The common cold, also called viral rhinitis, is one of the most common infectious diseases in humans. The infection is usually mild and improves without treatment. Because of the large number of people who get the common cold, this illness results in nearly 26 million days of missed school and 23 million days of absence from work every year in the United States. The average American has 1 to 3 colds per year.
The common cold is an upper respiratory infection that is caused by several families of viruses. Within these virus families, more than 200 specific viruses that can cause the common cold have been identified. The virus family that causes the most colds is called rhinovirus. Rhinoviruses cause up to 40% of colds, and this virus family has at least 100 distinct virus types in its group. Other important upper respiratory virus families are named coronavirus, adenovirus and respiratory syncytial virus. Since so many viruses can cause cold symptoms, development of a vaccine for the common cold has not been possible.
Rhinoviruses cause most colds in the early fall and spring. Other viruses tend to cause winter colds and their symptoms can be more debilitating. There is no evidence that going out in cold or rainy weather makes you more likely to catch a cold.