The Cause of Cold And Flu: Winter

Joseph Godwin

Everyone is aware that coolness in the air signals the beginning of cold and flu season, which is when it seems like everyone you know is suddenly sniffling, sneezing, or worse. It almost seems as though those annoying cold and flu viruses arrive with the first winter storm.

However, germs are always present; just think back to the last summertime cold you had. Why then do people tend to get the flu, colds, and now Covid-19 more often when the temperature is cold?

The authors of a recent study believe they may have discovered the biological cause of the seasonal increase in respiratory diseases, which they are hailing as a scientific triumph. It turns out that the immunological reaction taking place in the nose is harmed by the chilly air itself.

“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," Dr. Zara Patel, a rhinologist and professor of otolaryngology and head & neck surgery at Stanford University School of Medicine in California, made this statement. She wasn't a part of the recent study.

According to a study published on Tuesday in The Journal of Allergy and Clinical Immunology, even a little decrease in nasal temperature of 9 degrees Fahrenheit or 5 degrees Celsius can destroy over 50% of the billions of bacteria and virus-fighting cells in the nostrils.

Dr. Benjamin Bleier, an otolaryngologist and associate professor at Harvard Medical School in Boston, a specialist in rhinology, and also the director of otolaryngology at Massachusetts Eye and Ear stated: “Cold air is associated with increased viral infection because you’ve essentially lost half of your immunity just by that small drop in temperature.”

Patel wrote in an email, “It's important to remember that these are in vitro studies, meaning that although it is using human tissue in the lab to study this immune response, it is not a study being carried out inside someone’s actual nose. Often the findings of in vitro studies are confirmed in vivo, but not always.”

Hornet’s Nest

Bleier and his team, together with coauthor Mansoor Amiji, who is the head of the department of pharmaceutical sciences at Northeastern University in Boston, went on a scientific sleuthing mission to discover why this happens.

The nose, the body's primary port of entry, is invaded by a respiratory virus or bacteria. The scientists found that the front of the nose picks up on the germ right away, much before the back of the nose even notices the invader.

Extracellular vesicles, or EVs, are the name for the basic duplicates of cells that the nose's lining cells produce as soon as this happens.

“EVs can’t divide as cells can, but they are like little mini versions of cells specifically designed to go and kill these viruses. EVs act as decoys, so now when you inhale a virus, the virus sticks to these decoys instead of sticking to the cells,” Bleier stated.

The cells then eject those "Mini Me" invaders into nasal mucus (yes, snot), where they prevent the germs from spreading and reaching their intended targets.

“This is one of, if not the only part of the immune system that leaves your body to go fight the bacteria and viruses before they actually get into your body,” Bleier explained.

According to Bleier, after being produced and dispersed into nasal secretions, the billions of EVs begin to swarm the roving germs.

“It’s like if you kick a hornet’s nest, what happens? You might see a few hornets flying around, but when you kick it, all of them fly out of the nest to attack before that animal can get into the nest itself. That’s the way the body mops up these inhaled viruses so they can never get into the cell in the first place,” he muttered.

A Significant Boost In Immunity

The study discovered that the nose produces 160% more extracellular vesicles when it is under attack. The billions of extracellular vesicles in the nose had a greater capacity to inhibit viruses because they had much more receptors on their surfaces than the original cells.

“Just imagine receptors as little arms that are sticking out, trying to grab onto the viral particles as you breathe them in. And we found each vesicle has up to 20 times more receptors on the surface, making them super sticky,” Bleier said.

Additionally, the body's cells carry micro RNA, a viral killer that combats invasive pathogens. However, the study discovered that EVs in the nose had 13 times as many micro RNA sequences as normal cells.

As a result, the nose has some additional superpowers when fighting. But what happens to these benefits when it gets cold?

Bleier and his team measured the conditions inside four study participants' nasal cavities after exposing them to temperatures of 40 degrees Fahrenheit (4.4 degrees Celsius) for 15 minutes.

“What we found is that when you’re exposed to cold air, the temperature in your nose can drop by as much as 9 degrees Fahrenheit. And that’s enough to essentially knock out all three of those immune advantages that the nose has,” Bleier asserted.

You don’t have to wear a nose sock

As it turns out, the pandemic gave us exactly what we need to help fight off chilly air and keep our immunity high, Bleier said.

“Not only do masks protect you from the direct inhalation of viruses, but it’s also like wearing a sweater on your nose,” he mumbled.

Patel concurred and explained that the warmer the intranasal environment can be maintained, the more effectively this innate immune defense mechanism will be able to function. Possibly one more justification to don a mask.

Bleier anticipates the creation of topical nasal medicines based on this scientific discovery in the future. According to him, these novel medications will essentially deceive the nose into believing it has just spotted a virus.

You'll have a lot more hornets flying around in your mucus guarding you because of that exposure.


Sandee LaMotte, CNN News, (2022 December 6th). "Scientists finally know why people get more colds and flu in winter": A chill is in the air, and you all know what that means — it’s time for cold and flu season when it seems everyone you know is suddenly sneezing, sniffling, or worse. It’s almost as if those pesky cold and flu germs whirl in with the first blast of winter weather.

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