Common rashes that cause legs to itch are stasis dermatitis, atopic dermatitis, psoriasis and lichen planus. These rashes can also appear on different parts of the body. Atopic dermatitis is a common rash that can appear as a patch on the legs, trunk and neck of people and causes inflamed skin, relates the Mayo Clinic.
Stasis dermatitis is a condition that occurs due to poor circulation. It causes a rash that is itchy and can ooze fluid, reports MedicineNet. Lichen planus is another condition that also causes an itchy rash that can manifest on the legs, genitals, wrists or mouth. Other symptoms associated with lichen planus are blisters and scratch marks, reports the National Institute of Health. A rash like psoriasis can appear on people's knees.