There are a few possibilities for what could be causing the lymph nodes in the groin to be swollen, such as an injury or infection in the lower extremities, pelvis or groin. The more severe possibilities are skin or testicular cancer and lymphoma.
Lymphoma is a cancer that infects the lymphocytes, a type of white blood cell. Lymphedema, also known as lymphoedema, occurs when the lymph fluid builds up in the spaces between cells and causes swelling. Genital herpes can also cause swollen or sensitive lymph nodes during an outbreak. People experiencing any signs of painful swelling should contact a physician immediately.