Small red dots on the arm without pain or itching may be caused by allergic purpura, vascular nevus, perikeratosis, etc., which can be treated by oral medication as well as by applying medication. 1. Anaphylactic purpura: The cause of anaphylactic purpura has not been fully determined, and may be related to contact with sensitizers, leading to inflammation and increased permeability of small blood vessels, causing small red spots on the arm to appear painlessly. It can be accompanied by arthralgia, abdominal pain and so on. The causative agent should be removed, and symptomatic supportive treatment can be oral antihistamine medication, such as loratadine tablets, cetirizine hydrochloride tablets and so on. 2. Vascular nevus: Vascular nevus is related to the expansion or proliferation of capillaries on the skin, which is manifested as small red spots on the arm without pain or itching. Avoid scratching, no effect on health, can be treated by laser. 3. Keratosis Pilaris: Keratosis Pilaris is a kind of follicular keratosis skin disease, which may be related to chromosomal inheritance and vitamin A deficiency, and it will lead to small red dots on the arm which are painless and itchy, and there is obvious roughness when touching it with hands. It can be treated by applying vitamin A acid ointment and salicylic acid cream under the guidance of a doctor. Small red dots on the arm without pain and itching may also be hives, thrombocytopenic purpura and other diseases caused by the patient should go to the hospital to do a comprehensive examination, to determine the cause of the disease in a timely manner to cooperate with the doctor for treatment, do not blindly use drugs.