The common causes of itchy back of the hand are: pruritus, contact dermatitis, insect bite dermatitis, eczema and so on. 1. Pruritus: it is a disease that only has skin itching without skin damage, which can be caused by dry skin on the back of the hand, internal medicine diseases or mental psychological factors, etc. So it can cause itching on the back of the hand. It can be caused by dry skin on the back of the hands, medical diseases or mental and psychological factors. You can follow the doctor’s instructions to apply glycerine lotion, etc. to relieve itching. 2. Contact dermatitis: If the back of the hands are exposed to laundry detergent, washing powder and other chemicals that are too alkaline, contact dermatitis can be caused, resulting in itching, pimples and erythema on the back of the hands. 3. Insect bite dermatitis: mosquitoes will inject toxins into the body along the skin after biting. If the back of the hand is bitten by mosquitoes, it can trigger an inflammatory reaction of the skin, followed by symptoms of itching. 4. Eczema: stimulated by a variety of factors inside and outside the body, mainly due to hand contact with certain allergic substances induced, can be manifested as a bilateral symmetrical distribution and border unclear rash, accompanied by itching. To summarize, if the back of the hand skin itchy, it is recommended to consult a doctor in a timely manner to clarify the cause of the disease and symptomatic treatment.