The itchy bumps on the arms can be the following possibilities: eczema, psoriasis and scabies. 1. eczema: mainly caused by allergic diseases, the bumps can be accompanied by polymorphic lesions such as erythema, oozing and crusting, etc. In terms of treatment, you can take oral levocetirizine hydrochloride tablets, loratadine tablets, or olopatadine hydrochloride tablets, and if severe, you can take oral compound glycopyrrolate capsules. In addition, you can use topical mometasone furoate ointment or denide ointment. 2, psoriasis: white scales can be seen on the basis of small bumps, and punctate bleeding can be seen under the scraped scales, which means that the three phenomena of psoriasis are positive, and in treatment, you can take oral compound amineptine tablets and compound glycyrrhizin capsules, and use topical hydrocortisone butyrate ointment. 3, scabies: topical sulfur ointment is needed for treatment.