What causes a lump under the armpit and what should I do?

　　A lump under the armpit may be caused by pubertal changes, the menstrual cycle, lymph node enlargement, mastitis, or sebaceous cysts. Management options include observation, medication, or surgical treatment.

　　1. Pubertal changes: Fluctuations in hormone levels during puberty, especially increased sex hormones, may stimulate lymphoid hyperplasia, causing slight enlargement of lymph nodes under the armpit. This condition is usually painless and stable in size. Generally, no special treatment is required, and in most cases, it resolves on its own after puberty.

　　2. Menstrual cycle: During the female menstrual cycle, especially near the onset of menstruation, changes in estrogen and progesterone levels may stimulate reactive hyperplasia of lymphoid tissue, leading to slight enlargement of the axillary lymph nodes. Usually, no special management is required, and symptoms naturally subside after menstruation.

　　3. Lymphadenopathy: When the body is affected by infections, inflammation, or other diseases, lymph nodes under the armpit may swell as part of the immune response to abnormal conditions in the body, possibly accompanied by pain or tenderness. It is recommended to follow medical advice and use medications such as amoxicillin capsules, cefixime dispersible tablets, or cefalexin injection for treatment.

　　4. Mastitis: Weakened immunity, milk stasis, breast trauma, and other factors may lead to mastitis, which can trigger an immune response in the axillary lymph nodes, causing lymph node swelling, possibly accompanied by breast pain, nipple discharge, or breast lumps. It is recommended to use medications such as minocycline hydrochloride capsules, bromocriptine mesylate tablets, or Rupixiao capsules under a doctor's guidance to alleviate discomfort symptoms.

　　5. Sebaceous cyst: The sebaceous glands under the armpit may become blocked, preventing normal sebum drainage, leading to sebum accumulation under the skin and the formation of a cyst. These cysts are usually round, soft in texture, and sometimes the contents can be felt. Generally asymptomatic, but when the cyst enlarges or becomes infected, pain, redness, or swelling may occur. Small cysts can be observed without intervention, but if they enlarge or become infected, surgical excision under medical guidance is recommended. Surgical options include incision and drainage or cyst excision.

　　If discomfort symptoms occur, it is recommended to seek timely medical consultation, clarify the condition, and follow medical advice for treatment to avoid delaying the illness.