Washing your hands regularly and getting the flu shot every year can help guard against getting a cold or the flu. What else matters?

Is it a cold or the flu?

“The common cold and flu are upper respiratory tract infections caused by many viruses,” says Aric Prather, associate professor of psychiatry at the University of California, San Francisco.

Cold and flu viruses grow in the nose and throat. They’re spread when someone sneezes or coughs on or near you or you touch a contaminated surface and then touch your eyes, nose, or mouth.

It’s your immune system’s response to the virus that makes you miserable.

“We get mucus production, coughs, and sneezing, which are all part of the process of trying to clear the virus from the body as your immune system fights it off,” Prather explains.

How do you know if what you have is a cold or the flu? “If you have a fever and aches, if the symptoms come on rapidly, and if it’s flu season, then the likelihood is high that it’s influenza,” says Bruce Barrett, professor of family medicine and community health at the University of Wisconsin.

But you may not come down with a cold or flu even if you come in contact with the virus. When people are exposed to a cold or flu virus, only some will get infected—that is, the virus will start to multiply in their nose and throat. And only some of them will get symptoms.

“When we put known quantities of a cold virus in people’s noses, 75 percent of them became infected, but only 30 percent actually got sick,” notes Prather. “We’re trying to determine what explains who gets infected and who develops symptoms."

How lifestyle influences risk

Stress. “In a series of experiments, people reported their stress levels first and were then exposed to a bug,” Barrett explains.

“People who rated themselves as more stressed were more likely to have the bug take up shop and replicate and to have worse cold symptoms.” Ditto for those who were unemployed or having marital problems, or who had other stressful experiences.

Exercise. “The data show that people who exercise regularly get fewer respiratory infections,” says Barrett.

In two studies, he randomly assigned roughly 560 people to a control group, to do daily moderate-​intensity exercise, or to reduce stress via meditation for four to eight months. Compared to the control group, the meditators reported 20 percent fewer respiratory infections, and the exercisers’ illnesses were 23 percent shorter (the equivalent of being sick for 1½ fewer days during a weeklong illness). (Granted, the study wasn’t “blinded,” so those groups could have expected to avoid colds or get well faster.)

“I can’t say that we’ve proven beyond a shadow of a doubt that these things work,” says Barrett. “But the body of evidence is such that we’re pretty sure they do. Exactly how much, we don’t know. Who will benefit the most? We don’t know. But there’s no downside to exercising or practicing stress reduction.”

Sleep. In one study, Prather monitored the sleep patterns of 164 people for a week. “Then we shot the cold virus into their nose, quarantined them in a hotel for five days, and tracked who got sick,” he says.

“The odds of getting sick were four times higher in people who slept six hours or less a night than in people who slept seven hours or more. And that was after accounting for factors that are linked with getting a cold, like age, stress, and exercise.”

“These results lend support to the idea that sleep is critical to health,” adds Prather. “People need to make sleep a priority, not just something you do after everything else gets done.”

Photos: PimanKrutmuang/stock.adobe.com, Nestor/stock.adobe.com.

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