The main reason for the white sweat hair on the arm is the following: 1, vitiligo patients due to local melanin deficiency, local melanin secretion reduction, sweat hair root can not absorb melanin from the pores and lead to white sweat hair, in addition to white sweat hair, the local skin is also white. 2, into old age body parts function began to decline, the body melanocyte secretion reduction and lead to the arm or other parts of the white White sweat hair.