TRENDING SCIENCE: Why do we get sick more easily in winter?

The temperature starts to drop, there’s a chill in the air. You know what that means. It’s cold and flu season. We seek for the indoors, and that’s where viruses can spread more easily.

This much we know. What we didn’t have until now was a biological explanation as to why respiratory virus infections increase in colder seasons.According to new research in ‘The Journal of Allergy and Clinical Immunology’, the answer has been right under our … noses. The nose has defences to stop invaders, such as viruses and bacteria. As the temperature dips, this natural immune response is weakened.

The research team found that the cold air itself damages our immune response that occurs in the nose. This causes more respiratory illnesses.

“Cold air is associated with increased viral infection because you’ve essentially lost half of your immunity just by that small drop in temperature,” co-author and rhinologist Dr Benjamin Bleier, director of otolaryngology at Massachusetts Eye and Ear hospital and associate professor at Harvard Medical School in Boston, told the ‘New York Post’.

“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,” rhinologist Dr Zara Patel, professor of otolaryngology and head and neck surgery at Stanford University School of Medicine in California, explained to ‘CNN’.Cells in the nose release extracellular vesicles (EVs) into the nasal mucus that attack bacteria once it’s detected. EVs carry receptors that fasten to and block the virus. Findings revealed that the nose boosts EV production by 160 % during an invasion. These vesicles “can’t divide like cells can, but they are like little mini versions of cells specifically designed to go and kill these viruses,” Dr Bleier further elaborated. “EVs act as decoys, so now when you inhale a virus, the virus sticks to these decoys instead of sticking to the cells.”

The researchers exposed healthy volunteers to cold conditions – 40 °F (4.4 °C) – for 15 minutes. EVs that attacked bacteria entering the nose shrunk by about 42 %.

Next, the research team will investigate how the nose’s immune response protects against all types of invaders and how to keep immunity high.

Oh, and remember those masks? “Not only do masks protect you from the direct inhalation of viruses, but it’s also like wearing a sweater on your nose,” commented Dr Bleier. Dr Patel is all for it, too: “The warmer you can keep the intranasal environment, the better this innate immune defense mechanism will be able to work. Maybe yet another reason to wear masks!”