Itchy bumps on the arms may be caused by eczema, insect bite dermatitis and other factors, the patient should consult a doctor in a timely manner to clarify the cause of the disease. 1. Eczema: small bumps on the arm and itchy may be caused by eczema, the onset of a variety of internal and external factors, such as endocrine and metabolic changes, neuropsychiatric factors, genetic factors, food, inhalants, living environment. Patients will appear on the arm of the red spots, papules, blisters and other polymorphic skin lesions, accompanied by significant itching. 2. Insect bite dermatitis: small bumps on the arm and itchy may be caused by insect bite dermatitis, belonging to the bite of local skin allergies and inflammatory reactions. Localized edematous pemphigoid-like papules, papules or petechiae may appear, accompanied by obvious itching. Itchy bumps on the arm may also be caused by other diseases, specific need to go to the hospital to clarify the cause of the disease.