Red, itchy, hairless skin on dogs is usually caused by parasitic infection, fungal infection, or allergic dermatitis. You need to check whether there are parasites on your dog. If there are parasites, perform external deworming in time; then use Use iodine to clean and disinfect the affected area, and then apply anti-fungal medicine; if it is allergic dermatitis, you need to use anti-inflammatory and anti-allergic medicine for treatment.