Both colds and the flu are contagious and are caused by viruses. However, the viruses that cause colds (for example, rhinoviruses) are not the same as those that cause the flu (influenza viruses)
Although the typical incubation period for influenza is about one to four days, some adults can be contagious from about one day before onset of symptoms for up to two weeks.
. Other people who develop complications, such as pneumonia, may extend the contagious period for a week or two.
For colds, most individuals become contagious about a day before cold symptoms develop and remain contagious for about five to seven days. Some children may pass the flu viruses for longer than seven days