Most bumps under the armpit are lipomas if the patient does not experience significant pain and the bumps have a smooth surface, soft texture and good mobility. They usually grow in the fat layer and can be surgically removed. If the bumps are particularly small, they may also be sebaceous cysts or folliculitis. If the bumps are accompanied by pain, they may be swollen lymph nodes in the armpit. The causes of swollen lymph nodes are more varied. On the one hand, they may be caused by inflammation, such as an infection in the tissues associated with the armpit, and the lymph nodes may become reactive and hyperplastic. On the other hand, it may be caused by metastasis of malignant tumors in the breast or other parts of the body. It is recommended to go to a regular hospital for relevant ultrasound, CT or puncture examinations to clarify the diagnosis.