When a woman has her period, the follicles in the ovaries have just started to develop and the amount of estrogen secreted is very small. The epithelium of the vagina is relatively thin and the lactobacilli in the vagina will decrease, which will cause the pH value of the vagina to rise and the acidity of the vagina to decrease, which will easily lead to the growth and reproduction of mold, bacteria and trichomonas in the vagina, so the vulva will feel itchy after the period. As the menstrual period lengthens, the ovaries gradually increase in size and the amount of estrogen secreted will gradually increase, and the itching symptoms will be reduced.