The location of pain under the breast is not very accurate, and there are many causes, including pain from somatic diseases, physiologic breast swelling and pain from breast diseases. 1. Physical disease pain: if the position is close to the lower edge of the breast, it may be intercostal neuromuscular pain, it may be costochondritis, or it may be caused by gastric disease or heart disease, it is recommended to do electrocardiogram to see the condition of the heart, and then take a chest X-ray to see the condition of the ribcage. 2. Physiological breast swelling and pain: breast swelling and pain during puberty, girls usually start to develop breasts at menarche, nipple bulge will cause slight swelling and pain. Premenstrual breast pain, there are many women in the menstrual period before the onset of breast fullness, pressure and pain and other symptoms. This is due to the premenstrual period in the body hormone levels rise, the breast tissue edema caused by the period after the pain disappears. 3. Breast disease pain: If there is a regular painful nodule under the breast, it may be breast hyperplasia, which will disappear after menstruation. Pain under the breast may also be caused by mastitis, breast tumors, etc. It is recommended to go to the hospital in time for standardized examination and treatment.