If you haven’t gotten sick this season, consider yourself lucky. Millions of people across the country have already come down with COVID-19, influenza, or RSV—and it’s only early December.

There are lots of reasons why winter becomes a contagion fest (more time spent indoors and abundant holiday gatherings, to name a couple). Now, new research published in The Journal of Allergy and Clinical Immunology points to another: the body’s immune defenses don’t work as well when it’s cold outside.

Your nose is built to keep out invaders like viruses and bacteria. If a pathogen tries to enter, it releases a swarm of tiny, fluid-filled sacs meant to attack the intruder. But, as the authors of the new study found, that response is blunted in cold weather, meaning viruses are more likely to bypass the nose’s defenses, get inside your body, and make you sick.

With viruses spreading like wildfire and temperatures dropping, you may want to double down on masking this winter. Your immune system could use the help.

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