A hard lump in the shoulder is commonly caused by the following conditions: 1. Hyperplasia and hypertrophy of the soft tissues around the shoulder joint, often due to chronic strain or acute injury to the shoulder joint, causing damage to the soft tissues, tendons, ligaments, and joint capsule around the shoulder joint, resulting in an inflammatory response, causing soft tissue hyperplasia and hypertrophy, resulting in a hard lump that can be felt under the skin. 2. Degeneration of the bones of the shoulder joint, which can also lead to osteophytes, and a hard lump can be felt under the skin. 3. Tumors in the soft tissue or bone tissue of the shoulder joint can cause swelling, which can be felt as a hard mass under the skin. In this case, you can brake and rest, and observe whether the hard mass is painful or not, and at the same time, physiotherapy, hot compresses, baking electricity and other physical treatments can be applied locally. If it is a soft tissue hyperplasia or hypertrophy, the hard mass will become soft or even smaller after treatment. If the pain is more serious, you need to go to the hospital.