Psoriasis is a chronic inflammatory skin condition that occurs when skin cells grow too quickly. People with psoriasis suffer from red, thickened areas of skin with silvery scales. This persistent skin condition is found most often on the scalp, elbows, knees, lower back and buttocks, but can cover larger areas of the body in severe cases. Psoriasis also can affect the nails and the joints with arthritis. Treatments include traditional topical medications, phototherapy, methotrexate, and biologic treatment.