Nowadays, people are so busy in their life that they even wash hair after ten oclock at night. After washing, they may feel too tired and go asleep quickly with wet hairs. In the next morning, they would feel headache. After scientific research, people find it quite correct.
It is related with the regulation of body temperature. In the metabolic processes, human body constantly produces heat to maintain body temperature, while these heats are conducted to the body surface through blood circulation and continue to diffuse to the outside through radiation, conduction, convection and evaporation.
For people who have strong immunity, their body temperature adjustment is normal and the heating and cooling processes can be balanced through regulation. That is to say, when the body temperature tends to decline, the heat production will increase and the reduction will decrease to maintain the temperature about 37. But to the weak people, their ability of automatic adjustment of body temperature to maintain normal value is weaker. So once the whole body or part body got cold, they will suffer from cold immediately.
After we wash heads with hot water, due to the warm effect, the scalp blood capillary will expand the heat radiated to the surrounding increases. At the same time, the hair is wet after washing, so the evaporation of water brings a lot of heat. Generally speaking, the evaporation of one gram water will take away 500 calories. As heat increases, the body will get cold and the capillaries of upper respiratory tract will contract reflexively. The partial reduction of blood flow and decreased resistance of upper respiratory tract make partial pre-existing viruses or bacteria grow and reproduce quickly, resulting in the respiratory tract infection.
Therefore, it is better not to wash your hairs before going to bed. If you really want to wash, you can wipe you hairs with dry towel or use the hairdryer to blow dry the hair before sleep, so that you will not catch cold so easily.