxide is inferior to zinc oxide, another mineral sunscreen whose core characteristics are similar to those of titanium dioxide. We’re not sure where the information about titanium dioxide not being a great active sunscreen ingredient came from, but the reality is titanium dioxide is a great broad-spectrum SPF ingredient and is widely used in all manner of sun-protection products. What gets confusing for some consumers is trying to decipher research that ranks sunscreen ingredients by a UV spectrum graph. By most standards, broad-spectrum coverage for any sunscreen ingredient is defined as one that surpasses 360 nanometers (abbreviated as “nm,” this is how the sun’s rays are measured). Titanium dioxide exceeds this range of protection, but depending on whose research you look at, it either performs as well as or slightly below zinc oxide.

Although it’s true that titanium dioxide does not rank as high for UVA protection as zinc oxide, it ends up being a small measurement of difference (think about it like being 10 years old versus 10 years and 3 months old). This is not easily understood in terms of other factors affecting how sunscreen actives perform (such as the base formula), so many, including some dermatologists, assume that zinc oxide is superior to titanium dioxide for UVA protection. When carefully formulated, titanium dioxide provides excellent UVA protection. Its UVA protection peak is lower than that of zinc oxide, but both continue to provide protection throughout the UVA range for the same amount of time.[290,789]

tocopherol (BEST)

See vitamin E.

tocopherol acetate, tocopheryl acetate (BEST)

See vitamin E.

trehalose (GOOD)

Plant sugar that has water-binding properties for skin.

tribehenin (GOOD)

Skin-conditioning agent that’s a mixture of glycerin and behenic acid. Also known as glyceryl tribehenate.

tridecyl stearate (GOOD)

Used in cosmetics as a thickening agent and emollient. See thickening agents; emollient.

tridecyl trimellitate (GOOD)

Used as a skin-conditioning agent and thickening agent. See thickening agents.

triethanolamine (GOOD)

Used in cosmetics as a pH balancer. Like all amines, it has the potential for creating nitrosamines. There’s controversy as to whether or not this poses a real problem for skin, given the low concentrations used in cosmetics and the theory that nitrosamines cannot penetrate skin.[766]

triethoxycaprylylsilane (GOOD)

Silicone that functions as a binding agent and emulsifier.

U

ubiquinone (BEST)

Also known as coenzyme Q10, ubiquinone is a very good antioxidant and anti-inflammatory ingredient when applied topically or consumed orally. In cosmetics, ubiquinone is usually synthetic.

ultramarines (GOOD)

Inorganic pigments (of various colors) permanently listed by the FDA for external use only, including around the eye area.

urea (GOOD)

Component of urine, although synthetic versions are used in cosmetics. In small amounts urea has good water-binding and exfoliating properties for skin; in larger concentrations it can cause inflammation.[767]

V

Vanilla planifolia fruit extract (GOOD)

Extract used primarily as a fragrance and flavoring agent. The vanilla plant is a source of catechins (also known as polyphenols), which have antioxidant activity and serve as anti-inflammatory agents.[768]

vinyl dimethicone/methicone silsesquioxane crosspolymer (GOOD)

Blend of silicone polymers that functions as a thickening agent and texture enhancer. See thickening agents.

vitamin A (BEST)

See retinol.

vitamin B3 (BEST)

See niacinamide.

vitamin B5 (BEST)

See panthenol.

vitamin C (BEST)

See ascorbic acid.

vitamin E (BEST)

One of the most well-known and researched antioxidants, both when taken orally and when used in skincare products. If there were an antioxidant hall of fame, vitamin E would likely be its inaugural member (though do not take that to mean it is the “best” antioxidant—there is no single best, just lots of great options). It’s fat-soluble and available in various forms; the most biologically active form is alpha-tocopherol.

There are eight basic forms of the entire vitamin E molecule, which are either synthetically or naturally derived. The most typical forms are d-alpha-tocopherol, d-alpha-tocopheryl acetate, dl-alpha tocopherol, and dl-alpha tocopheryl acetate. The “d” prefix in front of the “alpha” indicates that the product was derived from natural sources, such as vegetable oils or wheat germ; the “dl” prefix indicates that the vitamin was created from a synthetic base. Research has shown that natural forms of vitamin E are more potent and have a higher retention rate in skin than their synthetic counterparts, but both definitely have antioxidant activity.[769]

What about using pure vitamin E for scars? Low amounts of pure vitamin E can be a helpful addition when mixed with other skin-healing ingredients, but high amounts can be a problem. Research published in Dermatologic Surgery concluded that the “… study shows that there’s no benefit to the cosmetic outcome of scars by applying (pure) vitamin E after skin surgery and that the application of topical vitamin E (such as what you may squeeze from a vitamin E pill) may actually be detrimental to the cosmetic appearance of a scar.” In 90% of the cases in this study, topical vitamin E either had no effect on, or actually worsened the cosmetic appearance of scars.[770] However, as many dermatologists will attest, many patients believe vitamin E prevents or reduces the appearance of scars, thus its usage and anecdotal results continue.[771]

Small amounts of vitamin E can have antioxidant effects without the risk of the contact dermatitis that high amounts present. In that sense, vitamin E can be a helpful addition to skin-healing products.

VP/eicosene copolymer (GOOD)

Film-forming agent often used in water-resistant sunscreen products. It helps the sunscreen adhere better to skin and resist breaking down in water. It does not, however, last for hours, which is why you must reapply even water-resistant sunscreens at regular intervals.

VP/hexadecene copolymer (GOOD)

Synthetic polymer that functions as a binding agent, thickener, and dispersing agent in cosmetics. See polymer.

W

walnut-shell powder (AVERAGE)

Abrasive used in scrub products. Walnut shell powder is not preferred to polyethylene beads in a scrub because it’s impossible to make walnut shell particles smooth, which means the sharp edges can cause microscopic scrapes and tears in skin, damaging its barrier.

water (GOOD)

Most widely used cosmetic ingredient; water is almost always listed first on an ingredient label because it is usually the ingredient with the highest concentration. Yet, despite claims of skin’s need for hydration and claims regarding special types of water, it turns out that water may not be an important ingredient for skin. Only a 10% concentration of water in the outer layer of skin is necessary for softness and pliability in this part of the epidermis.[772] Studies that have compared the water content of dry skin with that of normal or oily skin do not find a statistically significant difference in moisture levels between them.[773]

Further, too much water can be a problem for skin because it can disrupt skin’s intercellular matrix, the substances that keep skin cells bonded to each other. The most significant aspect of skin health is the structural organization of the intercellular lipids and the related materials that keep skin intact and prevent water loss.[774,775,776]

willow bark (GOOD)

Plant extract that contains salicin, a substance that when taken orally is converted by the digestive process to salicylic acid (beta hydroxy acid). The process of converting the salicin in willow bark into salicylic acid requires the presence of enzymes, and is complex. Further, salicin, much like salicylic acid, is stable only under acidic conditions. The likelihood that willow bark in the tiny amount used in cosmetics can mimic the effect of salicylic acid is at best questionable, and in all likelihood impossible. However, willow bark may indeed have some anti-inflammatory benefits for skin because, in this form, it appears to retain its aspirin-like composition.[777]

witch hazel (POOR)

Commonly used plant extract that can have potent antioxidant properties and some anti-irritant properties. However, witch hazel’s high tannin content (tannin is a potent antioxidant) can also make it irritating if used repeatedly on skin because it constricts blood flow. The bark of the witch hazel plant has a higher tannin content than the leaves. Producing witch hazel water by steam distillation removes the tannins, but the plant’s astringent qualities are what most believe give it benefit.[778,779,780]

Alcohol is added during the distillation process, the amount typically being 14–15%.[781] Witch hazel water is distilled from all parts of the plant; therefore, you never know exactly what you’re getting, although the alcohol content remains.

Depending on the form of witch hazel, you’re exposing your skin either to an irritating amount of alcohol (which causes free-radical damage and collagen breakdown) or to tannins, or both. Moreover, witch hazel contains the fragrance chemical eugenol, which is another source of irritation.[782]

See eugenol.

X

xanthan gum (GOOD)

Natural ingredient used as a thickening agent and to stabilize emulsions, which is a general term for mixtures of unlike substances such as oil and water.

Y

yeast (GOOD)

Group of fungi that ferment sugars. Yeast is a source of beta-glucan, which is a good antioxidant. Yeasts are basically fungi that grow as single cells, producing new cells either by budding or fission (splitting). Because it reproduces readily, Saccharomyces cerevisiae is the organism that is most widely used in biotechnology. Nevertheless, some forms of yeast are human pathogens, such as Cryptococcus and Candida albicans.

In relation to skin, there is limited information about how S. cerevisiae may provide a benefit. Live yeast-cell derivatives have been shown to stimulate wound healing, but research about this is scant.[783] Much of what is known about yeast’s effects on skin is theoretical, and concerns yeast’s tissue-repair and protective properties or yeast’s antioxidant properties.[784] As a skincare ingredient yeast has potential, but what its function may be or how it would affect skin is not fully understood.

ylang-ylang (POOR)

Fragrant, volatile oil that can also be a skin irritant and has been a known skin sensitizer since 1971. It presents a bigger risk when used daily rather than intermittently.[785,786]

yogurt (AVERAGE)

There’s no research showing that yogurt is effective when applied topically.

Z

zinc (BEST)

Element that has growing evidence that it can be a significant anti-irritant and antioxidant. It also can have anti-acne benefits when combined with a topical antibiotic such as erythromycin. Taken orally, zinc may have positive effects for wound healing and other health benefits.[787,788,789]

zinc oxide (BEST)

Inert earth mineral used as a thickening, whitening, lubricating, and sunscreen ingredient in cosmetics. Along with titanium dioxide, zinc oxide is considered to have no risk of skin irritation. It can also be an anti-irritant and, potentially, an antioxidant.[790,791]

Nano-sized zinc oxide is not believed to be a safety concern for skin.[289]