Cold--Causes

Common Cold--Causes

The viruses

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 precipitate severe lower respiratory 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. More than 110 distinct rhinovirus
types have been identified. 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 studies of children with colds.

The weather

There is no evidence that you can get a cold from exposure to cold weather or
from getting chilled or overheated.

Other factors

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.