Painful and enlarged underarm lymph nodes are mostly considered as lymph node infection, tumor metastasis and other diseases. 1. Lymph node infection: after lymph nodes are infected by bacteria, resulting in lymph node hyperplasia, accompanied by pain, swelling and other symptoms. 2. Tumor metastasis: such as breast tumor, axillary lymph node metastasis will occur in the late stage, resulting in lymph node enlargement, pain and other symptoms. It is suggested that patients should improve ultrasound, nuclear magnetic examination, etc., and then undergo surgical resection or radiotherapy according to the stage of the disease. 3. Reactive hyperplasia: common in serum sickness and serum sickness-like reaction, systemic lupus erythematosus rheumatism, etc. Whether the condition is serious or not should be analyzed with the patient’s individual situation. However, regular treatment under the guidance of a doctor can also control and stabilize the condition. Painful and enlarged axillary lymph nodes are also seen in other causes, should be timely consultation, complete ultrasound, MRI and other tests, according to the cause of the appropriate treatment program, so as not to delay the condition.