Psoriasis is a long-term (chronic) skin problem that causes skin cells to grow too quickly. This growth causes thick, white, silvery, or red patches of skin (called plaques).

Normally, skin cells grow gradually and flake off about every 4 weeks. New skin cells grow to replace the outer layers of the skin as they shed. But in psoriasis, new skin cells move quickly to the surface of the skin in days rather than weeks. They build up and form thick plaques. The plaques range in size from small to large. They most often appear on the knees, elbows, scalp, hands, feet, or lower back.

Psoriasis is most common in adults. But children and teens can get it too.