A lump in the armpit with pressure pain may be caused by inflammation of the lymph nodes or sebaceous cyst infection. If it is lymph node inflammation, it is mostly a bacterial infection, with Staphylococcus aureus being more common, manifesting as red, swollen and painful lymph nodes, which appear enlarged. Oral antibiotic treatment is needed, such as cefixime or cefradine, and also oralloxacin or ciprofloxacin, etc. Generally, the pain can be relieved and the enlarged lymph nodes can subside after treatment. If it is caused by sebaceous cysts, there will be hard masses in the armpits, and there may be black spots on the surface, which need timely anti-infection treatment.