Big bumps on the arm is very itchy, mostly considered to be local skin allergies triggered by contact dermatitis, should be used hydrocortisone butyrate cream and other glucocorticoid anti-allergy treatment, but also can not be ruled out is the papular urticaria, should be orally loratadine and other antihistamine medication. 1. Contact dermatitis: when the skin contact with exogenous substances produce stimulation, can cause allergic reaction, can be manifested as erythema, edema, accompanied by itching. Treatment of the acute stage can be used glycerite lotion cleaning. In the subacute stage with oozing, glucocorticoids such as hydrocortisone butyrate cream can be used to apply, and antihistamines such as loratadine can be taken orally for treatment. 2. papular urticaria: insect bites are a common cause of papular urticaria. At the onset of the onset of different sizes, fusiform, accompanied by obvious itching. If the affected area of the skin is swollen, itching is obvious, you can do cold wet compresses, mild rashes can be used externally glycerine lotion to relieve itching, with oral cetirizine, loratadine and other antihistamine treatment. The use of the above drugs need to follow the doctor’s instructions. Itchy pimples on the arm may also be caused by other reasons, it is recommended that the patient to the hospital in time, clear cause of the disease under the guidance of the doctor standardized treatment.