Itchy pityriasis. Pityriasis rosea last six weeks or less, and improves with ultraviolet light or topical steroids. Frequently and/or aggressively scratching pityriasis rosea can result in chronic eczema, that lasts indefinitely. Also, breakdown in the skin barrier increases risk of skin infection. Do your best to avoid scratching. Use moisturizing ointments or otc pramoxine. Cool compresses also decrease the itch.
Pityriasis. You may get a secondary fungus or bacterial infection. This disease is sometimes very itchy and the best thing to do is see a skin doctor to help this. It is not contagious.