Small white spots on the arms may be caused by vitiligo, florid chaff rash, idiopathic pitting pigmentation disorder and other diseases. 1.Vitiligo:The specific cause of vitiligo is not clear, it is considered to be caused by the destruction of melanocytes. Patients will have symptoms such as white spots on the skin, so patients will have the performance of small white spots on the arms. 2. florid chaff rash:florid chaff rash is due to malassezia infection, the patient’s main symptom is white dotted rash, slight itching sensation. As a result, patients will have the phenomenon of small white spots on their arms. 3. Idiopathic pitting hyperpigmentation:The cause of idiopathic pitting hyperpigmentation is not yet clear, and it may be due to the gradual atrophy and reduction of melanocytes after skin aging. Patients will have small white spots, the damage boundary is clear, not fusion and other symptoms, so the patient will have a small white spots on the arm performance. Patients with symptoms of small white spots on the arm should go to the hospital in time to identify the cause of the disease and follow the doctor’s instructions for treatment.