Small blisters on the arms with itching may be caused by chickenpox, sweat herpes, eczema, etc. Further differential diagnosis by a doctor is required. 1. Chickenpox: caused by varicella zoster virus infection, can be manifested as herpes on the arm, accompanied by itching symptoms. 2. Sweat herpes: often manifested as a cluster of blisters on the skin, accompanied by pain and itching of the affected skin. 3. Eczema: often first appear skin erythema, on the basis of which can appear papules or herpes, and in severe cases can appear small blisters. It is recommended that the arm with small blisters with itching symptoms in a timely manner to the regular hospital, a clear cause, under the guidance of the doctor for standardized treatment, so as to avoid delays in the condition of the body to bring about adverse effects.