Soreness in the left arm is usually caused by strain, cold and occupational disease. 1. strain: left arm soreness may be overworked. The affected muscles, tendons, ligaments, soft tissue strains and other causes; overwork is easy to aggravate the condition, rest will generally be relieved. 2. Cold: the left arm cold will form aseptic inflammatory lesions in the local area, which can cause swelling of the affected area, inflammatory metabolites will stimulate the peripheral nerves around the pain. 3. Occupational diseases: If there are occupational diseases in the arm area, such as tumor, cyst, lipoma, etc., the compression of peripheral nerves can also cause pain in the affected area. Left arm pain may also have other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or standardized treatment.