As the winter chill sets in, many people believe that the cold itself is to blame for the surge in colds and flu. However, modern research has shown that the connection between cold weather and illness is more nuanced than the common assumption that cold air directly causes disease.
Contrary to popular belief, cold temperatures do not actually cause infections. Instead, they influence a combination of biological, environmental, and social factors that make people more vulnerable to respiratory illnesses, especially during the colder months.
Viruses such as rhinoviruses, which cause the common cold, and influenza viruses spread from person to person through respiratory droplets or physical contact, regardless of the outdoor temperature. However, rates of respiratory infections consistently increase during the winter season in many parts of the world.
This seasonal pattern is partly due to the way that cold temperatures and low humidity affect viruses in the environment. Research shows that many respiratory viruses, including influenza viruses and coronaviruses, survive longer and remain infectious for extended periods in cold, dry conditions. Dry air also causes tiny droplets released when people breathe, talk, cough, or sneeze to evaporate quickly, creating smaller particles that stay suspended in the air longer, increasing the chances of others inhaling them.
Cold air can also affect the body’s defence mechanisms against infection. Breathing in cold air lowers the temperature inside the nose and airways, which can trigger vasoconstriction, or the narrowing of blood vessels, reducing blood flow to the tissues. This can weaken local immune responses that normally help detect and eliminate viruses before they cause infection.
Seasonal changes in human behaviour and indoor environments also play a major role. Cold weather encourages people to spend more time indoors, often in close contact with others. Crowded spaces with poor ventilation allow virus-containing droplets to build up in the air, making transmission between people more likely. Additionally, reduced sunlight exposure during winter can lead to lower production of vitamin D, which is involved in regulating immune function.
While cold weather can be especially challenging for people with existing respiratory conditions, such as asthma or allergic rhinitis, the evidence clearly shows that cold temperatures do not directly cause colds or flu. Instead, cold weather acts as a risk amplifier, creating conditions that help viruses survive, spread, and overcome the body’s defences.
By understanding the nuanced relationship between cold weather and illness, we can focus on more effective strategies for prevention, such as improving indoor ventilation, maintaining adequate humidity, and supporting immune health through measures like ensuring adequate vitamin D levels. Public health messages that emphasize how viruses spread through contact and respiratory droplets, rather than reinforcing the myth that cold exposure alone causes sickness, can also be more effective in helping people stay healthy during the winter months.
