What Is a Cold?

A cold is an infectious disease characterized by a common set of symptoms—including a stuffy or runny nose, sore throat, sneezing, mild to moderate cough and perhaps mild fever. Colds are believed to be caused by any of more than 200 viruses.

The rhinovirus—one of the most common cold culprits—comes in more than 100 varieties and usually strikes in the spring, summer and early fall. The rhinovirus causes an estimated 30 to 35 percent of all adult colds. Coronaviruses, which cause about 10 to 20 percent of adult colds, tend to hit in the winter and early spring.

A small percentage of colds are caused by viruses that also are responsible for other, more severe illnesses such as certain strains of influenza. Almost half of adult colds are caused by still other viruses that have yet to be identified!

Cold symptoms are typically the reaction of your body's immune system fighting the invading virus. The infected cells trigger production of body chemicals that lead to swelling and inflammation of the nasal membranes and passages, overflow levels of certain other fluids—causing the "runny" nose—and increased production of protective mucus.

In the U.S., children can average six colds a year; some children get double that. Adults usually get fewer colds— two to four a year, and people over age 60 get fewer still—on average, less than one per year.