Why can’t women wash their hair at night?

　   After washing your hair at night, it would be best if you allow enough time to dry your hair before going to bed. But sometimes I'm so busy that I don't wash my hair until after 10pm. After washing my hair, I feel so tired that my eyelids are so heavy that I can't open my eyes, so I fall asleep before my hair is dry. If you do this, the older generation will say that you will have headaches in the future. In fact, after modern scientific research, people have found that this is not unreasonable.

　　We must know that during the metabolic process, the human body always continuously generates heat to maintain body temperature. This heat is also conducted to the surface of the body through blood circulation, and is continuously dissipated to the outside world through radiation, conduction, convection, and evaporation.

　　People with strong body resistance have normal body temperature regulation function. Through regulation, the two processes of heat production and heat dissipation are balanced. That is, when the body temperature tends to drop, heat production increases and heat dissipation decreases, so that the body temperature is still maintained at around 37°C. However, for people with weak body resistance, their ability to automatically regulate body temperature and maintain normal body temperature is poor, so when the whole body or a certain part of the body catches cold, it is easy to cold。

　　After we wash our hair with hot water, due to the warming effect, the scalp capillaries expand, and the body radiates more heat to the surroundings. At the same time, because the hair is wet after washing, a lot of water evaporates, and a lot of heat is taken away. Generally, 500 calories are taken away when one gram of water evaporates. Due to the increase in heat dissipation, the body is exposed to cold, which reflexively constricts the capillaries of the upper respiratory tract, reduces local blood flow, and lowers the resistance of the upper respiratory tract. This allows local viruses or bacteria that have already existed to take advantage of the weakness, grow and reproduce, and cause upper respiratory tract infections, resulting in cold symptoms such as runny nose, nasal congestion, headache, and even fever wait.

　　And if you fall asleep with your hair wet, the regulatory function of the body temperature regulation center will be low at this time, making you more likely to catch a cold.