Bumps under the armpit are commonly sebaceous cysts, lipomas, enlarged lymph nodes, folliculitis, and paronychia. First, sebaceous cysts are located in the subcutaneous shallow, with clear boundaries with the surrounding tissues, and small black concave lines can be found on the local skin surface, which advocate surgical removal. Secondly, lipoma. It is located in the subcutaneous fat layer, with clear boundary, soft texture, no pain, and usually not infected, and surgical excision is preferred. Third, enlarged lymph nodes, this kind is mostly caused by trauma to the surrounding tissues. If it is not painful, but hard, it needs to be noted as a tumor. Fourth, parammary glands. Some women can have parammary glands, which are characterized by poorly defined borders and soft masses, mostly bilateral, and some patients can have swelling and pain at the time of menstruation. Fifth, folliculitis. It starts as a red papule and gradually evolves into a papule-like pustule, isolated and scattered, with mild self-induced pain. In adults, it mainly occurs on hairy areas, while in children it is more common on the head. The above content is for reference only, please refer to the doctor’s guidance for specific medication and treatment.