A lump of flesh on the arm may be caused by lipoma, epidermal cysts, common warts and other diseases. 1. Lipoma: it may be related to genetic factors, abnormal lipid metabolism, chronic inflammation and other factors. The main manifestation is one or more soft lumps growing under the skin, which can be seen in any part of the body with fatty tissue. 2. Epidermoid cysts: the etiology may be related to skin injury, embryonic ectopic and other factors. Patients will have a smooth-surfaced, dome-shaped elevated swelling under the skin, which can appear in any part of the body. 3. Common warts: mainly caused by human papilloma virus infection. The patient will appear local surface rough, solid pimples, can occur in any part of the body. The reason for the growth of a flesh lump on the arm is not unique, it is recommended that the patient go to the regular hospital for relevant examination to clarify the cause of the disease.