context: var s_context; s_context= s_context || {}; s_context['wb.modimp'] = 'vidfloat'; if(webmd.useragent && webmd.useragent.ua.type === 'desktop'){ webmd.ads2.disable Initial Load(); webmd.ads2.disable Ads Init = true; $(function() { webmd.p.pim.increment(); $('.responsive-video-container').insert After('.module-social-share-container'); require(['video2/1/responsive-player/video-loader'], function(video Loader) { video Loader.init({ autoplay: webmd.useragent.ua.type === 'desktop' && ! !s_sensitive, chron ID: $('article embeded_module[type=video][align=top]:eq(0)').attr('chronic_id'), continuous Play: true, cp Options: { flyout: true }, display Ads: true, mode: 'in-article', sticky: true }) }); }); } else { $(function(){ $('.responsive-video-container').remove(); }); } A runny nose, scratchy throat, and nonstop sneezing -- you can't miss the signs of a cold. But mystery shrouds a lot of other things about it. Why do you seem to get them so often while your best friend stays well? And more importantly, how can you stay healthy this year? Get the lowdown on the all-too-common common cold. It's an illness caused by a tiny, infectious thing called a virus. More than 200 types lead to your misery, but the most common one is the rhinovirus, which is thought to be responsible for at least 50% of colds. Other viruses that can cause colds include coronavirus, respiratory syncytial virus, influenza and parainfluenza. Colds cause a lot of people to stay home. The CDC says 22 million school days are lost each year in the U. S. because of them. Some estimates say that Americans have 1 billion colds a year. For more detail, see Common Cold Causes. You can catch it from another person who is infected with the virus. This can happen by direct physical contact with someone who has a cold, or by touching a surface contaminated with their germs -- like a computer keyboard, doorknob or spoon --- and then touching your nose or mouth. You can also catch it from infected droplets in the air released by a sneeze or a cough. A cold begins when a virus attaches to the lining of your nose or throat. Your immune system -- the body's defense against germs -- sends out white blood cells to attack this invader. Unless you've had a run-in with that exact strain of the virus before, the initial attack can fail and your body sends in reinforcements. Your nose and throat get inflamed and make a lot of mucus. With so much of your energy directed at fighting the cold virus, you're left feeling tired and miserable. One myth that needs to get busted: Getting chilly or wet doesn't cause you to get sick. But there are things that make you prone to come down with a cold. For example, you're more likely to catch one if you're extremely tired, under emotional distress, or have allergies with nose and throat symptoms. When a cold strikes, you may have symptoms like: Scratchy or sore throat Sneezing Stuffy nose Watery eyes Mucus draining from your nose into your throat More severe symptoms, such as high fever or muscle aches, may be a sign that you have the flu rather than a cold. For more detail, see Common Cold Symptoms: What You Might Feel. Children have about 5-7 colds per year. A big part of the reason: They spend time at school or in day care centers where they're in close contact with other kids most of the day. Also, kids aren't as conscientious about sneezing into the crook of their arm or frequent hand washing â not to mention keeping their hands to themselves. They may not have built up immunity to as many varieties (or strains) of colds as an adult. For in-depth information, see Children and Colds. In the U. S., most colds happen during the fall and winter. Beginning in late August or early September, the rate increases slowly for a few weeks and remains high until March or April, when it goes down. The reason may partly have to do with the opening of schools. Cold weather may also play a role because it leads you to spend more time indoors, where you're in closer contact with people who are contagious. Changes in humidity in different seasons may also affect how often people get sick. The most common cold viruses survive better outside the body. Also, cold weather may make the lining of your nose drier and more vulnerable to an infection by a virus. Most colds last about 7 to 10 days, but if your symptoms linger, you may need to call the doctor. Sometimes, colds lead to an infection by bacteria in in your lungs, sinuses, or ears. If that happens, your doctor may prescribe antibiotics, which work against bacteria but not against viruses. For more detail, see Common Cold Complications. Need more info about the common cold? See 10 Questions About Colds.