The idea that leaving home with wet hair can cause colds is old, but if you have washed your hair and are in a hurry to leave home, should you really take your grandmother's advice seriously? A study from Cardiff University says constipation is mainly caused by a virus, and cold is just another factor contributing to the onset of symptoms.
The aim of the study was to find out if a cold, wet environment actually activates the virus and all symptoms. 180 volunteers were thus exposed to an extremely cold environment for twenty minutes and then returned to their daily lives, interacting with the rest of the population. In addition to the low laboratory temperature, half of the volunteers also had to set foot in cold water for twenty minutes while the other half remained shod for the same time. There were no symptoms of constipation between the two groups in the first two days, but four to five days later more than half of the group exposed to cold water would have had symptoms of constipation. For these results to make sense it was necessary to find the mechanism that connects cold feet, or for example wet hair, to constipation, and the main finding found by the study was that when the body cools the blood vessels in the nose and throat contract. These same vessels are responsible for the distribution of white blood cells, whose main function is the fight against these infections, so the less white blood cells reach the contracted areas, the more unprotected they will be against the virus. When you are indoors with dry hair, your body tends to reheat, which causes blood vessels to dilate and white blood cells to continue fighting the virus. This is if you have not been exposed to the cold long enough for the virus to multiply, leading to symptoms.
Thus, cold is not exactly the cause of a cold, but a factor that contributes to the activation of symptoms of a virus that was already present in the airways. The topic continues to divide opinions, so there are no direct and definitive links between having wet hair and constipation. Conclusion: There is a real background to the idea that leaving home with wet hair in winter can make someone sick. Although it does not directly cause a cold, it can accelerate the development of one.