Zoe Breininger | February 3rd, 2025

Winter has become synonymous with another season, cold and flu. Once November hits and the temperatures dip, we see a spike in the number of cases of the cold, flu, and even COVID-19, but why? Our ability to fight against the pathogens our bodies are exposed to is dependent on many fixed factors — genetics, age, sex, and infection history. But our immunity is also impacted by environmental factors, such as temperature. 

Inside our noses live billions of bacteria that protect our bodies from contracting infections. When the temperature drops and our bodies are exposed to the cold air, those billions of bacteria cannot work as efficiently to protect us. A recent study published in the Journal of Allergy and Clinical Immunology found that reducing the temperature by just 9℉ kills 50% of the billions of protective bacteria that reside in our noses. 

The impact that temperature has on the nose microbiome is significant because the nose is the main entry point for respiratory infections into the body. Additionally, the nose’s response to foreign bacteria is essential for preventing illness and differs from the other immune responses because it occurs before the infection begins. When the nose detects foreign genetic material (from a virus), it creates extracellular vesicles, which are copies of the cells that rest at the lining of the nose. These copies then become the cells that receive the virus, rather than the actual cells that line the nose. When these cells become infected with the virus, they are expelled in mucosal form before the virus has a chance to infect its host (us). 

The nose’s immune response is imperative for preventing illness, but it can be difficult to regulate the temperatures it is exposed to. Masks can be an effective way to mitigate the spread of respiratory illnesses not only because they filter the contents of the air we are breathing in but also because they act as a barrier to cold air. Ultimately, by understanding the role our noses play in preventing illness, we can take proactive steps to prevent illness during the winter season. 

References

Huang, D., Taha, M. S., Nocera, A. L., Workman, A. D., Amiji, M. M., & Bleier, B. S. (2022). Cold exposure impairs extracellular vesicle swarm–mediated nasal antiviral immunity. Journal of Allergy and Clinical Immunology, 151(2). https://doi.org/10.1016/j.jaci.2022.09.037

LaMotte, S. (2022, December 6). Scientists finally know why people get more colds and flu in winter. CNN. https://www.cnn.com/2022/12/06/health/why-winter-colds-flu-wellness/index.html

Pasteur, I. (2018, February 28). Les facteurs qui affectent le plus notre système immunitaire. Institut Pasteur. https://www.pasteur.fr/fr/journal-recherche/actualites/facteurs-qui-affectent-plus-notre-systeme-immunitaire