Small hard bumps under the armpits may be dermatofibroma, sebaceous cysts, swollen lymph nodes, etc., patients should consult a doctor in time to clarify the cause of the disease after treatment. 1. Dermatofibroma: a kind of benign tumor in the dermis caused by fibroblasts or tissue proliferation, occurring in the armpits will be manifested as hard bumps in the armpits, and part of the population may be accompanied by itching, which generally does not require any special treatment, and can be surgically removed if necessary. 2. Sebaceous cysts: hard bumps in the armpits may be sebaceous cysts formed by sebum stagnation caused by the blockage of sebaceous gland ducts in the skin, and there will be redness, swelling and fluctuating sensation when secondary infection occurs, which can be surgically excised in the non-infectious period. 3. Enlarged lymph nodes: If the patient has painful hard lumps in the armpits and there are foci of infection in the nearby tissues, it should be considered as enlarged lymph nodes, and the primary cause of enlarged lymph nodes, such as infection, should be treated at this time. All of the above treatments and procedures should be carried out under the supervision of a doctor.