More than 200 different viruses are known to cause the symptoms of the common cold. Some, such as the rhinoviruses, seldom produce serious illnesses. Others, such as parainfluenza and respiratory syncytial virus, produce mild infections in adults but can lead to severe lower respiratory tract infections in young children.
Rhinoviruses (from the Greek rhin, meaning “nose”) cause an estimated 30 to 35 percent of all adult colds, and are most active in early fall, spring, and summer. Scientists have identified than 110 distinct rhinovirus types. These agents grow best at temperatures of about 91 degrees Fahrenheit, the temperature inside the human nose.
Scientists think coronaviruses cause a large percentage of all adult colds. They bring on colds primarily in the winter and early spring. Of the more than 30 kinds, three or four infect humans.
The importance of coronaviruses as a cause of colds is hard to assess because, unlike rhinoviruses, they are difficult to grow in the laboratory.
Approximately 10 to 15 percent of adult colds are caused by viruses also responsible for other, more severe illnesses: adenoviruses, coxsackieviruses, echoviruses, orthomyxoviruses (including influenza A and B viruses, which cause flu), paramyxoviruses (including several parainfluenza viruses), respiratory syncytial virus, and enteroviruses.
The causes of 30 to 50 percent of adult colds, presumed to be viral, remain unidentified. The same viruses that produce colds in adults appear to cause colds in children. The relative importance of various viruses in pediatric colds, however, is unclear because it’s difficult to isolate the precise cause of symptoms in research studies of children with colds.
There is no evidence that you can get a cold from exposure to cold weather or from getting chilled or overheated.
There is also no evidence that your chances of getting a cold are related to factors such as exercise, diet, or enlarged tonsils or adenoids. On the other hand, research suggests that psychological stress and allergic diseases affecting your nose or throat may have an impact on your chances of getting infected by cold viruses.