A lump under the armpit and a little pain are common for the following reasons: First, there is a lump growing under the armpit, such as sebaceous gland cyst, lipoma, fibroma, etc. You need to go to the hospital to improve relevant examinations, such as color ultrasound or CT for clarification. Second, it may be caused by lymph node enlargement. There are many causes, such as bacterial infection, viral infection, tuberculous infection, autoimmune system disease, blood system disease, and even lymph node metastasis of malignant tumors. You need to go to the hospital to improve relevant examinations, such as blood routine, C-reactive protein, color ultrasound or CT. Sometimes you also need to do lymph node biopsy or excision biopsy to clarify the nature. Third, it may be caused by hyperplasia of accessory milk.
