Hard lumps in the flesh of the inner side of the upper arm may be lipomas, subcutaneous nodules, swollen lymph nodes, etc. The cause needs to be identified and treated promptly. 1. Lipoma: it is a common benign tumor, which can appear in any part of the body. It is caused by abnormal proliferation and accumulation of adipose tissue, and the tumor can persist and gradually increase in size, which can be removed by surgery. 2. Subcutaneous nodules: hard lumps in the flesh of the inner side of the upper arm may also be subcutaneous nodules, which may be caused by infection, allergic reaction, foreign body stimulation, endocrine or metabolic disorders, skin tumors and other diseases. It is necessary to identify the specific cause of the disease in a timely manner. 3. Enlarged lymph nodes: under normal circumstances, the lymph nodes on the inner side of the human arm can not be touched, when the lymph nodes are enlarged, they can also be manifested as hard lumps inside the flesh of the inner side of the arm, which can lead to the enlargement of the lymph nodes of a number of etiological factors, such as inflammation, metastasis of malignant tumors, and so on, it is necessary to identify the causes of the disease in time, and intervene in the treatment as soon as possible under the guidance of a professional physician, which can improve the prognosis. When there are hard lumps in the flesh of the inner side of the upper arm, it is recommended to consult a doctor in time to clarify the cause.