2. Don't sleep with wet hair: If you sleep with wet hair after shampooing at night, the water vapor in the hair will gradually evaporate, taking away the heat of the human body, so that the expanded scalp capillaries will gradually contract due to cold, and the capillaries of the upper respiratory tract will contract conditionally, which will make the body catch cold, local blood supply is insufficient, and the function of the thermoregulation center will decline; In addition, when the pillow is soaked at night to cool down, bacteria and viruses accumulated near the upper respiratory tract will take advantage of it, which will make the shampoo (especially long-haired women) have cold symptoms such as headache, stuffy nose and low fever. Therefore, it is advisable to blow dry your hair with a hair dryer before going to sleep.