One condition may be that the skin of the penis is weak, and before sex, the vagina is not sufficiently moistened, the action of sexual intercourse is too violent or rough, causing excessive friction on the penis and the phenomenon of peeling the skin door. Another situation could be that if a woman carries a birth control device with a tail wire, the action during sex is violent and rubs repeatedly with the penis, which may scratch the penis. In the second case, the tail wire should have a proper length and position under the guidance of a doctor. At the same time, it is easy to move gently during sex.