Hard lumps at the root of a man’s thigh by his underwear are mainly caused by diseases, and common causes include ringworm, inguinal hernia, lipoma and so on. 1. Ringworm: ringworm is a skin disease infected by microorganisms, and the common causative organism is Trichophyton rubrum. Ringworm first grows on one side and then both sides can appear. Fungal infection will lead to the appearance of ring-shaped or semi-ring-shaped erythema in the groin and other parts of the patient, and the surface of the erythema will have pimples and scales. 2. Inguinal hernia: Inguinal hernia is an extra-abdominal hernia that occurs in the inguinal region, which is a mass formed by the protrusion of an abdominal organ through a weak defect. Typical symptoms of the patient are the appearance of a reproducible mass in the inguinal area, and when incarcerated, the mass will harden and increase in size and be accompanied by obvious pain. 3. Lipoma: Lipoma is a common soft tissue benign tumor, mainly composed of mature fat cells. Lipoma can be found in various parts of the body, and often appear as one or more lumps, which can be slightly pushed by fingers. When patients experience discomfort, they need to go to the hospital immediately.