A lot of small pimples on the arms may be due to eczema, urticaria or keratosis pilaris, the patient can be under the guidance of the doctor to clarify the cause of the disease through oral medication or topical medication to carry out the treatment. 1. Eczema: Eczema is usually caused by skin allergies, lesions manifested in a variety of forms, can be manifested as many small pimples in the arm area, accompanied by itching. In the treatment, patients can use topical hormonal drugs, such as dinexed cream, hydrocortisone butyrate cream and so on. 2. Urticaria: The lesions of urticaria appear as different sizes of wind bumps, accompanied by intense itching. In the treatment, you can use topical glycerite lotion, or oral antihistamine such as levocetirizine hydrochloride to desensitize and relieve itching. 3. Keratosis pilaris: Keratosis pilaris is generally associated with genetic factors, commonly known as chicken skin, manifested as follicular keratinization of the arms on both sides of the protruding follicles, can be used externally with retinoic acid cream to carry out the antikeratinization treatment. Arm a lot of small pimples may also have other reasons, such as folliculitis, dermatitis, flat warts, etc., it is recommended to go to the regular hospital in a timely manner, under the guidance of a professional doctor for targeted treatment.