Why does the girl's vulva and thigh root turn black

The blackening of the vulva and the base of the thigh marks the beginning of sexual maturity, because these areas do not darken until puberty, that is, before the girl's menstruation. only after menstruation do the ovaries begin to periodically secrete estrogen and progesterone, and the skin color of these areas will darken under the action of estrogen. This is a normal physiological phenomenon, as long as in daily life to keep the vulva local clean, clean the vulva once a day, change underwear can be, in addition to menstruation is also recommended to change sanitary napkins frequently, so as to reduce the chance of reproductive tract infection. And women after pregnancy vulva, thigh roots, and breast nipples, areola will show coloring phenomenon