White patches on the arms may be caused by vitiligo, florid chaff rash, anemia nevus and other diseases. 1. Vitiligo: Vitiligo is a disease caused by the destruction of melanocytes, the cause of which is not yet clear, and may be related to heredity, immunity, neurochemicals, etc. Patients will have white patches of skin, which can appear in any part of the body, especially the exposed parts. 2. maculopapular furuncle: maculopapular furuncle is caused by Malassezia violating the cuticle of the skin, patients will appear in the pore-centered maculopapular rash, the color of brown, light brown, white and so on, preferably in the neck, chest, upper limbs and other places. 3. Anemic nevus: Anemic nevus is mainly caused by abnormal development of vascular tissues, and patients will have single or multiple clear boundaries of pale white spots, preferably occurring on the trunk, but the face and limbs can also appear. There are many reasons for white spots on the arms, so it is recommended to consult a doctor for a clear diagnosis.