White dots on the arms may be physiological causes such as senile white spots, or pathological causes such as vitiligo, post-inflammatory hypopigmentation, lichen planus and so on. 1. Physiological reasons Age-related white spots: white spots on the arms may be age-related white spots, mainly caused by the decline of melanocyte function in the skin, is a kind of senile degeneration phenomenon, which is a normal physiological phenomenon, generally without treatment. 2. Pathological causes (1) Vitiligo: arm long white dots may be vitiligo, the cause is not clear, may be related to genetic, neuropsychiatric factors, autoimmune diseases, etc., can be manifested as a clear boundary of the skin surface of the milky white patches, the surface is smooth and without scales, generally no self-conscious symptoms. (2) post-inflammatory hypopigmentation: white dots on the arm may also be post-inflammatory hypopigmentation, if the arm has been traumatized or erythema, etc., in the improvement of the disease, the local area will be hypopigmented, and there may be white dots on the arm. (3) lichen planus: long white dots on the arm may also be lichen planus, generally caused by fungal infection of the skin, there may be white spots on the arm performance. There are many reasons for white dots on the arm, it is recommended to go to the hospital in time, under the guidance of the doctor for active treatment.