At some point during the winter months, you’ve likely been warned: Don’t go outside without a coat, you’ll catch a cold. While that’s not exactly true, it’s in the ballpark.

Cold weather does make it easier to get a cold or the flu. Studies have shown that cold weather makes the outer membrane of the rhinovirus that causes the common cold and influenza more solid and rubbery. The virus also remains infectious longer and replicates faster in colder temperatures. That’s why it spreads more easily in winter.

In case you’re wondering, scientists don’t yet know if weather affects the COVID-19 virus.

Winter’s dry air also plays a role. Studies have found that humidity levels tend to fall in the weeks before a significant flu outbreak. This may help explain why the flu doesn’t spread during the summer.

Inhaling cold, dry air adversely affects your respiratory tract, drying out mucous membranes in your nose and throat and weakening your immune system, making it easier for viruses to take hold. Wearing a scarf over your nose and mouth can help.

Then there’s the smaller number of daylight hours during the winter. The sun is a major source of vitamin D, which is essential to the health of the immune system. And with more people staying indoors together, it’s easier for viruses to spread.

Some of the ways you can defend yourself from catching a cold will sound familiar as we approach one year of battling the coronavirus: Wash your hands often, avoid touching your face, clean surfaces in your home.

Also, stay hydrated. It’s essential to drink more water during dry months. Eat a healthy diet and stay physically active. And, of course, get a flu shot.