Pain in the inner armpit arm is often caused by the following reasons: First, skin infection, when the skin is infected, pain can occur, while local redness and swelling can occur, and even fluid exudation. This requires active topical medication and, if necessary, oral antibiotics with treatment. Second, it may be caused by the growth of swellings, such as sebaceous cysts, lipomas, fibroids and so on. You need to go to the hospital to check the ultrasound for clarification, and if necessary, surgery to remove. Third, it may be caused by swollen lymph nodes, which also need to go to the hospital for surgical examination, if necessary, the lymph nodes need to be removed, or with the drug for treatment. Fourth, some patients may have thrombosis, such as venous thrombosis or arterial thrombosis. It is necessary to go to the hospital to check the ultrasound of blood vessels and coagulation function. If this is the case, medication, surgery or interventional treatment is needed.