Slide show: Common skin rashes

Psoriasis (suh-RIE-uh-sis) is the rapid buildup of rough, scaly skin that occurs when the life cycle of skin cells rapidly increases. The extra skin skin cells form thick, silvery scales and red patches that are itchy and sometimes painful.

The condition tends to flare up periodically and then subside for a time.

For some people, psoriasis is a mild nuisance. For others, it can be disabling, affecting extensive areas of skin for long periods and often occurring with a distinct type of arthritis (psoriatic arthritis). Topical medications and light therapy may help reduce signs and symptoms of the skin lesions.