If you have a hard lump the size of a green bean under your skin, you should consider sebaceous cysts, nodular itchy rash or sclerofibromatosis. 1. Sebaceous cysts: When the excretory ducts of sebaceous glands are blocked, their contents gradually increase, and the sebaceous cystic epithelium swells, causing retention cysts, which contain tofu dregs-like secretions, are movable, moderately hard, and have a smooth surface. 2. Nodular itchy rash: it can be related to emotional state or insect bites and other reasons, at first it is a pin cap to rice grain-sized papule, gradually increasing to become mung bean to soybean-sized, hemispherical, firm and elevated skin surface papules and nodules, with obvious keratinization at the tip and wart-like appearance, brown or gray-brown in color, which often causes intense itching. 3. Sclerofibroma: the specific etiology of this disease is not clear, it is generally believed that heredity, surgery, trauma and other reasons can cause the disease occurs, the appearance of localized hard lumps, no pressure and pain sensation, can occur in various places. Subcutaneous hard lumps may also be caused by other reasons, need to consult a doctor in a timely manner, to clarify the nature of its treatment in accordance with medical advice.