Sometimes hard and sometimes soft nipples may be a normal physiological phenomenon, but it may also be related to breast hyperplasia, acute mastitis and other factors. 1. Normal physiological phenomenon (1) Nipple hardening due to stimulation: Generally, unstimulated nipples are soft, but when the nipple is stimulated by cold, pain, etc., the nipple may become congested and edematous locally, and hardening occurs. (2) Nipple hardening due to sexual arousal: Generally, when sexually aroused, the nipple will also harden, and may be accompanied by swelling of the breasts, accelerated heart rate, etc. These are normal phenomena. These are normal phenomena, when the corresponding stimulation disappears, the nipple will gradually return to soft. 2. Mammary hyperplasia: When the mammary gland is hyperplasia, the normal structure of the mammary gland may be disturbed, which is mainly manifested in the breast swelling, tingling and breast lumps associated with menstrual cycle, etc. Therefore, sometimes the nipples may be felt hard and soft at times. 3. Acute mastitis: It may be manifested as early breast swelling and pain, poor milk secretion, breast lumps, etc. With the development of the disease, the local breast becomes hard and the lumps gradually increase in size. As a result, the nipple may feel hard and soft at times. It is recommended that when nipple discomfort occurs, it is recommended to go to the hospital in time to do a checkup, to clarify the cause of the disease, and then under the guidance of the doctor for treatment.