psoriasis how to tame the itch but not make the rash worse

Avoid perfumed or scented products. Any household products such as cleansers, detergents, and fabric softeners that are strongly scented can worsen your itchy skin. “It is a good idea to use those that are clearly marked ‘fragrance free’ or ‘hypoallergenic,’" suggests Robles.
Take short baths in tepid water. You may prefer long soaks in hot water when you take a bath or shower, but that’s a no-no if you want to prevent or stop the itch. This is because water — hot water, in particular — removes some of the natural moisturizers in the upper layers of your skin.

Use a mild body wash. To protect your skin from irritants, stay away from harsh soaps, and opt for milder ones or other hypoallergenic cleansers. Also, resist slathering on a lot of cleanser, since even mild ones can dry your skin — and the drier your skin, the more it itches.
Take a spa bath. Add some oatmeal, Epsom salts, or Dead Sea salts to your bath water. Just don’t soak for too long, and follow the recommendations on the package for bathing.
Pat your skin dry. Vigorously rubbing can irritate your skin, causing it to itch more, Robles says.

Apply moisturizer religiously. Think thick and greasy — these choices will stick to your skin more effectively than lotions. Apply them within a few minutes of drying off from your bath. That way, the cream will be able to trap moisture in your skin before it can evaporate. This may also be the best time to apply prescription creams and ointments. Ask your doctor if these medications can be applied to wet skin and be sure to apply them first, followed by the over-the-counter moisturizer.
Try antihistamines. Colby Evans, MD, a dermatologist in Austin, Texas, recommends "non-drowsy formulas in the morning and Benadryl at night.” If over-the-counter antihistamines don’t help you, talk to your doctor about prescribing stronger ones. Antihistamines work by targeting the nerve pathways that are related to itching.
Apply ice. Ice numbs your nerve endings, making it a quick, easy, and cheap way to relieve the pain and itching that psoriasis lesions can cause. Placing your regular moisturizer in the refrigerator can have a similar effect.