Why can't I wash my hair on the fifteenth day of the first day?

The ancients thought that the first month lost and the fifteenth month full moon were the most cloudy days, with women as yin and water as yin. Therefore, washing your hair at this time is most likely to be attacked by yin and evil, leading to colds and head diseases. Modern science has proved that people's immunity will decline when the moon is in deficit and the moon is in surplus, and washing their hair with cold water is really easy to get head diseases. But washing it with hot water and then drying it with a hair dryer is not a big problem.