The common cold virus is usually spread in one of two main ways. By breathing or swallowing droplets in the air containing the virus; or by contacting infected nasal mucus or contaminated objects. The most common method of transmitting the cold virus has not been determined. The viruses may survive for a long time in the environment. Viruses may then be transmitted from the hands to the eyes or nose where infection occurs. People sitting close together appear at greater risk of becoming infected. Transmission is common in day cares and at schools, due to the closeness of many children with little immunity and frequently poor hygiene. These infections are then brought home to other members of the family. There is no evidence that the air on commercial flights transmits cold viruses. Rhinoviruses are most infectious in the first three days of cold symptoms. They are much less infectious afterwards.