Why Do We Catch More Colds in Winter?

Every autumn, it begins. A colleague sniffs, a child comes home from school with a cough, and soon half the household is reaching for tissues. Parents and grandparents have warned for generations: wrap up, or you’ll catch your death of cold.

They were partly right, though not for the reason they thought. Cold weather doesn’t cause colds. Viruses do. But winter gives those viruses a helping hand in several ways.

What causes a cold

The common cold is an infection of the nose and throat caused by a virus. More than 200 different viruses can cause one. The most common are rhinoviruses, from the Greek word for nose. Others include some coronaviruses, adenoviruses and respiratory syncytial virus (RSV).

Adults typically catch two or three colds a year, and young children more. You catch a cold by breathing in tiny droplets from an infected person’s cough, sneeze or breath, or by touching a surface with the virus on it and then touching your nose or eyes.

Cold weather doesn’t cause colds. Viruses do. But winter gives them a helping hand.

Why winter helps viruses

1. We spend more time indoors, together

In cold weather, people stay inside, close together, with windows shut and less fresh air. Children are back at school after the summer holidays, mixing with dozens of others every day. All of this gives viruses more chances to pass from one person to the next. Better ventilation, such as opening windows, dilutes virus particles in the air.

2. Dry air helps some viruses survive

Winter air is often dry, both outdoors and inside heated buildings. Research on flu viruses suggests they survive and spread better in cold, dry conditions. A well-known 2007 study by Anice Lowen and colleagues found that flu spread more easily between guinea pigs in cold, dry air than in warm, humid air. Later research linked flu seasons in temperate countries with periods of low humidity.

3. A cold nose fights viruses less well

Breathing cold air cools the inside of your nose. In a 2015 laboratory study, researchers at Yale University found that rhinoviruses grew better at the cooler temperature found inside the nose (about 33°C) than at core body temperature (37°C), partly because the cells’ defences worked less well when cooler. A 2022 study by researchers in Boston found that cells lining the nose release tiny particles that help trap viruses, and this defence weakened when the inside of the nose was cooled.

These findings come mainly from cells and animals, so they don’t prove exactly how much each factor matters in people. But they help explain why a cold nose may be more vulnerable.

4. Less sunlight, less vitamin D

In winter, especially far from the equator, the skin makes less vitamin D because there is less strong sunlight. Low vitamin D has been linked with more respiratory infections. A 2017 review of 25 trials, led by Adrian Martineau, found that vitamin D supplements slightly reduced the risk of respiratory infections, with the clearest benefit in people who were very low in vitamin D to begin with.

What about warm countries?

In the tropics, where there is no cold winter, colds and flu happen all year round, and flu often peaks during the rainy season, when people also spend more time indoors together. This supports the idea that how people gather, not just temperature, plays a big part.

How to lower your chances

• Wash your hands often with soap and water, especially before eating and after being out.
• Try not to touch your eyes, nose and mouth with unwashed hands.
• Let fresh air in. Even opening a window for a few minutes helps.
• Stay home when you’re ill, if you can, and cough or sneeze into a tissue or your elbow.
• Get a flu vaccine if it’s recommended for you. There’s no vaccine for the common cold, but flu can be much more serious.
• Look after the basics: sleep, regular activity and a balanced diet all support your immune system.

When to see a doctor

Most colds get better on their own within 7 to 10 days, though a cough can last longer. Rest, fluids and simple painkillers can help with symptoms. Antibiotics don’t work against viruses.

See a doctor if symptoms last more than three weeks, get suddenly worse, or if you have difficulty breathing, chest pain, a very high temperature, or a long-term condition such as asthma or heart disease. Seek advice quickly for babies and young children with a high temperature.