There is a lump inside the right arm that hurts when pressed. Consider inflammation, trauma, tumors and other causes. 1. Inflammation: soft tissue infection will appear as a localized lump, local skin redness, swelling and heat, and obvious pressure pain. It can be clearly diagnosed by ultrasound. 2. Trauma: soft tissue injury or fracture and other reasons can also appear local lumps, through the film examination can be clearly diagnosed. 3. Tumor: benign tumors include lipoma, fibroma, chondroma and so on; malignant tumors include giant cell tumor of bone, osteosarcoma, metastatic tumor and so on. Through ultrasound or CT examination can be clear, need to perform surgical resection. There is a lump in the right arm that hurts when pressed, and you need to go to the hospital for further examination and treatment to clarify the cause of the disease.