Arm skin is easy to allergy, may be because the patient himself belongs to the allergic body, coupled with the arm skin belongs to the more exposed parts of the body, easy to contact with pollen dust, easy to be mosquito bites, so it will cause allergic reactions. 1. Allergy: patients belong to the allergic body, in the intake of food (eggs, mango), drugs (penicillin, sulfonamide), contact with pollen, animal fur, etc. easily triggered by allergic reactions, so that local or generalized skin allergies. 2. Arm skin belongs to the exposed parts: face and neck, chest and arm are exposed parts, easy to contact with external factors stimulation, higher than other parts of the allergic reaction. Arm skin allergy causes more, it is recommended to go to the hospital for allergen examination, under the guidance of the doctor for targeted treatment.