The more common clinical causes of axillary swelling and pain on pressure include the following: an infection of the skin follicles; and a secondary infection of the sebaceous gland cysts, which causes swelling and pain and lumps in the deep axillae. There are also some lymph node inflammation caused by these are the more common clinical causes. The skin follicle infection is relatively common, mainly because the hair follicle sweat gland is more developed, after being infected by the body surface skin bacteria, when the body’s immunity is relatively low, it is easy to cause bacterial infection, appearing red, swollen and painful. In addition, due to the low immunity of the body, it is also easy to cause bloodstream infection, resulting in reactive hyperplasia of the axillary lymph nodes and inflammation of the axillary lymph nodes, all of which will appear swollen and painful. Therefore, if you have swelling and pain in the armpit, you must go to a regular hospital and find a specialist to do a detailed examination. Generally, you can find the cause of the swelling and pain through color ultrasound investigation or review of blood tests, and carry out systematic and standardized treatment for the cause.