A purple arm is caused by subcutaneous as well as muscular bleeding. The first thing you need to do is to go to the hospital for an emergency examination, and you can take a film to find out if there is a fracture in the upper arm. If a fracture has occurred, prompt hospitalization is required, and external fixation or a cast or surgery may be considered. If there is no fracture, but only soft tissue injury, symptomatic treatment is needed. A cold compress can be applied to the outside of the skin for a short period of time, using ice or cold towels, in order to cool down and reduce bleeding and leakage of surrounding tissue fluid. If the pain is obvious, you can take oral pain medication, such as Celecoxib, and after two days, you can apply hot compresses locally to accelerate the blood circulation around the area and dissipate the local bruises.