Why Does the Flu Come Back Every Year?

Why Does the Flu Come Back Every Year?


Have you ever thought about how strange it is that there is a flu season? After all, the flu is a virus that lives in a human host at a stable 98 degrees. Your body’s internal temperature doesn’t really change with the season, so why does the flu seem to wax and wane with the cold weather?

Let’s take a closer look at why the flu has a season, and what you can do to prevent its spread.

What Is the Flu?

The flu, also known as “influenza,” is a respiratory illness caused by a viral infection. It’s extremely easy to spread the flu to others, and the illness it causes is unpleasant, but not usually life-threatening. Typically, those who die from the flu are elderly, very young, or immunocompromised.

Flu Season

Flu season in the northern hemisphere usually starts in October before intensifying into December, when the number of cases reaches a peak. The opposite is true in the Southern hemisphere: the flu starts there in June and runs through September. As you might imagine, this means that the virus seems to flourish in cold weather.

In fact, the English-language name for the illness, “influenza,” could be referencing the Italian term for the illness, which translates to “influence of the cold”. In reality, cold doesn’t need to be present for the flu to occur: the flu virus is what causes the illness. So, why does the illness seem to be so much more successful at spreading during the winter months?

Lifestyle Changes

People behave differently in the winter than they do in the summer. People crowd into enclosed spaces, keep windows closed, and have little exposure to sunlight in the winter months. This could all lead to people having more chances to be exposed to someone with the flu virus during these colder months. Moreover, the lack of exposure to sunlight means that many people have less vitamin D in their system during winter, which could lead to a weakened immune response.

The Virus

Research also suggests that the virus responsible for the flu may survive for longer outside of a host when conditions are cold, dry, and dark. The bright, hot, humid conditions of summer appear to be far from ideal for the spread of the virus.

All of this is to say, flu season isn’t just something made up to sell you on getting flu medicine. Make sure you get your flu shot every year and take all precautions to prevent the spread of illness, like washing your hands and avoiding touching your face.