Hidden pain in the left armpit near the breast may appear as a symptom of paratesticular breasts, or it may be a symptom of certain diseases, such as breast hyperplasia, axillary lymphadenitis, etc., and you should consult a doctor in time to find out the cause of the disease. 1. Associate breasts: The main manifestation is that with the development of puberty, the associate breasts are gradually enlarged, and increase significantly during menstruation, pregnancy and breastfeeding, and some of the patients are accompanied by pain. 2. Mammary hyperplasia: It is mainly manifested as breast pain and the pain is regular, and there are also breast nodules or lumps, and some of them can be combined with nipple discharge. 3. Axillary lymphadenitis: mainly manifested by enlarged lymph nodes and pain, in severe cases, there may be multiple enlarged lymph nodes, which may merge to form a larger lump, aggravated by pain, redness and heat of the surface skin, accompanied by systemic symptoms, such as fever, malaise, etc. Meanwhile, skin diseases, traumas, and other diseases may also be present. Meanwhile, skin disease, trauma, soft tissue contusion, heart disease, digestive system disease, lung disease, costal cartilage disease may be manifested as pain on the left side close to the breast position, which needs to be carefully identified. In addition to the above factors, it cannot be ruled out that it is caused by other factors. When the pain is persistent, you should consult a doctor who can identify the cause and give you targeted treatment.