Psoriasis. Artwork comparing two sections through human skin: healthy skin (left) and skin affected by psoriasis (right). Psoriasis is the presence of scaly lesions on the skin, caused by an increase in the rate at which new skin cells are produced. Normal skin consists of an epidermal layer of dead skin cells (light grey) that arise from a thin layer of living epidermal cells (dark grey). Below these is the large connective tissue layer of the dermis that also contains blood vessels (bottom). In psoriasis, constant division pushes older cells upwards from the living epidermal layer to flatten and die, forming a thick layer of painful, flaky skin (top).