Reference; http://seino-1987.jp/blog/6076.html
Modified and translated by CFJA
Washing your hair in the morning
Would the effects of taking a quick shower in the morning be the same as taking a bath at night? Perhaps to protect the important parts of the body, our hair seems to grow a lot on our head. About 40% of the blood also gathers around and in Eastern Medicine, head is referred to as the gathering place of Yang. So, heading outside when the skin pores are wide open after taking a hot morning shower can cool the head down. Men with a lot of Yang, especially, men who doesn’t have much hair is good at keeping the body. In contrast, especially for women who has more hair compared to men, in general, are weaker at creating body heat. For young women, taking a shower in the morning can cause irregular menstruation and even cause delivery. It will definitely increase the likelihood of you getting a shoulder pain or stiffness.
If you have to take a shower in the morning, we advise you to dry your hair well and relax at home a bit before you go out.