Armpit generally refers to the armpit, there is a bulge under the armpit, the common causes are enlarged lymph nodes, lipoma, etc., you should consult the doctor in time to find out the cause of the disease. 1. Enlarged lymph nodes: enlarged lymph nodes mostly occur after inflammatory reaction caused by bacteria and other infections, and may also be caused by tumor and other factors. Lymph node enlargement caused by infection usually has pressure and pain, smooth surface and no adhesion. Lymph nodes caused by tumor are usually progressively enlarged, hard, without obvious pressure and pain, and adhered to the surrounding tissues. 2. Lipoma: Lipoma is a common benign soft tissue tumor, usually a painless lump of small size. Due to the slow growth of lipoma, there is usually no uncomfortable symptom, when the tumor is too big, it can form a bulge and press the surrounding tissues to produce pain, which needs to be surgically removed. The appearance of bulging bags under the armpit, should be timely consultation, improve the relevant examination, to clarify the cause of the disease, if necessary, targeted treatment.