Why Is There a Flu Season?

The flu is a respiratory illness caused by contraction of one of the influenza viruses, according to the Centers for Disease Control and Prevention. Influenza viruses, however, do not cause flu season---they simply take advantage of winter.

Temperature

• According to The New York Times, Dr. Peter Palese of Mount Sinai School of Medicine has found that flu season is primarily attributable to cold winter weather, as flu viruses travel much more easily through the air in cold temperatures than warm ones.

Spread

• Unlike the common cold, the flu virus is spread through the air. The common cold is spread mostly by contact.

Location

• Flu season occurs at different times of the year in different places but always at the coldest time. Flu season in the Northern Hemisphere lasts from November to March but occurs from May to September in the Southern Hemisphere. Some tropical climates, in fact, experience no flu season at all.

Schools

• Certain populations, such as children, the elderly and pregnant women, are more likely to contract the flu virus, according to the CDC. The New York Times reports that researchers say most large-scale flu epidemics can be traced back to an initial outbreak in school children.

Theories/Speculation

• Researchers have speculated in the past that the flu season was caused by people staying indoors more often in winter and being packed together in public transportation. But these explanations alone do not explain why flu season occurs in the winter, Palese says.