Subcutaneous hard nodules may be caused by fibromas, sebaceous cysts, and enlarged lymph nodes. 1. Fibroma: usually found unintentionally, painless or slightly painful hard subcutaneous nodules appear on the limbs or trunk. 2. Sebaceous cysts: If the sebaceous gland secretions are blocked under the skin, cysts may form and appear as hard subcutaneous nodules. 3. Enlarged lymph nodes: Lymphadenitis or lymphoma can lead to enlarged lymph nodes, which may appear as hard nodules under the skin. It is recommended that people with subcutaneous nodules should go to the hospital in time to clarify the cause, and if treatment is needed, standardized treatment should be carried out under the guidance of the doctor, so as to avoid the delay of the disease and bring adverse effects to the body.