Causes of Common Cold
There are over 200 viruses known to cause the common cold. Rhinoviruses cause colds in an estimated 30 to 35 percent of all adults. Other viruses, such as adenovirus and orthomyxovirus, can cause cold symptoms along with more serious conditions. In 30 to 50 percent of all adults with colds, the cause remains unidentified, although it is presumed to be viral in nature.
What Causes the Common Cold?The common cold is caused by a virus. More than 200 different viruses are known to cause the common cold. Some, such as the rhinovirus, seldom produce serious illnesses. Others, such as parainfluenza and respiratory syncytial virus, produce only mild infections in adults, but can cause severe lower respiratory infections in young children.
Rhinoviruses (from the Greek word rhin, meaning "nose") are the common cold causes in an estimated 30 to 35 percent of all adults, 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.
Coronaviruses also cause a large percentage of all adult colds. They bring on cold symptoms primarily in the winter and early spring. Of the more than 30 types of coronaviruses, only 3 or 4 infect humans. The importance of coronaviruses as common cold causes is hard to assess, because, unlike rhinoviruses, they are difficult to grow in the laboratory.
Approximately 10 to 15 percent of all adult colds are caused by viruses also responsible for other, more severe, illnesses, such as:
- Orthomyxoviruses (including influenza A and B viruses, which cause flu)
- Paramyxoviruses (including several parainfluenza viruses)
- Respiratory syncytial virus