Nipple pain after menstruation may be caused by bra friction, or it may be caused by breast hyperplasia, non-lactating mastitis, and breast cancer. 1. Bra friction: Women who wear poor quality bras or small sized bras after menstruation may have friction on their nipples, which can lead to nipple pain. The symptoms may improve after replacing the underwear with good quality and suitable size. 2. Breast hyperplasia: Breast hyperplasia is considered to be caused by an imbalance in the ratio of estrogen to progesterone or elevated prolactin. Patients will have breast pain, breast lumps, nipple discharge and other manifestations, so patients will appear after menstruation nipple pain. 3. Non-lactating mastitis: The cause of non-lactating mastitis is not yet clear, and it is considered to be related to bacterial infection and breast trauma. Patients may experience breast pain, nipple discharge, nipple inversion and other symptoms, which may manifest as postmenstrual nipple pain. 4. Other: Women with postmenstrual nipple pain are also considered to be caused by breast cancer, breast trauma and other factors. If the nipple pain after menstruation is caused by bra friction, no treatment is needed, and the symptoms will usually improve after changing underwear. If the nipple pain is caused by a disease, you need to consult a doctor to check the cause of the disease, and the doctor will treat the cause of the disease.