A hard lump on the wrist may be caused by tendon sheath cysts, lipomas and dermatofibromas. 1. Tendon sheath cysts: the cause of the formation of this disease is not yet clear, may be related to the adjacent tissue degeneration, injury to long-term stimulation and other factors, mainly manifested as a hemispherical bulge under the skin, commonly found in the wrists, ankles and other joints. 2. Lipoma: Lipoma disease is still unclear, the disease is mostly seen in the trunk, limbs and other places, there will be localized lumps under the skin. 3. dermatofibroma: dermatofibroma is not clear, the clinical manifestations of the outer limbs and other places appear firm nodules. Causes of wrist long a hard lump of more reasons, patients are recommended to consult a doctor for examination, clear cause.