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Skin is made up of two layers: Upper layer called epidermis and lower or inner layer called dermis. In healthy individuals epidermal cells on skin are continuously shed off and replaced by new layer of cells. The cells of the lower most layer of epidermis called keratinocytes gradually mature as soft mature cells as they rise from lower layer to upper layer to become the most superficial layer of cells. This process takes around 28 days and it is slow insidious and almost inconspicuous as dead cells are efficiently cleared off and no debris is seen.

In Psoriasis regeneration of cells of epidermal layer is abnormally accelerated. It takes only 5–6 days instead of 28days for the keratinocytes to travel the distance from lowermost layer to become the uppermost layer. In the bargain these cells do not mature in such a short time and remain immature hard and scaly. Before the superficial layer is shed off & cleared new layer of immature & ill–formed cells is laid, this results in piling up of scales and thickening of skin.

Moreover in order to maintain such an increased production of cells, demand for blood & other constituents for cell manufacture at that site is markedly increased. The blood circulation to that area is increased manifold leading to congestion, redness(Inflamation)of skin. Thus a psoritic patch is formed.

Contributed by Dr. R. S. Sonawane