There are countless sweat glands and sebaceous glands on the scalp, and they often secrete sweat and grease. Due to it being covered by hair, it is difficult for heat to dissipate and secretion will merge easily with dust and dandruff, causing growth of bacteria and accumulation of filth, damaging hair follicles and hair quality. The long-term exposure of hair to air allows bacteria within the air to come into contact with secretions from the sebaceous glands of the head, creating dandruff and dirt in the process. Therefore we have to comb and wash our hair regularly for it to stay healthy, shiny and elastic (those with oily scalps should wash their hair every day and those with very little oil generated on their scalp are to wash their hair 2 to 3 times a week at least).
Note: It is most appropriate to wash your hair with warm water – if the water temperature is too low, it would be difficult to remove grease,and if the temperature is too high, it will damage the scalp, worsening the dandruff problem. For people who experience hair loss and use either hot or cold water to wash their hair, it is kind of a negative stimulus for both the hair and scalp, worsening the problem of hair loss. After washing the hair, it is best to let it dry naturally.