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Not getting a severe cold requires two things: avoiding viruses and keeping your immune system strong. Avoidance is straightforward: Give a wide berth to people sneezing, coughing, and blowing their noses. The specific thing you're trying to evade is virus-carrying mucus, which sounds easy enough – but it's not. Mucus from runny noses, hacking coughs, and sneezes can protect viruses for hours as they sit invisibly on surfaces everywhere. Wash your hands frequently. Soap and water are best, but if you're in a bind, hand sanitizer (containing alcohol) will do. And don't worry as much about direct saliva – swapping spit by, say, kissing or sharing a drink probably won't get you sick, says Dr. Gailen D. Marshall Jr., the chair of allergy and immunology at the University of Mississippi Medical Center, because saliva alone doesn't carry pathogens.

Keeping your immune system strong in cold season is tougher. To start, you need to sleep more. People getting less than seven hours in the weeks before they're exposed to a cold are three times more likely to get sick than people sleeping eight hours or more. Exercise is trickier. A number of studies have indicated that frequent exercisers get about a third fewer colds than more sedentary people, but don't push it too hard – research also shows that too much (90 minutes or more) can reverse the benefits. Additionally, the immune system needs a variety of nutrients to function. The best way to get all you need is to follow a Mediterranean-style diet, full of whole fruits and vegetables, beans, nuts, and fish. Studies have pointed to the benefits of some specific foods, too, such as onions and apples, which, according to Jo Robinson, author of 'Eating on the Wild Side,' contain a range of vitamins as well as quercetin, an antioxidant that may help reduce the incidence of colds. Pass over the multivitamins for whole foods, which have a wider array of nutrients and whose benefits are better documented.