Painful swelling on one side of the armpit after menopause is considered to be related to breast fibroadenoma, breast cancer, lymphadenitis, lymph node enlargement and other diseases. 1. Breast fibroadenoma: this is a benign disease that occurs in the breast, for postmenopausal women, it may be adhered to the surrounding tissues, which may cause pulling and pain in the armpit. 2. Breast cancer: Breast cancer is a malignant disease, due to the rapid growth of cancer cells, it may metastasize to the lymph nodes in one side of the armpit, which may cause lymph node enlargement and pain and discomfort. 3. Lymphadenitis: If women have inflammatory diseases such as pneumonia and otitis externa, the inflammatory factors will spread with the lymphatic vessels, and pain and discomfort will occur when patients have axillary lymphadenitis. 4. Enlarged lymph nodes: If women have lung cancer, lymphoma and other diseases, and if they metastasize to the axillary lymph nodes, the enlarged lymph nodes will also cause pain and discomfort. For menopausal women with pain in the armpit, it is recommended to go to regular hospitals to improve the breast ultrasound, CT and other related examinations, to clarify the cause of the disease and then actively treat it under the guidance of the doctor.