Well over 200 virus strains are implicated in causing the common cold, with rhinoviruses being the most common. They spread through the air during close contact with infected people or indirectly through contact with objects in the environment, followed by transfer to the mouth or nose. Risk factors include going to daycare, not sleeping well, and psychological stress. The symptoms are mostly due to the body's immune response to the infection rather than to tissue destruction by the viruses themselves. In contrast, those affected by influenza can show similar symptoms as people with a cold, but symptoms are usually more severe. Additionally, influenza is less likely to result in a runny nose.
The common cold is the most frequent infectious disease in humans. The average adult gets two to three colds a year, while the average child may get six to eight. Infections occur more commonly during the winter. These infections have existed throughout human history.
The color of the sputum or nasal secretion may vary from clear to yellow to green and does not indicate the class of agent causing the infection.
A cold usually begins with fatigue, a feeling of being chilled, sneezing, and a headache, followed in a couple of days by a runny nose and cough. Symptoms may begin within sixteen hours of exposure and typically peak two to four days after onset. They usually resolve in seven to ten days, but some can last for up to three weeks. The average duration of cough is eighteen days and in some cases people develop a post-viral cough which can linger after the infection is gone. In children, the cough lasts for more than ten days in 35–40% of cases and continues for more than 25 days in 10%.