By definition, psoriasis is a condition that causes red, flaky, and crusty patches of skin that is covered with silvery scales. These tend to present on your elbows, knees, scalp, and lower back. However, they may appear anywhere on your body. Psoriasis is a lifelong condition, but there may be periods when symptoms are mild or not present. On the other hand, there may also be periods of severe symptoms. Learn more about the condition and the types of psoriasis diagnosis tests used.