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 33 degrees Celsius [about 91 degrees Fahrenheit (F)], the temperature of the human nasal mucosa.
Coronaviruses are believed to cause a large percentage of all adult colds. They induce colds primarily in the winter and early spring. Of the more than 30 isolated strains, three or four infect humans. The importance of coronaviruses as causative agents is hard to assess because, unlike rhinoviruses, they are difficult to grow in the laboratory.

Responsible for other, more severe illnesses Approximately 10 to 15 percent of adult colds are caused by viruses also: adenoviruses, coxsackieviruses, echoviruses, orthomyxoviruses (including influenza A and B viruses), paramyxoviruses (including several parainfluenza viruses), respiratory syncytial virus and enteroviruses.

Remain unidentified the causes of 30 to 50 percent of adult colds, presumed to be viral,. In adults appear to cause colds in children the same viruses that produce colds. The relative importance of various viruses in pediatric colds, however, is unclear because of the difficulty in isolating the precise cause of symptoms in studies of children with coldsallergic disorder .