The real reason you're more likely to get a cold in the winter

A child unsuitably dressed for winter weather will often be told by a scolding mother that if they go outside like that, they will “catch a death of cold”.

Now, it seems there may be truth to the old wives tale with scientists proving that cold weather does make us more susceptible to catching a bug.

A study found a never-seen-before immune response inside the nose is suppressed by colder temperatures, making people more prone to catching colds.

Scientists say this finding offers the first biological evidence for why respiratory illnesses like colds, flu and Covid are more likely to spike when the temperature drops.

The upper respiratory tract (nose, mouth and throat) is the primary way people get infected through either inhaling the bug or depositing it with their hands.

Immune response blocked in cold conditions

Researchers at Boston's Mass Eye and Ear hospital and Northeastern University in the US have discovered a previously unidentified immune response inside the nose that fights off viruses responsible for upper respiratory infections.

Further testing revealed this response becomes blocked in cold conditions.

"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 Dr Benjamin Bleier, director of Otolaryngology Translational Research 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."

The team found in 2018 that there is an innate immune response which is triggered when a bacterium is inhaled through the nose.

Cells in the front of the nose pick up signs of the bacteria and in response pump out billions of tiny fluid-filled sacs called extracellular vesicles (or EVs) as a defence mechanism.

These defensive packages also recruit protective proteins which have antimicrobial properties to further bolster defences.

Fresh work from the same team published this week looked at if viruses also triggered a similar reaction.

Aim is to replicate findings with other diseases

They found that the body’s immune system makes EVs and the end result is similar, but the process by which it occurs is different to bacterial infections.

The team found the EVs act as decoys, attracting the virus to them and therefore preventing infection.

But when the team lowered the temperature to winter levels of sub-five degrees Celsius they found that this decoy-making mechanism was less effective.

The number of virus-fighting EVs dropped by 42 per cent, the scientists found, at sub 5°C temperatures compared to room temperatures.

"Combined, these findings provide a mechanistic explanation for the seasonal variation in upper respiratory infections,” Dr Di Huang, first author and a research fellow at Mass Eye and Ear and Northeaster, said.

The researchers found the system to be less effective in fighting off coronaviruses and rhinoviruses, the two main families of common colds, when the temperature dives.

They now hope to replicate the findings with other diseases in the future. The new study is published in The Journal of Allergy and Clinical Immunology.