Hello, I understand your concern for itchy arms from sun exposure. It appears from your query that you have got polymorphous light eruptions due to exposure to sunlight on higher side. Whenever the sunlight is evident on skin on higher side it causes raised bumps with itching and redness on the affected area. In my patients with your kind of condition I suggest them to apply a mild steroid lotion such as fluticasone or mometasone for few days of period. For maintenance therapy if I were your treating doctor then would have prescribed you calamine lotion containing moisturizing factors to be applied at night time. For itching I suggest my patients to take an antihistamine such as cetrizine or levocetrizine for two times a day. Wear full sleeves clothes tot prevent the sun exposure and therefore I also suggest you to reduce the sun exposure on higher side. All the best.