Does cold weather give you a cold? Not directly. Colds are caused by viruses. Without a virus, you will not catch a cold, even in very cold places.

But cold weather helps viruses. One common cold virus grows better in a cool nose. Dry winter air also helps viruses spread.

And in winter, people stay together inside with the windows closed. So cold weather is a helper, and the virus is the cause.

Science teachers often say that colds are caused by viruses, not by cold weather. That is true, but recent research shows that cold weather can act as an accomplice. In a 2015 study, researchers at Yale University found that rhinovirus, a common cold virus, grew better at 33°C, close to the temperature inside the nose, than at 37°C. At the lower temperature, the cells' alarm system against viruses worked less well.

A 2007 study with guinea pigs also showed that flu viruses spread more easily when the air was cold and dry. In addition, people in winter tend to gather in closed rooms with poor ventilation. So the saying "cold weather gives you a cold" is partly right.

The English word "cold" itself links chilly weather and illness, yet biology teaches that colds are caused by viruses, not by low temperatures. Recent research suggests the truth lies in between: cold is not the culprit, but it may be an accomplice. In a 2015 study using mouse airway cells, Ellen Foxman, Akiko Iwasaki and colleagues at Yale found that rhinovirus replicated more readily at 33°C, close to nasal temperature, than at 37°C, partly because cells' antiviral alarm signals, such as interferons, were weaker at the cooler temperature.

Later experiments with human nasal tissue suggested that cooling also reduces tiny decoy particles that nasal cells release to trap viruses. Environmental factors add to the effect. A 2007 study in guinea pigs found that influenza spread more readily in cold, dry air, and in winter people crowd into poorly ventilated rooms. These mechanisms come largely from cell and animal studies, so their effect on infection rates in humans is not yet known.

A 2005 British experiment in which people who chilled their feet reported more cold symptoms relied on self-reported symptoms without confirming infection. The saying is therefore wrong as an explanation of cause but partly right as a practical rule.