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Additional Information From NIAID

Common Cold

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The viruses

One reason why there is no cure for the common cold is that more than 200 different viruses can cause cold symptoms. Some, such as rhinoviruses, seldom produce serious illnesses. Others, such as respiratory syncytial virus (RSV), produce mild infections in adults but can lead to severe lower respiratory tract infections in young children. (The lower respiratory tract includes the lungs.)

Rhinoviruses (from the Greek rhin, meaning “nose”) cause an estimated 30 to 50 percent of all colds. Scientists have identified more than 100 distinct rhinovirus types. For example, rhinovirus C was discovered only in 2007 and is found worldwide. Rhinoviruses grow best at temperatures of about 91ºF, the temperature inside the human nose.

Scientists think coronaviruses cause about 10 to 15 percent of all adult colds. They bring on colds primarily in the winter and early spring. Although many coronaviruses infect animals, only five infect humans, causing respiratory tract illness. How important coronaviruses are as a cause of colds is hard to assess because, unlike rhinoviruses, they are difficult to grow in a laboratory.

Adult cold symptoms also are caused by viruses that are responsible for other, more severe illnesses. These viruses are: adenoviruses, coxsackieviruses, echoviruses, orthomyxoviruses (including influenza A and B viruses, which cause flu), paramyxoviruses (including several parainfluenza viruses), RSV, and enteroviruses.

Researchers still haven't identified the causes of 20 to 30 percent of adult colds, presumed to be viral. Because current advances in technology are leading to new tools to diagnose diseases, however, the next decade undoubtedly will bring significantly greater understanding of the causes of the common cold.

The cold season

In the United States, most colds occur during the fall and winter. This may relate to the opening of schools and the start of cold weather, which prompt people to spend more time indoors and increase the chances that viruses will spread from person to person.

Seasonal changes in relative humidity also may affect the occurrence of colds. The most common cold-causing viruses survive better when humidity is low—the colder months of the year. Cold weather also may make the inside lining of your nose drier and more vulnerable to viral infection.

Other factors

Although a connection exists between the number of cases of the common cold and the fall and winter seasons, there is no experimental evidence that exposure to cold temperatures increases the chances that you will get a cold. There is also no evidence that your chances of getting a cold are related to enlarged tonsils or adenoids.

On the other hand, several research studies show that people who exercise regularly have a significantly reduced number of respiratory tract infections, such as the common cold, compared with those who don't exercise. Research also suggests that allergic diseases that affect the nose or throat and psychological stress may increase your chances of getting infected by cold viruses.

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Last Updated May 20, 2011