A hard substance in the left groin may be caused by severe constipation, enlarged lymph nodes, inguinal hernia, etc. 1. Severe constipation: When constipation is severe, feces can collect in the rectum and the end of the sigmoid colon, forming a hard lump in the left groin. 2. Enlarged lymph nodes: A hard lump in the left groin may be caused by enlarged inguinal lymph nodes. Enlarged lymph nodes in the groin can cause swelling, pain and hardness in the groin. Hard lymph node enlargement is mostly due to malignant lesions, so you should improve the examination, clear diagnosis and then treatment. 3. Inguinal hernia: abdominal inflammation leads to increased abdominal pressure, the intestinal canal can pass through the inguinal canal opening into the groin, inguinal hernia, hernia sac contents are generally soft, hard, mostly due to incarceration, and should be treated in a timely manner. It is recommended that patients with a hard left groin should go to the regular hospital in time to find out the cause of the disease, under the guidance of professional doctors to take targeted treatment.