The causes of psoriasis are still unknown. The rapid skin growth and inflammation combine to cause the skin changes that lead to psoriasis. The process which triggers the skin growth and inflammation remains obscure, and active research is being carried out to identify these events.
Under the microscope, skin affected by psoriasis is thicker than normal skin, with dramatic thickening of the epidermis (hyperkeratinization) and inflammation caused by a type of white blood cell called T cells. These T cells react against parts of the skin where the disease is active. The T cells and other immune system cells make cytokines, immune-system chemicals such as tumor necrosis factor alpha) and IL23 (interleukin 23) that aid in their communication and activation.
Chronic inflammation in these areas causes skin cells to divide and turn over much more rapidly, up to four to five times as quickly as in normal skin. The rapid buildup of these skin cells, called keratinocytes, can lead to thick white scales on top of psoriatic skin.
Over time, new, small blood vessels support the actively developing psoriatic plaques and may a persistent reddening of affected skin even after treatment. It is not yet clear why the T cells become activated in the skin in psoriasis and other immune diseases. Once the process starts, it seems to persist for life. How to inactivate or “turn off” these particular T cells permanently without impairing the immune system as a whole or causing serious side effects is a significant treatment challenge for scientists and is the focus of active immunology research.
Some researchers have found found that the possible genes associated with psoriasis are part of the immune system. The HLA-C gene appears to be consistently important in the onset of psoriasis. The HLA is a group of genes on chromosome 6 that encodes sequences, or directions, for proteins on white blood cells. The white blood cells including the T cells, primed to defend against infection, are sometimes activated inappropriately in different parts of the body and areas of skin. These areas of skin respond with the skin thickening, redness and the scale of psoriasis.
Now that active research into the cause of psoriasis has uncovered the fact that certain immune system genes are associated with this and other immune process, the next step is to use this information to develop new psoriasis treatments.