The armpits are called armpits in medicine, and the soreness may be caused by physiological factors such as strenuous exercise or heavy lifting, or it may be caused by pathologic factors such as enlarged lymph nodes and epidermoid cysts. 1. Physiological factors: due to strenuous activities in the shoulder joint or lifting heavy objects and other factors, can lead to local joint muscle strain formed by the soreness, after sufficient rest, the symptoms can usually be gradually alleviated. 2. Enlarged lymph nodes: when there are skin infections, mastitis, breast hyperplasia, etc., it can lead to axillary lymph node enlargement, which can cause soreness and swelling in the armpits, in addition to pain, fever and so on. 2. Epidermoid cysts: When epidermoid cysts are formed in the skin of the armpit, with the increase in the size of the mass, it may compress the axillary artery and axillary nerve in the armpit, which may cause localized soreness, pain and other symptoms. Soreness and swelling of the armpit may also have other causes, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment under the guidance of the doctor.