The underarm area contains 20-30 axillary lymph nodes as stated by Healthline.com. The purpose of the axillary lymph nodes are to drain lymph from the breasts, neck, upper arms, and the underarms.
Lymph nodes filter toxic substances from the body. Lymph fluid transports oxygen and nutrients to the cells, and carries away waste products like carbon dioxide, as claimed by the American Cancer Society. According to Medline Plus, lymph nodes make white blood cells, which attack viruses and bacteria. When a virus enters the body, the lymph nodes swell in order to attack the virus and defend the body against infection.