Psoriasis is a chronic disease that is caused by having an overactive immune system and the result of the skin production process moving too quickly. This sped-up process results in inflamed, itchy skin that may be red or scaly in appearance. Psoriasis appears in patches in areas of the skin that are already more difficult to keep moisturized such as your elbows, knees, and scalp. These patches of inflamed, dry skin can last for days or weeks at a time.