More than anything else, your everyday habits can make or break your body’s ability to protect itself from the bug du jour. Andrew Eisenberg, MD, a family physician and medical advisor for the nonprofit group Families Fighting Flu in Sarasota, Florida, says, “I’ve been around people who are very ill, including with the swine flu, and I have not gotten sick. I’m convinced that my behaviors are helping to protect me from infection.”
The things you do—or don’t do—in the course of your daily routine can weaken your immune system, leading to more frequent colds or infections, or just a general sense of blah. The good news is, by dropping the bad habits, you have that many more ways to strengthen your defenses and avoid sickness.
Touching Your Face and Biting Your Nails
Of all the germ carriers that we routinely encounter, two of the worst offenders are literally at arm’s length. “We all have a tendency to put our hands in places they really shouldn’t go,” Dr. Eisenberg says. “We don’t realize the volume of bacteria we pick up, simply because we can’t see them.” And we touch our faces incredibly often: A study from the University of California, Berkeley, found that we make contact with our noses, eyes, or lips an average of once every 4 minutes.
Why it’s bad Carrying around literally handfuls of germs means that habitually touching your face is an easy way to deliver a dose of virus or bacteria right to where it can settle in and make you sick. “The portals of entry are all right there,” Dr. Eisenberg says. “In fact, the main paths of influenza transmission are through the eyes and the nose.”
Make it better Scratching or picking your nose is a habit to drop right away, as is rubbing your eyes or pulling on your eyelids or eyelashes. Nail or cuticle biting is also a problem, not only because you’re introducing germs into your mouth but also because you’re constantly bringing your hands up to your face, potentially spreading bacteria near your eyes and nose in the process.
That’s a Fact 
To maintain personal hygiene, you should respect personal space. Many viruses and bacteria are transmitted via saliva droplets, which can travel a good few feet when propelled by a cough or sneeze. A good rule of thumb is to allow at least 3 feet between yourself and someone else. “With H1N1, the recommendation is to stand back as much as 6 feet,” says recently retired emergency-room physician Kathleen Handal, MD, author of The American Red Cross First Aid & Safety Handbook and president of www.dochandal.com.
To train yourself to keep your hands below chin height, try this mildly painful trick: Wear a rubber band around your wrist and snap it against your inner wrist every time you catch yourself touching your face. It’s a form of negative feedback that will discourage you from picking, poking, and otherwise pawing at your facial parts.
To break a nail-biting habit, the Mayo Clinic recommends regular manicuring, clipping nails short and filing them smooth. You can also try wearing a special bitter-tasting polish to remind you not to put your fingers in your mouth.
If you just can’t seem to keep your hands away from your face, the next best thing is to reduce the microbial load with frequent hand washing. The Centers for Disease Control and Prevention (CDC) recommends lathering up with soap and warm water for at least 20 seconds. Rinse your hands well, then dry with a paper towel or air dryer.
Not Getting Enough Sleep
The occasional bout of sleeplessness probably won’t have any lasting impact on your immune system. But watch out for chronic insomnia or a serious sleep deficit, because these definitely can make you more likely to come down with whatever is going around. When you are trying not to get sick, more rest is best.
Why it’s bad The science is clear: A lack of sleep undermines immune function. According to researchers at Carnegie Mellon University in Pittsburgh, people who got less than 7 hours of sleep were nearly three times more likely to come down with a cold than those who had 8 or more hours of shut-eye.
A study from the CDC found that only 1 in 3 Americans gets close to the 7 to 8 hours we generally need to function at our best. And a very tired 16 percent of adults get less than 6 hours per night, according to the National Sleep Foundation.
All this tossing and turning, and late-to-bed and early-to-rise activity, does not bode well for staying healthy. “Your nervous system is in parasympathetic mode during sleep,” explains Simon Yu, MD, a board-certified internist in St. Louis, Missouri, who also practices complementary and alternative medicine. “If it doesn’t get sufficient downtime to rejuvenate and repair, your immune function will suffer.” The parasympathetic nerves regulate your internal organs, including your heart, and manage crucial functions such as digestion and elimination.
Make it better If you’re finding that time is not on your side when it comes to getting enough sleep, try creating a bedtime ritual, just as you might have done when you were a kid. A good place to start is by lowering the lights and turning off your cell phone when you’re getting ready to turn in. A study from Wayne State University in Detroit found that talking on a cell phone before going to bed caused a 13 percent drop in deep sleep, the kind that helps the body recover from daily wear and tear.
You might also try taking a warm shower about an hour before hitting the hay. The warm water is relaxing, and more important, the drop in body temperature afterward will encourage a natural downshift to sleep.
Many sleep experts recommend keeping your bedroom cool, but not cold—between 54° and 75°F. This, too, turns down your body’s thermostat, which encourages deeper sleep.
Reality Check 
Starve a fever, feed a cold.
There may be something to this popular proverb. Fever—defined as a core body temperature of 100.4°F or higher—is a sign that your body is fending off an invading virus or bacteria. At this critical time in the healing process, you don’t want your body to redirect its resources to digestion, as it would need to do if you’re eating solid foods. Sticking with a liquid diet during a fever is easier on your digestive tract, and it helps maintain your body’s fluid balance.
Smoking
It goes without saying that cigarette smoking is the granddaddy of all bad health habits. Everyone knows that smoking introduces toxins into the body, but you might be surprised to learn exactly how it increases your risk of respiratory infection and flu.
Why it’s bad Cigarettes are the perfect way to become an ideal host for bacteria and viruses, says Ann Carey Tobin, MD, an integrative medicine specialist in private practice in Delmar, New York. Smoking weakens cilia, the tiny projections on lung cells that work to move debris and secretions out and away from the lungs. It also damages the protective bacteria that normally hold the line against unfriendly germs inside the lungs.
When smokers catch a respiratory ailment, they are much more likely to get bacterial infections, Dr. Tobin says. That’s because of their reduced ability to fend off an invading bug.
Make it better There’s really only one way to avoid smoking’s insidious effects, and that’s to quit. You’ve got plenty of help, from medications like Chantix and Zyban to online quit programs and support groups (check out the American Lung Association’s free program at www.ffsonline.org). And don’t forget about nicotine gum and patches.
Fear of—or Overzealous—Flossing
The plaque that forms on teeth and sets the stage for gum disease contains as many as 400 different bacterial species. The best and easiest way to get rid of them is by flossing regularly and properly. That’s something many of us don’t do.
Why it’s bad When we don’t floss, we invite bacterial infection and gum disease, a serious medical condition that can lead to tooth loss, among other problems. Researchers at Columbia University in New York City believe that the chronic inflammation associated with gum disease stresses the immune system, opening the door to other infections.
That’s a Fact
The flu vaccine is about a year and a half behind the times. Scientists gather information about which influenza strains are most likely to hit during a given flu season about 18 months before the season actually starts. Understandably, their projections sometimes miss the mark. There is no way to be certain that the vaccine prepared for any given year will target the right strains. Still, you’re better protected if you get the vaccine than if you don’t.
Just as not flossing can lead to trouble, so can flossing too furiously, Dr. Yu says. Vigorous flossing that injures the gums can spread bacteria into the bloodstream. This condition, called bacteremia, can be responsible for systemic infections that cause fever, aches, and pains.
Make it better Done gently and correctly, flossing shouldn’t hurt. Try to avoid snapping the strand down into your gum; instead imagine that you’re carefully buffing the sides of each tooth with the floss.
If you’re still having trouble, the next time you visit your dentist, ask your hygienist to teach you proper flossing technique. You might also ask which type of floss you should be using. There are lots to choose from, and one may work better for you than others.
For those who are new to flossing or who have limited hand dexterity, the Academy of General Dentistry recommends a prethreaded flosser or floss holder. They look like miniature hacksaws and are available in the dental care aisle of just about any drugstore.
If your gums bleed when you floss, you may already have gum disease. Other signs include red or tender gums and a gum line that seems to pull away from your teeth. See your dentist as soon as possible for treatment that will protect your teeth and your overall health.
Consuming Too Much Caffeine
Caffeine is the active ingredient in two of the most popular drinks in the world: coffee and tea. Although many studies now show that caffeine has measurable health benefits, including antioxidant properties, in this case more of a good thing is not necessarily better.
Why it’s bad Caffeine depletes the body’s stores of zinc, according to Lauri Grossman, DC, a licensed chiropractor and chair of the department of medicine and humanistic studies at the American Medical College of Homeopathy in New York City. “Zinc is a mineral that is necessary for healing,” Dr. Grossman says. “If someone has a cold, it is much more likely to lead to a serious illness such as the flu if the person’s zinc supply is low.”
Make it better You don’t need to give up caffeine entirely. Most studies show negligible negative effects at less than 3 cups of coffee a day; that’s 200 to 300 milligrams of caffeine total. Or you might try switching from coffee to tea, which has about half the caffeine of regular brewed coffee (and many proven health benefits besides).
If you’re committed to giving up caffeine altogether, be sure to taper off over a few weeks to avoid withdrawal headaches and fatigue. You can ease the transition with a “half-caf” blend (such as Green Mountain Roasters or Eight O’Clock brand) or just mix your own.
Not Washing Your Hands
A time-honored protective measure, hand washing is more important than ever when contagious bugs abound. When researchers analyzed the results of studies conducted over a span of 40 years, they found that improvements in hand hygiene have reduced respiratory-illness rates by more than 20 percent.
Still, relatively few of us actually wash our hands as often as we should. If you’ve gotten a little lazy about lathering up, you may want to reconsider.
Why it’s bad When you don’t wash up after touching potentially contaminated surfaces or items, you are unnecessarily exposing yourself to infection, Dr. Tobin says. “Washing your hands is not the only way to keep yourself safe, but it’s definitely a big part of the formula.”
Make it better The CDC still favors plain soap and water as the best for hand washing because it removes the most dirt and debris. But maybe you can’t get to a sink when you really need one. For those occasions, Allison Aiello, PhD, professor of epidemiology at the University of Michigan in Ann Arbor, suggests investing in a bottle of waterless, alcohol-based hand sanitizer. Choose a gel or liquid product that contains at least 60 percent alcohol.
Breathing through Your Mouth
Habitually breathing through your mouth doesn’t just leave you looking perpetually confused. It also increases your risk for respiratory illness.
Why it’s bad About 20 percent of us are chronic mouth breathers, either as an acquired habit or because of asthma or structural problems with the nose, according to physiotherapist Brenda Stimpson, president of Breathingwise in Pasadena, California. Mouth breathers get more colds and flu in part because unlike the lungs, the mouth has no cilia to trap the fine particles that cause irritation. In addition, research shows that cells in the sinuses surrounding the nose produce nitric oxide, which helps to sanitize inhaled air. Air that comes in through your mouth misses out on these barriers, which gives microbes a straight shot to your lungs.
Make it better The best way to break a mouth-breathing habit is to force yourself to breathe through your nose. “It may be difficult at first, because you’ll feel as though you aren’t getting enough air,” Stimpson says. “But over a few hours to a few days of consistent nose breathing, it should become free and clear.”
Shunning the Sun
Most dermatologists will tell you to wear sunscreen every day. And that’s pretty good advice, if your mission is to keep wrinkles at bay. Unfortunately, when you prevent the sun’s UV rays from reaching your skin, you also interfere with your body’s ability to synthesize its own supply of vitamin D.
Why it’s bad As Dr. Tobin observes, vitamin D is very important to the health of your immune system. Studies are finding that vitamin D deficiency contributes to weakened immunity and increased susceptibility to flu, not to mention a greater risk for osteoporosis, depression, and even some cancers.
Make it better Very few foods contain vitamin D naturally; fish and fish liver oils are about the only good sources, and you’d need to consume quite a bit of both to obtain a meaningful amount of the vitamin. The best way to get your D is from the sun.
You needn’t spend a lot of time soaking up the sun’s rays; just 10 to 15 minutes of sun on unprotected skin should cover you. Try to go outside when the sun is least likely to burn—usually before 10 a.m. or after 4 p.m. If you intend to be outdoors for longer than the recommended time frame, then definitely slather on the sunscreen.
If you can’t tolerate the sun, or if you live in a northern climate with limited sunlight, you might consider boosting your vitamin D intake with supplements. Current government guidelines recommend 200 to 600 IU daily, but many researchers believe that we need as much as 1,000 IU a day, if not more. You can always ask your doctor for a blood test to check your vitamin D status if you’re unsure.
Overindulging a Sweet Tooth
It’s perfectly fine to enjoy a thick piece of birthday cake or a box of chocolate-covered raisins at the movie theater … once in a while. But if you eat sweets on a regular basis, you may unwittingly be rolling out the welcome mat for microbes.
Why it’s bad A steady diet of sugary foods can prevent your white blood cells—your body’s natural infection fighters—from effectively engulfing and destroying bacteria. It also causes unhealthy swings in blood glucose and insulin. “Even if you don’t have diabetes, your body will wind up investing a lot of effort in maintaining homeostasis rather than patrolling for illness-causing invaders,” Dr. Eisenberg says.
Make it better If you know you’ll be having a high-sugar day, you can help steady your blood glucose levels by eating more soluble fiber, says Barbara Quinn, RD, author of The Diabetes DTOUR Diet. This form—found in beans, broccoli, and apples, among other foods—of fiber interferes with and slows down carbohydrate absorption in the intestines, which keeps blood sugar on an even keel.
Soda is a major source of sugar in the typical American diet. But you may want to think twice before trading your full-sugar sodas for the zero-calorie variety, which have been linked to metabolic syndrome and a higher risk of heart disease. Instead, try flavored seltzer, which has no calories or artificial sweeteners but provides soda-like fizz and flavor. Or try a sparkling juice, which you can water down with seltzer to reduce your sugar consumption even further.
Being a Worrywart
Trying not to worry is a lot like trying not to move for the next half hour—it’s easier said than done. Goodness knows there’s more than enough to fret about these days. Though you can’t escape stress completely, you should try to keep it from getting the best of you. Otherwise, it can take a toll on your immune system, among many other aspects of your health.
Why it’s bad When you’re under stress, your adrenal glands release cortisol, a potent hormone that is useful in emergency situations but causes trouble over the long run. Chronically high cortisol—common in those who are anxiety prone or type A—challenges the body’s ability to function normally, leading to a depressed immune response and increased vulnerability to infectious illness.
Make it better Stress can result from both positive and negative events in your life, says clinical psychologist Patricia Farrell, PhD. To get a sense of your current stress level, Dr. Farrell suggests doing an online search for the Holmes-Rahe scale and then taking the simple test. Your score may surprise you, but it also should motivate you to take control of the stressors in your life.
One of the easiest ways to improve your ability to handle stress is to exercise regularly. “We’re not talking about pumping iron or even going to a gym,” Dr. Farrell explains. “I tell my patients to walk in place if that is the only activity they can do. Just move your body.”
Dr. Farrell also recommends regular bouts of laughter to protect your immune system against stress’s effects. In several studies, people’s cortisol levels dropped substantially in response to laughter.
Polluting Your Indoor Air
According to the Environmental Protection Agency, we Americans spend up to 90 percent of our time indoors. So maybe it shouldn’t come as a surprise that the concentration of airborne pollutants is worse in our homes, schools, and workplaces than it is outside.
Why it’s bad Indoor air can harbor pollen, mold, dust, pet dander, cigarette smoke, soot, and other substances that irritate your airways and lungs. “When your nose and eyes are moist and itchy, you become an ideal host for infection and an attractive site for bacteria to grow,” Dr. Tobin explains.
Make it better Dr. Yu recommends installing an air filter in your home to remove air pollutants. Be sure to choose a unit with a true HEPA filter to safely remove 99 percent of airborne particles.
Also, be mindful of your indoor air space when cleaning or painting. Choose low-or zero-VOC paints, which have less vaporous chemicals in them. And opt for homemade cleaning products like a simple spray bottle of vinegar and water, which is good for wiping down just about any surface and smells fresh without artificial fragrance.
Attempting to eliminate or cover up bad air smells with scented fresheners only adds another layer of pollutants. “You’re just masking a foul odor by introducing a stronger one,” says James Sublett, MD, chief of pediatric allergy and immunology at the University of Louisville School of Medicine. To really clear the air, leave the scented sprays and other artificial air fresheners on the supermarket shelf and open a window instead.
Ignoring Your Need for Water
Water is the single most important nutrient for your body, and the most plentiful, accounting for 60 percent of your total weight. Allowing yourself to get even a little bit dehydrated can undermine all of your body’s systems, including your immune system.
Why it’s bad As Dr. Grossman explains, not drinking enough water prevents your cells, tissues, and organs from operating at their best. It also impedes your body’s ability to eliminate waste products generated by normal metabolism, stress, and illness. “All of the hand washing in the world won’t get rid of the toxins that are on the inside,” Dr. Grossman says.
Make it better If you just can’t swallow plain old water, by all means try one of the new flavored varieties—but choose wisely. As a rule of thumb, you should steer clear of any water beverage that has along ingredient list. Only buy brands with ingredients that you recognize.
You might try jazzing up a glass of tap or filtered water with an old-fashioned lemon slice, a fresh mint leaf, or some grated ginger. It’s cheaper than a bottled beverage, and it’s available wherever faucets are flowing.
The Pros Know
Sue DeCotiis, MD
Board-certified internal medicine specialist
in private practice in New York City
As an internist, Dr. DeCotiis knows how quickly and easily infections start and how frequently she’s exposed to them as part of her job. Here’s how she avoids becoming a patient herself.
First, I do all the obvious things—washing my hands often and wiping down surfaces like doorknobs, countertops, elevator buttons, and faucets. When I’m out and about, I carry paper towels and use them to grasp door handles and faucet handles, thus limiting my exposure to germs.
In my office, the examination tables are set so that patients are at a right angle to me. That way, when patients cough or sneeze, I don’t get a face full of germs.
At home, I don’t allow handbags or briefcases on tables, kitchen counters, or beds. These things have been on the floor of a bathroom stall or maybe even on the street, picking up all sorts of bacteria and viruses.
Especially during cold and flu season, I make sure to sleep at least 8 hours a night. If I feel tired, I realize that my body is trying to tell me something, and I hit the sack.
Beyond that, I eat lots of garlic in raw or pill form (cooked garlic is probably ineffective). There is no conclusive evidence that it eradicates colds or flu, but some research has shown that it may shorten the duration of a respiratory infection. (People on blood thinners should use garlic sparingly, however.)