Hidden pain in the left armpit is usually due to the following reasons:1. Commonly caused by lymphadenitis, the left armpit lymph nodes are more developed and abundant, so lymphadenitis, lymphadenitis is the most common.2. Cellulitis and connective tissue inflammation caused by infection in the left armpit will also have hidden pain in the left armpit.3. Diseases of the breast system, such as acute mastitis, lobular hyperplasia and malignant breast tumors will also appear in the left armpit.4. Heart disease, coronary artery insufficiency, acute coronary syndrome, acute myocardial ischemia, acute pericarditis, etc. will also appear in the left armpit. Breast system diseases, such as acute mastitis, breast lobular hyperplasia, and malignant breast tumors can also cause pain in the left armpit.4 Heart disease, coronary artery insufficiency, acute coronary syndrome, acute myocardial ischemia, acute pericarditis and other conditions, can also be caused by ischemic pain in the left armpit, accompanied by chest pain, tightness in the chest, shortness of breath, and other clinical symptoms.5 Paramilitary breasts and benign connective tissue hyperplasia can also lead to hidden pain in the left armpit.