Small particles on the arm that don’t itch may be keratosis pilaris, infectious molluscum contagiosum, flat warts, etc., and you should consult a doctor in time to find out the cause. 1. Keratosis Pilaris: Keratosis Pilaris is usually associated with heredity and is caused by excessive keratinization of the hair follicles. The skin surface touch follicles can be seen raised small particles painless, like goose bumps. 2. Molluscum contagiosum: Molluscum contagiosum is a skin disease caused by molluscum contagiosum virus infection, the surface of the infected skin will appear the size of rice grains of dermatological pimples, the surface of the umbilicus can be seen. The molluscum contagiosum is not a symptom of the disease, but it may cause a lot of small bumps on the arms, which are painless and itchy. 3. flat warts: a viral skin disease caused by human papillomavirus infection, usually can occur in any part of the human skin, but also can occur in the arm, manifested as a skin-colored or brown flat papules, the surface is smooth, usually painless and itchy. This symptom alone is not enough to diagnose the disease, there may be other factors that cause it. It is recommended that the patient consult a doctor in time to clarify the cause of the disease and give targeted treatment.