A hard lump under the skin of the arm may be a sebaceous cyst, lipoma, subcutaneous nodule, enlarged lymph nodes, etc., and you should consult a doctor in time to find out the cause.
1. Sebaceous cysts: after the blockage of subcutaneous glands, the secretion tissue in the skin may not be discharged normally, and stasis and aggregation may be formed under the skin, resulting in the symptom of sebaceous cysts, which forms a large hard lump and usually does not have obvious pain.
2. Lipoma: It belongs to a kind of common soft tissue benign tumor, caused by the abnormal proliferation of fat under the skin, may grow in the superficial area or deep tissue, consists of single or multiple confined lumps, looks like a hard lump from the outside.
3. Subcutaneous nodules: Subcutaneous nodules are usually caused by long-term inflammation and infection of the skin, such as acne, pimples, scabies, etc., which cause certain trauma to the skin, resulting in the occurrence of hard nodules and hard lumps under the skin, which looks like a hard lump from the outside.
4. Swollen lymph nodes: Most of the swollen lymph nodes are caused by bacterial or viral infections, which will cause local lymphatic swelling and pain, resulting in the appearance of hard lumps under the skin of the arm.
If you have any of the above symptoms, you should consult your doctor to find out the cause of the problem and undergo the appropriate tests if necessary.