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In the United States, cold and flu season begins around late August and lasts until March or April. One possible cause of this season is the opening of schools in the fall, which brings more people in closer proximity to one another. Changes in relative humidity may also play a role.
In the United States, most colds and flus occur during the seasons of fall and winter. Beginning in late August or early September, the rate of colds and flus increases slowly for a few weeks and remains high until March or April, when it declines.
One possible cause of cold and flu season may relate to the opening of schools and to the arrival of colder weather, which prompt people to spend more time indoors and increase the chances that viruses will spread to you from someone else.
Seasonal changes in relative humidity also may affect how often people get colds and flus. The most common cold and flu viruses survive better when humidity is low -- during the colder months of the year. Cold weather also may make the inside lining of your nose drier and more vulnerable to viral infection.