The appearance of a mass in the armpit with pressure pain may be caused by lymph node inflammation or sebaceous cyst infection. If it is lymph node inflammation, it is mostly bacterial infection, Staphylococcus aureus is more common, manifested by redness, swelling and pain in the lymph nodes, and the appearance of lymph node enlargement. Oral antibiotic treatment is needed, such as cefixime or cefradine, or oral clofloxacin or ciprofloxacin, etc. Generally, the pain can be relieved after treatment, and the enlarged lymph nodes can also subside. If it is caused by sebaceous cysts, there will be hard lumps in the armpits, and there may be black spots on the surface, which need timely anti-infective treatment. If the anti-infective treatment is not timely, there may be abscess formation, which needs to be cut to drain out the pus, and the wounds should be changed regularly.