Very itchy arms with a bump after scratching can be caused by a variety of reasons, such as contact dermatitis, eczema, and urticaria. At this time, patients need to avoid continuing to scratch to avoid aggravation of itching symptoms and even the appearance of skin lesions. It is recommended that patients go to the dermatology department of the hospital in time for examination and treatment after clarifying the cause. The common causes and treatment methods are as follows: 1. Contact dermatitis: It is an acute inflammatory reaction of the skin caused by skin contact with certain external substances, such as cosmetics, perfumes, etc. The contact area is itchy and may appear as a papule after scratching, manifesting as a grain of bumps, which can spread to the whole body in severe cases. Patients are advised to immediately get away from allergens, topical glycolic lotion can be used, and when symptoms are severe, oral benadryl can be prescribed to relieve itching; 2. Eczema: eczema is found on the forearms, calves, hands and feet, etc. Itching can occur on the arms, and a grain of bumps can appear after scratching. Patients can use topical glucocorticoids and calcium-regulated neurophosphatase inhibitors, such as trimethoprim ointment, dextran ointment, tacrolimus ointment, etc., and can also take oral loratadine, cetirizine and other drugs as prescribed by the doctor; 3, urticaria: arms are very itchy, scratching after a grain of bumps, common in artificial urticaria, bumps can be red, round, oval, etc., can be isolated or expanded into pieces, the skin surface The skin surface is uneven. Antihistamines, such as loratadine, epalrestine, and cetirizine, are preferred for treatment, and the itching symptoms as well as the skin bumps usually disappear within a few hours without leaving a trace.