There are many causes of swollen lymph nodes under the armpit, so how to treat swollen lymph nodes under the armpit should be specifically analyzed according to the specific cause. It can be a benign disease that causes swollen lymph nodes in the armpit, such as acute mastitis, which should be treated promptly with antibacterial therapy. It can also be a malignant disease that causes swollen lymph nodes in the armpit, the most common one being breast cancer. If the swollen axillary lymph nodes are caused by breast cancer, timely treatment should be provided, such as surgical excision, radiotherapy, chemotherapy and some targeted therapies. In short, the treatment should be based on the specific cause of the disease.