Why people get more colds and flu during winters

In what scientists are calling a breakthrough, they have finally figured out the biological reasoning behind an uptick in cold and cases of flu in winter. A study published, on Tuesday, found that cold air leads to a weakened immune response from the body, particularly the nose. 

“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,” Stanford University School of Medicine professor, Dr Zara Patel, who was not a part of the study told CNN. 

Published in The Journal of Allergy and Clinical Immunology, the study found that since the nose is the first site of contact for respiratory viruses as well important for the body’s immune response. 

This factor makes the nose particularly vulnerable to lower temperatures, in fact, the study found that lowering the temperature by just five degrees Celsius reduced the billions of virus and bacteria-fighting cells in the nostrils, by at least 50 per cent. 

“Cold air is associated with increased viral infection because you’ve essentially lost half of your immunity just by that small drop in temperature,” said the co-author of the study, Dr Benjamin Bleier, a rhinologist and the director of otolaryngology at Massachusetts Eye and Ear. 

According to Bleier, that’s why masks work because not only do they protect you from “direct inhalation of viruses”, they also act like a “sweater on your nose” protecting it from the chilly air. Bleier and her team conducted a study on four participants who were exposed to a 4.4-degree-Celsius temperature for 15 minutes. 

However, the study was completed in vitro which means it was not conducted on a live subject but on human tissue in a lab. Notably, they also found that the nose increases the replication of decoy extracellular vesicles by 160 per cent when faced with lower temperatures.  

“EVs act as decoys, so now when you inhale a virus, the virus sticks to these decoys instead of sticking to the cells,” said Bleier to CNN. The co-author also said that these EVs do not divide like normal cells; they are mini versions of them, “specifically designed to go and kill these viruses.” Since they have up to 20 times more receptors than the original cells which enhances their capability to trap germs. 

Subsequently, these EVs are expelled with the mucus out of the body as it continues to fight the germs and further multiply. However, the study also noted a 42 per cent drop in the number of EVs when exposed to just a few more degrees drop in temperature. Additionally, those that do remain have at least 70 per cent fewer receptors on each vesicle making it less sticky and lessening your ability to fight off respiratory infections by half, as mentioned earlier.