Why Upper Respiratory Infections Are More Common in Colder Temperatures

Scientists uncover a biological explanation

Closeup of woman in hat and scarf blowing nose into a tissue

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Harvard Medical School researchers at Mass Eye and Ear, with colleagues at Northeastern University, have discovered a previously unidentified immune response inside the nose that fights off viruses responsible for upper respiratory infections. Further testing revealed this protective response becomes inhibited in colder temperatures, making an infection more likely to occur.

The new study, published Dec. 6 in the Journal of Allergy and Clinical Immunology, offers the first biological mechanism to explain why cases of the common cold, flu, and COVID-19 are more likely to spike in colder seasons, according to the authors.

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“Conventionally, it was thought that cold and flu season occurred in cooler months because people are stuck indoors more where airborne viruses could spread more easily,” said Benjamin Bleier, HMS associate professor of otolaryngology head and neck surgery at Mass Eye and Ear and senior author of the study.

“Our study, however, points to a biological root cause for the seasonal variation in upper respiratory viral infections we see each year, most recently demonstrated throughout the COVID-19 pandemic.”

First-line defense in the nose

The nose is one of the first points of contact between the outside environment and inside the body, and as such, a likely entry point for disease-causing pathogens.

Pathogens are inhaled or directly deposited (such as by the hands) into the front of the nose where they work their way through the airway and into the body, infecting cells, which can lead to an upper respiratory infection. How the airway protects itself against these pathogens has long been poorly understood.