A vague pain in the outer left breast, without hard lumps, may be a physiological reaction, more common at the onset of menstruation; after the end of menstruation has been painful, should be wary of mastitis, breast hyperplasia due to. 1. Physiological reaction: most women will experience breast pain without hard lumps during their menstrual period, which is related to the change of estrogen level in the body. Usually when the menstrual period is over and the hormone level returns to normal, the symptoms of breast pain will gradually decrease and disappear. 2. Mastitis: Acute mastitis, acute suppurative mastitis, can cause breast swelling and pain, redness and swelling and other symptoms, mainly due to inflammation stimulation of the glands, resulting in local oozing fluid, so that the breast tissue necrosis caused by breastfeeding, more common during the breastfeeding period. 3. Mammary hyperplasia: usually related to the growth and development of the mammary glands due to elevated prolactin, there will be obvious pain during the development of the glands. If breast disease is suspected, it is recommended to carry out diagnosis and analysis through breast ultrasound and breast pathology examination to clarify the type of breast disease before carrying out treatment.