Psoriasis is a skin disorder that causes skin cells to multiply up to 10 times faster than normal. This makes the skin build up into bumpy red patches covered with white scales. They can grow anywhere, but mostly appear on the scalp, elbows, knees, and lower back. Psoriasis is not contagious but can can be passed down genetically.
Psoriasis usually appears in early adulthood. For most people, it affects just a few areas. In severe cases, psoriasis can cover large parts of the body. The patches can heal and then come back throughout a person's life.