An itchy red patch on the body when you scratch it with your hands may be caused by artificial urticaria, insect bite dermatitis, contact dermatitis and other causes. 1. Artificial urticaria: its typical symptom is the skin is mechanically stimulated by the appearance of red masses with itching, usually in the waistband, jockstrap and other places. 2. Insect bite dermatitis: If you are bitten by mosquitoes, due to the mosquito saliva into the body, can make the body appear abnormal autoimmunity, so that the body appears itchy symptoms, if you scratch with your hands will be red. 3. Contact dermatitis: if contact with allergenic substances such as plasters, can cause an allergic reaction, the phenomenon of localized itching, scratching with the hand will be red. It is recommended that the itchy body scratching with a red piece of the person in time to go to the hospital, clear causes, under the guidance of the doctor for standardized treatment.