Small blisters on the arm, feel itchy consider may be herpes zoster or chickenpox, as follows: 1. Herpes zoster: usually occurs unilaterally on the upper limbs, can be accompanied by a certain amount of pain, blisters are distributed in clusters, due to varicella-zoster virus infection, mainly occurs in the elderly or children with low immunity, can be secondary to hypertension, hyperlipidemia, diabetes and other serious medical diseases. Patients can take oral vaxilovir hydrochloride granules, famciclovir tablets, mecobalamin capsules, topical acyclovir ointment or ganciclovir ointment, inotropic drugs such as adenosine cobalamin injection, etc.; 2. Chickenpox: In addition to small blisters on the arms, such rashes can occur in other parts of the body, including oral mucosal fluids. Patients can take acyclovir tablets orally and apply glyburide lotion for treatment.