There are black hairs in the pores of the back, a cause is a normal physiological phenomenon, may be in the youth development period of adolescents, both men and women can, androgen and the body estrogen, progesterone regulation metabolic level is unstable, easy to appear inside the pores of the back of the sweat hair is more vigorous. If it is not very serious, there is no need to carry out special treatment treatment, pay attention to the local cleanliness and hygiene. Another factor is common acne, which may be prone to chronic inflammatory clinical manifestations of the sebaceous glands of hair follicles.