Psoriasis is a noncontagious skin condition that produces red, dry plaques of thickened skin. The dry flakes and skin scales are thought to result from the rapid proliferation of skin cells that is triggered by abnormal infection fighting cells (lymphocytes) from the blood . Psoriasis commonly affects the skin of the elbows, knees, and scalp. It gets better and worse spontaneously and may have periodic remissions (clear skin). Psoriasis can be controlled with medication.