Small white spots on the arms may be vitiligo, florid furfura, post-inflammatory hypopigmentation, and so on. 1. Vitiligo: this is a pathogenesis is not clear, common acquired pigment loss skin mucosal disease, will involve the hair follicles, some patients with the condition of the early lesions are relatively small, there will be a small white spots, high incidence in the forearms extensor, the face, hands, neck and so on. 2. maculopapular furuncle: Malassezia violates the cuticle of the skin will cause superficial skin infection, the lesions show a variety of symptoms, such as light brown, brown, yellowish, white, etc., the lesions are round or round-like, will gradually increase, generally no self-conscious symptoms. 3. Post-inflammatory hypopigmentation: If there is a history of some skin diseases, such as eczema, dermatitis, etc., these diseases will appear in the local hypopigmentation after the recovery, causing small white spots, usually appearing in the lesions of the primary disease. Small white spots on the arm should be taken seriously, seek medical attention as soon as possible, identify the cause and then regular treatment, so as not to delay the condition.