Having a period is not an indication of running out of milk. There is no direct link between milk production during breastfeeding and the onset of menstruation. The production of milk is due to the increase of estrogen and placental lactogen during pregnancy, which promotes the development of the mammary glands and the formation of milk. After delivery, the cells of the breast gland will start to produce milk under the action of lactogen. Therefore, there is no direct relationship between menstruation and milk secretion, and it is not true that there will be no milk if you have menstruation. Women may have irregular menstrual flow after delivery because of the change of hormone level, but at least after the puerperium, menstruation may come normally. If a woman is exclusively breastfeeding, she may have her period about six months after delivery because her body has higher levels of lactogen, which can inhibit ovulation. In contrast, women can breastfeed for up to two years or even longer, and it is a normal situation to have menstruation during the breastfeeding phase. Milk production is closely related to a woman’s physical condition after giving birth, and whether she has adequate nutrition, good sleep, and a pleasant mood can affect milk production. Babies sucking on the nipple can also produce a nipple reflex, which releases contractin, an important factor in promoting milk production from the nipple, so sucking is an important condition for constantly emptying the breast and promoting breast lactation.