Armpit hair is the manifestation of human secondary sex characteristics, with the role of reducing friction, regulating the role of immunity, promote sweating, but also has a certain aesthetic effect. 1. Reduce friction: arm movement will make the armpit around the skin inevitably produce friction, if the friction is too long, too heavy will damage the skin. Armpit hair in its “middle”, precisely to ease the skin friction, protect the armpit skin from abrasions, so the role of armpit hair should not be taken lightly. 2. Regulate the role of immunity: human armpit hair can play a role in shielding and protecting the human skin, so that the skin is not subject to foreign bacteria, dust and other invasions, the “enemy” in the skin outside the door. 3. Promote sweating: adolescent girls, teenage sweat glands began to active, armpit is also an active part of the armpit, armpit hair can increase the surface area of the armpit, accelerate the speed of evaporation, so that the armpit to keep dry. But the armpit hair due to sweat glands, sebaceous glands and sweat glands are more developed, can also cause corresponding diseases, such as armpit hair ringworm or folliculitis, as well as sweating, so need to keep the local clean, if uncomfortable, consult a doctor in time.