What causes pain in the left armpit?

Causes of left armpit pain include: 1. Lymphadenitis: When an infection occurs in a part of the body, nearby lymph nodes may swell and cause pain. The lymph nodes in the left armpit might be affected by infections in the upper limb or chest. 2. Breast-related conditions: Women may experience armpit pain due to breast diseases such as mastitis, fibrocystic breast changes, or breast cysts. These conditions can sometimes involve the lymph nodes in the armpit area. 3. Muscle or joint issues: Overuse or injury, such as a strain in the shoulder or upper arm, may cause pain in the muscles or joints around the armpit. 4. Nerve pain: Compression or damage to peripheral nerves can lead to pain radiating to the armpit area. 5. Tumors: Although uncommon, armpit pain can sometimes be a sign of malignant tumors, such as breast cancer spreading to the armpit lymph nodes, especially if the pain is persistent and without an apparent cause. If armpit pain persists, worsens, or is accompanied by fever, lumps, or other unusual symptoms, prompt medical attention should be sought.