Small dots on the arms are considered to be related to urticaria, keratosis pilaris, eczema, vitiligo and other factors. 1. Urticaria: The occurrence of urticaria is considered to be related to factors such as life history, changes in the living environment, and medical history. For example, contact with, inhalation of, or ingestion of allergens may result in erythematous, bullous, and papular changes of the skin, accompanied by itching sensations. 2. Keratosis pilaris: Keratosis pilaris is also called perifollicular keratosis, the cause of which is still unclear, and it is considered to be related to the abnormality of the keratinization process caused by the gene mutation, and the lesions in the early stage are small pimple-like changes, accompanied by roughness, keratosis pilaris, thickening, dryness and desquamation. 3. Eczema: Eczema is an inflammation of the superficial dermis and epidermis caused by a variety of internal and external factors, which can occur in any part of the body. If it occurs in the arm, it leads to localized pimples and papules of the size of a pinhead to a grain of corn. In severe cases, small blisters can appear, and then fused with each other. 4. Vitiligo: Vitiligo is a primary, limited, generalized skin pigmentation disorder. The cause of the disease is not yet completely clear, the skin damage is skin hypopigmentation, whitening, resulting in local white dots. In addition to this, insect bite dermatitis, viral rash, drug rash, hemangioma, etc., can also lead to the appearance of small dots on the arm. It is recommended that the patient promptly to the hospital, after the cause of the disease is clear, under the guidance of the doctor standardized treatment, do not blindly use drugs.