The common causes of axillary bulges are lipomas and parametrium, etc.: 1. Lipomas: localized fatty tissue hyperplasia forming a lipoma, which is a relatively common benign clinical disease, the size and specific nature of the lipoma can be clarified through ultrasound examination. 2. Parametrium: Young female patients may have axillary parametrium, which may also appear as a local bulge, and is caused by congenital abnormal breast development. If the skin follicle is infected or the sebaceous gland is infected, it will also appear to be bulging.