There are many reasons for itchy arms, such as allergic diseases, infectious diseases, chronic diseases of the body, physical causes of irritation and so on. 1. Allergic diseases: such as hives, contact dermatitis, drug rash, insect bite dermatitis and other allergic diseases, as well as eczema may lead to arm itching. 2. Infectious diseases: fungal infections caused by ringworm, Malassezia folliculitis, as well as viral infections caused by the early symptoms of herpes, may lead to arm itching. 3. Chronic diseases of the body: such as diabetes, liver disease, tumors and other diseases, may also cause symptoms of arm itching. 4. Physical causes of irritation: prickly heat caused by high temperatures; frostbite caused by low-temperature environments may also lead to itchy arms. Itchy arms, there may be other reasons, need to go to the hospital in time to check, follow the doctor’s instructions for treatment.