Common Cold - Causes

Colds are caused by more than two hundred different viruses. The most common groups of viruses are rhinoviruses and coronaviruses. Knowing which virus has caused a cold is not important because treatment does not depend on the type of virus.

People with colds are contagious (can pass on the virus) during the first two to four days of infection. The virus can be passed in various ways. When an infected person coughs, sneezes, or speaks, for example, fluid droplets containing the virus are discharged. People nearby may breathe in the droplets and may then become infected.

Cold viruses can be passed from person to person through direct contact, such as shaking hands. The viruses can also be spread through nonliving objects, such as doorknobs, telephones, and toys. This method of transmission is common in day-care centers. A child with a cold may transfer the cold virus to a toy with which he or she is playing. When another child picks up the same toy, he or she may also pick up the cold virus.