Small red bumps on the arms are more likely to be considered as insect bite dermatitis, which is mainly due to an allergic reaction after an insect bite. The rash can appear as a pimple or pimple like rash with some itching. For treatment, you can take one capsule of levocetirizine hydrochloride orally one night a day, together with compound glycopyrrolate capsules 3 times/day, 2 capsules/time. For small red bumps, if the redness and swelling is more serious and obvious, and the skin temperature is higher and there is tenderness when pressed, it means that the inflammation is very serious, you can apply fusidic acid cream. After the rash darkens and the swelling subsides, apply a glucocorticoid ointment, such as hydrocortisone butyrate ointment, or a non-steroidal anti-inflammatory cream like butyl flufenamic acid ointment.