1, sitting posture is incorrect. Shrugging your shoulders, tilting your shoulders or looking down at your mobile phone for a long time will cause muscle tension in your shoulders, which will make your shoulders look fatter.

2. Improper exercise. Exercising your arms often without exercising your shoulders will lead to the relaxation of shoulder muscles and make your shoulders look fatter.

3. Genetic factors. Everyone's growth and development are different, and the proportion of different parts of the body is also different. So thin arms and fat shoulders are caused by genetic factors.