“You’ll get a cold!” – our grandmothers always warned us, as soon as we dared to leave the house on a cold day without drying our hair. For centuries, in many parts of the world, the idea has been that you can catch a cold if you are exposed to cold temperatures, especially when you get wet. English even uses homonyms to describe the combination of sore throat, runny nose and cough that you encounter when you catch a cold: cold – cold / cold, chill – chills / cold.
But any doctor will assure you that a cold is caused by a virus. So, if you don’t have time to dry your hair and it’s time to run out of the house, should you worry about your grandmother’s warnings?
Studies in and around the world have found a higher incidence of colds in the winter, while warmer countries such as Guinea, Malaysia and the Gambia have recorded peaks during the rainy season. These studies suggest that cold or wet weather causes colds, but there is an alternative explanation: when it’s cool or rainy, we spend more time indoors in close proximity to other people and their germs.
So what happens when we get wet and cold? The scientists set up experiments in the laboratory where they lowered the body temperature of volunteers and deliberately exposed them to the common cold virus. But overall, the results of the studies were inconclusive. Some studies have shown that groups of participants exposed to cold temperatures were more prone to colds, others were not.
However, the results of one, carried out according to a different methodology, suggest that the fact that cooling may indeed be associated with a cold.
Ron Eccles, a director in Cardiff, UK, wanted to find out if cold and damp activate the virus, which then causes cold symptoms. To do this, people were first placed in a cold temperature, and then they returned to normal life among people – including those who had an inactivated cold virus in their bodies.
Half of the participants in the experiment during the cooling phase for twenty minutes sat with their feet in cold water, while the others remained warm. There was no difference in cold symptoms reported between the two groups in the first few days, but four to five days later, twice as many people in the cooling group said they had a cold.
So what’s the point? There must be a mechanism by which cold feet or wet hair can cause a cold. One theory is that when your body cools down, the blood vessels in your nose and throat constrict. These same vessels carry infection-fighting white blood cells, so if fewer white blood cells reach the nose and throat, your protection against the cold virus is reduced for a short time. When your hair dries out or you enter a room, your body heats up again, blood vessels dilate, and white blood cells continue to fight the virus. But by then, it may be too late and the virus may have had enough time to reproduce and cause symptoms.
Therefore, it turns out that cooling itself does not cause a cold, but it can activate a virus already present in the body. However, it is worth bearing in mind that these conclusions are still controversial. Although more people in the cooling group reported that they had come down with a cold, no medical tests were done to confirm that they were indeed infected with the virus.
So, perhaps there was some truth in Grandma’s advice not to walk down the street with wet hair. Although this will not cause a cold, it can trigger the activation of the virus.