What Is a Cold?
The common cold is a contagious viral infection of the upper respiratory tract.
Most adults catch a cold from time to time, but kids can get 8 colds per year or more. They're the top reason kids visit the doctor and miss school.
What Causes a Cold?
Most colds are caused by viruses — known as — carried in invisible droplets in the air or on things we touch. These viruses can get into the protective lining of the nose and throat, setting off an immune system reaction that can cause a sore throat, headache, and trouble breathing through the nose.
Dry air — indoors or outside — can lower resistance to infection by the viruses that cause colds. So can being a smoker or being around someone who smokes. Smokers are more likely to catch a cold than people who don't smoke, and their symptoms probably will be worse and last longer, and can even lead to bronchitis or pneumonia.
Not wearing a jacket or sweater when it's chilly, sitting or sleeping in a draft, and going outside while your hair's wet do not cause colds.
What Are the Signs & Symptoms of a Cold?
The first symptoms of a cold are often a tickle in the throat, a runny or stuffy nose, and sneezing. Kids with colds also might feel very tired and have a sore throat, cough, headache, mild fever, muscle aches, and loss of appetite. Mucus from the nose may become thick yellow or green.
Are Colds Contagious?
Colds are the most common infectious disease in the United States. They're very contagious, especially in the first 2–4 days after symptoms start. They can even spread for a couple of weeks after someone starts feeling sick.