Red pimples that look like pimples on the arms may be related to folliculitis, contact dermatitis, periorbital keratosis and other causes. 1. Folliculitis: a local inflammatory reaction caused by purulent bacterial infections such as Staphylococcus aureus, which may appear as skin papules and manifest as red pimples like pimples. 2. Contact dermatitis: if the arm contact cream and other allergenic substances, can cause the body to abnormal immune response, can be manifested as red pimples. 3. Keratosis pilaris: due to genetic and other factors can cause follicular keratosis pilaris on the arm, can be manifested as red pimples. It is recommended that people with red pimples on the arm like acne go to the hospital in time to clarify the cause of the disease and standardize the treatment under the guidance of the doctor.