It's the peak of cold and flu season, which generally starts in the fall and lasts through spring.

According to the CDC, peak flu season usually falls between December and February, which also happen to be some of the coldest months of the year in the United States.

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For years, it was thought the reason for the uptick in viruses over winter was because people spent more time indoors but a breakthrough study finally revealed the true reason.

The breakthrough study, titled "Cold exposure impairs extracellular vesicle swarm–mediated nasal antiviral immunity," was published early December in the Journal of Allergy and Clinical Immunology.

The research found that cold air weakens the body's immune response, particularly in the nose. Since the nose is one of the first sites of contact for respiratory viruses, its weakened immune response plays a huge role in getting sick.

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In fact, the study found that reducing the internal temperature of the nose by just 9 degrees Fahrenheit killed nearly 50% of the cells that work to fight off viruses and bacteria.

In a Harvard Medical School press release, senior author of the study, Benjamin Bleier, explained: "Conventionally, it was thought that cold and flu season occurred in cooler months because people are stuck indoors more where airborne viruses could spread more easily. Our study, however, points to a biological root cause for the seasonal variation in upper respiratory viral infections we see each year, most recently demonstrated throughout the COVID-19 pandemic."

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For the study, researchers exposed four participants to 40-degree Fahrenheit temperatures for 15 minutes before examining the inside of their noses. Their findings account for why the colder months of the year are associated with, and often referred to as, cold and flu season. The brisk, winter air means greater cold exposure for your nose.

In an interview with CNN, Dr. Zara Patel with Stanford University said, "This is the first time that we have a biologic, molecular explanation regarding one factor of our innate immune response that appears to be limited by colder temperatures."

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According to CNN, the researchers found that the nose is armed with extracellular vesicles (EVs) that multiply when a virus is detected. The EVs work to block the virus from entering deeper into the body via the nose, but those mechanisms are depleted when the nose is exposed to cold air.

Keeping your nose warm could prove a lot more advantageous than we once thought. While it may not be possible to walk around with a nose-warmer on all day, keeping a scarf wrapped around your face in cold air or wearing a face mask could help protect your body from the effects of the cold.