Why is there a flu season?

It’s not the flu virus goes into a dormant state based on the seasons. It’s always active. So why is there supposedly a flu season? Or is that just a myth and the number of flu cases is actually more or less constant year round?

In cold weather people stay indoors more which makes it easier to spread the flu around. At least that is what I always have heard.

Yes, in colder weather people tend to spend more time indoors, among other people who may be contagious . . . especially workers and kids in school. In summer, at least most kids aren’t in school.

Does the large amount of holiday travel have anything to do with it as well? Lots of people crammed on planes spreading germs as well as bringing them from one part of the country to another.

Is that even true in the modern world? Most adults spend the entire day indoors at work regardless of the season. Most adults then spend their evenings indoors at home with the families (or watching TV) too.

And in the modern world of two-working family homes, don’t most kids spend their summers in day care and camp and things like that?

Cold air causes sinuses to dry up thus the ability to resist germs goes down. People are indoors more.

Sure it is. The time spent indoors and my proximity to others does up in the winter quite a bit. Even a small percentage of extra time doing these things raises risk.

Also, the outer shell of a viruses changes in warmer weather and makes it less efficient:

At winter temperatures, the virus’s outer covering, or envelope, hardens to a rubbery gel that could shield the virus as it passes from person to person, the researchers have found. At warmer temperatures, however, the protective gel melts to a liquid phase. But this liquid phase apparently isn’t tough enough to protect the virus against the elements, and so the virus loses its ability to spread from person to person.

So, if winter contributes to it by peoples’ staying indoors more, and thus are in closer proximity to share pathogens, wouldn’t there also be a spike in other communicable diseases other than flu?

Some recent research suggests that high absolute humidities kill the flu virus faster and make it less transmissible. Absolute humidities are higher in warm weather.

Here’s a discussion:

You can find others using “absolute humidity” and “flu virus” as search terms.

There’s a theory that susceptibility to colds/flu rises in cold weather because people get less sunlight and hence have lowered levels of vitamin D. Adequate (over 30) or good (over 50) vitamin D blood serum levels are being proven to be essential for many aspects of general health. The majority of people in our country and other 1st world countries are D-deficient.