Psoriasis is a life-long chronic autoimmune disease characterized by thick scaly skin lesions and often associated with severe arthritis. In psoriasis, lesions skin cells, keratinocytes, grow too quickly, resulting in thick, white, silvery or red patches on skin. Normal skin cells grow gradually and flake off about every four weeks, but psoriasis causes new skin cells to move rapidly to the surface of the skin in days rather than weeks. Psoriasis symptoms often appear on the elbows, scalp, feet, knees, hands, or lower back, or as flaking or patches on the skin. It is most common in adults, but teenagers and children can also suffer from psoriasis.