I have a red mark on my arm its been there 3 days an itches i try not to scratch but its still there?

Itchy skin area: Itchy skin lesions can be caused by an infection, dermatitis or eczema, solar injury, psoriasis, allergic reaction and many other skin disorders. A trial of over-the-counter medication like Cortaid (hydrocortisone) and lotrimin can actually help in treatment and in diagnosis. If the area does mot clear within few days, see your pcp or dermatologist.