Scientists May Have Finally Discovered Why People Get Sick in the Winter

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A team of researchers may have finally uncovered why people become far more susceptible to colds and the flu as temperatures fall during winter. The new study, which experts are hailing as a breakthrough, establishes a direct biological link between colder air and a weakened immune response in the nose.

A Timely Discovery

“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,” Zara Patel, a rhinologist at Stanford University who was not involved in the research, told CNN.

The findings arrive at a particularly relevant moment. After being noticeably absent in recent years due to the COVID-19 pandemic, the cold and flu season returned with full force in 2026 as populations once again encountered typical levels of respiratory pathogens.

How Cold Air Weakens Nasal Defenses

Scientists May Have Finally Discovered Why People Get Sick in the Winter In the study, published today in The Journal of Allergy and Clinical Immunology, researchers showed that a temperature drop of just nine degrees Fahrenheit can destroy nearly half of the protective cells that combat viruses and bacteria inside the nostrils.

“Cold air is associated with increased viral infection because you’ve essentially lost half of your immunity just by that small drop in temperature,” Benjamin Bleier, co-author and rhinologist at Harvard Medical School, told CNN.

Important Limitations

The research does carry a significant caveat. “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,” Patel told the broadcaster. Consequently, the results may not fully translate to real-world conditions. “Often the findings of in vitro studies are confirmed in vivo, but not always,” she added.

The Role of Extracellular Vesicles

Scientists May Have Finally Discovered Why People Get Sick in the Winter The team discovered that extracellular vesicles (EVs)—tiny, non-dividing particles released by nasal cells—play a key frontline role. In response to invading pathogens, EVs are released into nasal mucus, where they intercept viruses and bacteria before they can penetrate deeper into the body. Even a modest temperature drop sharply reduces EV production and impairs other defenses, such as protective micro RNA.

According to Bleier, the observed temperature change killed almost 42 percent of EVs, leading to an approximate 50 percent reduction in the immune system’s ability to block infection.

Simple Protection in Cold Weather

Fortunately, effective protection remains straightforward. Keeping nasal passages warm by wearing a mask can help preserve these critical immune functions throughout winter.

“Maybe yet another reason to wear masks!” Patel concluded.