London: Spending time outdoors on chilly days is often blamed for coughs, colds, and runny noses, but experts say cold weather itself is not the direct cause. While respiratory infections are more common in winter, this is largely due to how people behave during colder months rather than the temperature alone.
John Tregoning, Professor of vaccine immunology at Imperial College London, says the link between cold weather and catching a cold is ‘almost certainly correlation, not causation.’
One small contributing factor is sunlight, as ultraviolet (UV) light can kill viruses. For example, sneezing outdoors in summer may expose viral droplets to sunlight, which can deactivate the virus, while faster evaporation causes the droplets to dry out. In winter, this protective effect is reduced.
However, the main driver of winter illness is behavioural. In colder weather, people tend to spend more time indoors, often in poorly ventilated spaces and in closer contact with others, creating ideal conditions for viruses to spread.
Evidence from the COVID-19 pandemic clearly demonstrated how important human contact is in virus transmission. During lockdowns, many common viruses largely disappeared because people were not interacting, and one strain of influenza even became extinct due to a lack of spread.
Rhinovirus and RSV
Different cold and flu viruses also peak at different points during the winter season. Tregoning, who is also the author of Live Forever? A Curious Scientist’s Guide to Wellness, Ageing and Death, explains that rhinovirus, a leading cause of the common cold, tends to spike when children return to school and spread germs in small classrooms. Respiratory syncytial virus (RSV), another cold virus that can be particularly serious for older people and babies, typically peaks around the new year.
That said, extreme cold can have some effect on susceptibility to infection. If someone is exposed to cold for prolonged periods, loses calories, and becomes exhausted, their immune defences may weaken, making them more prone to illness. Studies also show that rhinoviruses grow slightly better at cooler temperatures and that the body’s ability to defend against viruses is somewhat reduced in colder air.
The most effective protection against winter respiratory infections remains vaccination, particularly for viruses such as influenza and RSV. Tregoning notes that vaccines do more than just prevent infection; they also provide broader health benefits, including reducing the risk of heart attacks.
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