MARK CLARKE / SCIENCE PHOTO LIBRARY MARK CLARKE / SCIENCE PHOTO LIBRARY
Common cold. Ten-year-old girl with a cold sits indoors coughing. Inflammation of the upper respiratory tract due to infection with common cold viruses may cause coughing. The coughing reflex clears the airways of excess mucus and phlegm. The common cold can be caused by almost 200 different viruses. It is most common in school children as they get exposed to many different viruses that they are not yet immune to.
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