Hard lumps under the skin may be caused by sebaceous cysts, fibromas, enlarged lymph nodes and other reasons. 1. Sebaceous cysts: If the secretion of the hair follicle can not be discharged normally from the mouth of the hair follicle, it can form a lump under the skin. Sebaceous cysts are usually soft, but can become hard when infected. 2. Fibroma: the onset of the disease is more insidious, the patient may inadvertently find that the limbs or trunk of the subcutaneous presence of painless or slightly painful swelling. 3. Enlarged lymph nodes: malignant diseases such as lymphoma, lymphoblastic leukemia, lymphatic metastasis of malignant tumors can lead to enlarged subcutaneous lymph nodes. These enlarged lymph nodes have hard texture, poor mobility and no tenderness. 4. Folliculitis: Inflammation of skin follicles due to bacterial infection is called folliculitis. Early palpation can find a hard lump under the skin, tenderness, skin redness and swelling. It is recommended that people with hard lumps under the skin go to a regular hospital in time to clarify the cause of the disease and carry out standardized treatment under the guidance of the doctor, so as not to delay the disease to bring adverse effects on the body.