CHAPTER 198

Sunlight and Skin Damage

The skin shields the rest of the body from the sun’s rays.

Ultraviolet Light: Ultraviolet (UV) light, although invisible to the human eye, is the component of sunlight that has the most effect on skin. UV light is classified into three types, ultraviolet A (UVA), ultraviolet B (UVB), and ultraviolet C (UVC), depending on its wavelength.

UV light in small amounts is beneficial because it helps the body produce vitamin D. However, larger amounts of UV light damage deoxyribonucleic acid (DNA—the body’s genetic material) and alter the amounts and kinds of chemicals that the skin cells make. These changes are responsible for the damaging effects of UV light, including burning, premature skin aging, wrinkling, and skin cancer. Although UVA penetrates deeper into the skin, UVB is responsible for more of the damaging effects of UV light.

The amount of UV light reaching the earth’s surface is increasing, especially in the northern latitudes. This increase is attributable to depletion of the protective ozone layer high in the atmosphere. Ozone, a naturally occurring chemical, blocks much UV light from reaching the surface of the earth. Chemical reactions between ozone and chlorofluorocarbons (chemicals in refrigerants and spray can propellants) are depleting the amount of ozone in the protective ozone layer. The amount of UV light reaching the earth’s surface also varies depending on other factors. UV light is more intense between 10 AM and 3 PM, in the summer, and at higher altitudes. Smoke and smog filter out much UV light, but UV rays may pass through light clouds, fog, and about 1 foot of clear water.

Actinic Keratoses: Precancerous Growths

Actinic keratoses (solar keratoses) are precancerous growths caused by long-term sun exposure. These growths are usually pink or red and appear as flaky, scaly areas. They may also be light gray or brown and feel hard, rough, or gritty. The surrounding skin often appears thin.

Actinic keratoses usually can be removed by freezing them with liquid nitrogen (cryotherapy). However, if a person has too many growths, a liquid or cream containing fluorouracil may be applied. Often, during such treatment, the skin temporarily looks worse because fluorouracil causes redness, scaling, and burning of the keratoses and of the surrounding sun-damaged skin. A relatively new drug, imiquimod, is useful in treating actinic keratoses because it helps the immune system to recognize and destroy cancerous skin growths.

Natural Protection: The skin undergoes certain changes when exposed to UV light to protect against damage. The epidermis (the skin’s uppermost layer) thickens, blocking UV light. The melanocytes (pigment-producing skin cells) make increased amounts of melanin, which darkens the skin, resulting in a tan. Melanin absorbs the energy of UV light and helps prevent the light from damaging skin cells and penetrating deeper into the tissues.

Sensitivity to sunlight varies according to the amount of melanin in the skin. Darker-skinned people have more melanin and therefore greater protection against the sun’s harmful effects, although they are still vulnerable to some extent. The amount of melanin present in a person’s skin depends on heredity as well as on the amount of recent sun exposure. Some people are able to produce large amounts of melanin in response to UV light, whereas others produce very little. People with albinism (see page 1308) are born being able to make little or no melanin at all.

Sunlight and Skin Damage: Exposure to sunlight prematurely ages the skin. Exposure to UV light is responsible for the wrinkles, both fine and coarse; irregular pigmentation; redness; and leathery, rough texture of sun-exposed skin. Although fair-skinned people are most vulnerable, anyone’s skin will change with enough exposure.

The more sun exposure people have, the higher their risk of skin cancers, including squamous cell carcinoma, basal cell carcinoma, and malignant melanoma (see page 1335).

Treatment: The key to minimizing the damaging effects of the sun is avoiding further sun exposure. Damage that is already done is difficult to reverse. Moisturizing creams and makeup help hide wrinkles. Chemical peels, alpha-hydroxy acids, tretinoin creams, and laser skin resurfacing may improve the appearance of thin wrinkles and irregular pigmentation. Deep wrinkles and substantial skin damage, however, require significant treatment to be reversed.

Sunburn

Brief overexposure to ultraviolet light causes sunburn.

Sunburn causes painful reddened skin and sometimes causes blisters, fever, and chills.

People can prevent sunburn by avoiding excessive sun exposure and by using sunscreens.

Cold water compresses, moisturizers, and nonsteroidal anti-inflammatory drugs ease pain until the sunburn heals.

Sunburn results from a brief (acute) overexposure to ultraviolet (UV) light. The amount of sun exposure required to produce a burn varies with each person’s pigmentation and ability to produce more melanin.

Sunburn results in painful reddened skin. Severe sunburn may produce swelling and blisters. Symptoms may begin as soon as 1 hour after exposure and typically reach their peak within 3 days. Some severely sunburned people develop a fever, chills, and weakness and on rare occasions even may go into shock (characterized by very low blood pressure, fainting, and profound weakness). Several days after a sunburn, people with naturally fair skin may have peeling in the burned area, usually accompanied by itching. These peeled areas are even more sensitive to sunburn for several weeks. People who have had severe sunburns when young are at greater risk of skin cancer in later years even if they have not had long-term sun exposure.

Did You Know…

People can get sunburned even on cloudy days because clouds do not filter ultraviolet light.

Even sunscreens that are waterproof or water-resistant need to be reapplied after swimming.

Prevention

Avoidance: The best—and most obvious—way to prevent sun damage is to stay out of strong, direct sunlight. If sun exposure is unavoidable, the person should seek shade as soon as possible, cover up in UV-protective clothing, and wear sunscreen, a hat, and UV-protective sunglasses. Many materials are capable of filtering or blocking UV radiation, but many are not. Clothing, ordinary window glass, smoke, and smog filter out most of the damaging rays. However, water is not a good filter. UVA and UVB light can penetrate a foot (about 30 centimeters) of clear water. Clouds and fog are also not good filters of UV light—a person can get sunburned on a cloudy or foggy day. Snow, water, and sand reflect sunlight, magnifying the amount of UV light that reaches the skin. People also burn more quickly at high altitudes, where the thin air allows more burning UV light to reach the skin.

Sunscreens: Before exposure to strong direct sunlight, a person should apply a sunscreen, an ointment or cream containing chemicals that protect the skin by filtering out UV light. Older sunscreens tended to filter only UVB light, but many newer sunscreens are now “full spectrum” and effectively filter UVA light as well.

Sunscreens contain substances, such as para-aminobenzoic acid (PABA) and benzophenone, which absorb UV light. Because PABA does not immediately bind strongly to the skin, sunscreens containing PABA must be applied 30 minutes before going out in the sun or into the water. PABA may irritate the skin or cause an allergic reaction in some people. Many sunscreens contain both PABA and benzophenone or other chemicals. These combination sunscreens provide protection from a broader range of UV light. Many sunscreens claim to be either waterproof or water-resistant, but most of these nonetheless require more frequent application among people who are swimming or sweating.

Other sunscreens, called sunblocks, contain physical barriers such as zinc oxide or titanium dioxide. These thick, white ointments block almost all sunlight from the skin and can be used on small, sensitive areas, such as the nose and lips. Some cosmetics contain zinc oxide or titanium dioxide. Newer-formulated sunblocks have a more pleasing thickness and color, which allow them to be combined with other traditional chemical blockers thereby providing even more sun protection to a given formulation.

In the United States, sunscreens are rated by their sun protection factor (SPF) number—the higher the SPF number, the greater the protection. Sunscreens rated between 2 and 12 provide some protection; those rated between 13 and 29 provide good protection; those rated 30 and above provide maximum protection. The SPF, however, only quantifies the protection against UVB exposure; there is no scale for UVA protection.

Treatment

Cold tap water compresses can soothe raw, hot areas, as can skin moisturizers without anesthetics or perfumes that might irritate or sensitize the skin. Nonsteroidal anti-inflammatory drugs (NSAIDs—see page 644) help relieve pain and inflammation. Ointments or lotions containing local anesthetics (eg, benzocaine) temporarily relieve pain but should be avoided because they occasionally trigger an allergic reaction. Corticosteroid tablets also may help relieve the inflammation but are used only for the most serious burns. Specific antibiotic burn creams are required only for severe blistering. Most sunburn blisters break on their own and do not need to be popped and drained. Sunburned skin rarely becomes infected, but if an infection develops, healing may be delayed. A doctor can determine the severity of an infection and prescribe antibiotics if necessary.

Are Tans Healthy?

In a word—no. Although a suntan is often considered an emblem of good health and of an active, athletic life, tanning for its own sake has no health benefit and is actually a health hazard. Any exposure to ultraviolet A or B (UVA or UVB) light can alter or damage the skin. Long-term exposure to natural sunlight causes skin damage and increases the risk of skin cancer. Exposure to the artificial sunlight used in tanning salons is harmful as well. The UVA lights used in these establishments cause the same long-term effects as exposure to UVB light, such as wrinkling and mottled pigmentation (photoaging) and skin cancer. Quite simply, there is no safe tan.

Self-tanning, or sunless, lotions do not really tan the skin but, rather, stain it. They therefore provide a safe way to achieve a tanned look without risking dangerous exposure to ultraviolet rays. However, because they do not increase melanin production, self-tanning lotions do not offer protection from the sun. Therefore, sunscreens should still be used during exposure to sunlight. Results with the use of self-tanning lotions may vary, depending on a person’s skin type, the formulation used, and the manner in which the lotion is applied.

Sunburned skin begins healing by itself within several days, but complete healing may take weeks. After burned skin peels, the newly exposed layers are thin and initially very sensitive to sunlight and must be protected for several weeks.

Photosensitivity Reactions

Sunlight can trigger immune reactions.

People develop itchy eruptions or areas of redness and inflammation on patches of sun-exposed skin.

These reactions typically resolve without treatment.

Some Substances That Sensitize the Skin to Sunlight

ANTIANXIETY DRUGS

Alprazolam

Chlordiazepoxide

ANTIBIOTICS

Fluoroquinolones

Sulfonamides

Tetracyclines

Trimethoprim

ANTIDEPRESSANTS

Tricyclic antidepressants

ANTIFUNGAL DRUGS (taken by mouth)

Griseofulvin

ANTIHYPERGLYCEMICS

Sulfonylureas

ANTIMALARIAL DRUGS

Chloroquine

Quinine

ANTIPSYCHOTICS

Phenothiazines

DIURETICS

Furosemide

Thiazides

CHEMOTHERAPY DRUGS

Dacarbazine

Fluorouracil

Methotrexate

Vinblastine

DRUGS USED TO TREAT ACNE (taken by mouth)

Isotretinoin

HEART DRUGS

Amiodarone

Quinidine

SKIN PREPARATIONS

Antibacterials (chlorhexidine, hexachlorophene)

Antifungal drugs

Coal tar

Fragrances

Sunscreens

Photosensitivity, sometimes referred to as a sun allergy, is an immune system reaction that is triggered by sunlight. Photosensitivity reactions include solar urticaria, chemical photosensitization, and polymorphous light eruption and are usually characterized by an itchy eruption on patches of sun-exposed skin. People may inherit a tendency to these reactions. Certain diseases, such as systemic lupus erythematosus and some porphyrias, also may cause the skin to break out in response to sunlight.

Solar Urticaria: Hives (large, itchy red bumps) that develop after only a few minutes of exposure to sunlight are called solar urticaria. The hives appear within 10 minutes of sun exposure and generally last for only a few hours. A person can be prone to developing solar urticaria for a very long time, sometimes indefinitely. People with large affected areas sometimes have headaches and feel dizzy, weak, and nauseated.

Chemical Photosensitivity: In chemical photosensitivity, people develop redness, inflammation, and sometimes brown or blue discoloration in areas of skin that have been exposed to sunlight for a brief period. This reaction differs from sunburn in that it occurs only after the person has taken certain drugs (such as tetracycline) or chemicals or has applied them to the skin (such as perfume or aftershave). These substances make some people’s skin more sensitive to the effects of ultraviolet (UV) light. Some people develop hives with itching, which indicates a type of drug allergy that is triggered by sunlight.

Polymorphous Light Eruption: This eruption is an unusual reaction to sunlight, the cause of which is not understood. It is one of the most common sun-related skin problems and is most common among women and among people from northern climates who are not regularly exposed to the sun. The eruption appears as multiple red bumps and irregular red patches on sun-exposed skin. These patches, which are itchy, generally appear between 30 minutes and several hours after sun exposure; however, new patches may develop many hours or several days later. The bumps and patches usually go away within several days to a week. Typically, people with this condition who continue to go out in the sun gradually become less sensitive to the effects of sunlight.

Diagnosis

There are no specific tests for photosensitivity reactions. A doctor suspects a photosensitivity reaction when a rash appears only in areas exposed to sunlight. A close review of any diseases, drugs taken by mouth, or substances applied to the skin (such as drugs or cosmetics) may help a doctor pinpoint the cause of the photosensitivity reaction. Doctors may perform tests to rule out diseases, such as systemic lupus erythematosus, that are known to make someone susceptible to such reactions.

Prevention and Treatment

A person with sensitivity to sunlight from any cause should wear protective clothes, avoid sunlight as much as possible, and use sunscreens. If possible, any drugs or chemicals that could cause photosensitivity should be discontinued after consulting with a doctor.

People with polymorphous light eruption or lupus photosensitivity sometimes benefit from treatment with corticosteroids applied to the skin or hydroxychloroquine or corticosteroids taken by mouth. Occasionally, people can be desensitized to the effects of sunlight by gradually increasing their exposure to UV light.