Psoriasis - Causes

Helper-T cells and Cytokines. TH cells also secrete or stimulate the production of powerful immune factors called cytokines. In small amounts, cytokines are indispensable for healing. If overproduced, however, they can cause serious damage, including inflammation and injury during the psoriasis disease process. In psoriasis, researchers are particularly interested in cytokines known as GRO-alpha, tumor necrosis factor, and certain interleukins.

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Neutrophils. Cytokines attract to the scene large numbers of other large white blood cells known as neutrophils. Neutrophils stimulate the production of arachidonic acid, which triggers about 30 different chemicals, including two key players in the inflammatory process:

Leukotrienes, which attract even more white blood cells to the area.
Prostaglandins, which open blood vessels and increase blood flow.

Genetic Factors

A combination of genes is involved with increasing a person's susceptibility to the conditions leading to psoriasis.

HLA Molecules. The processes leading to all autoimmune diseases involve the human leukocyte antigen (HLA) system, which is genetically regulated. HLA molecules are designed to pick off parts of antigens and present them on the surface of a cell so that the various infection-fighting factors in the immune system can recognize and destroy them. Malfunction of this system is at the root of most immune disorders, including psoriatic arthritis. For example, psoriasis patients with a specific HLA genetic factor called HLA-CW6 tend to develop psoriasis at an earlier than average age. However, only 10% of people who harbor these genes develop psoriasis. Other genetic and environmental factors, then, are required to actually trigger the disease.

PSORs. Researchers have now identified four key genes (named PSORs 1-4) that are involved with psoriasis. Of particular interest are the genes located in regions on specific chromosomes that are linked to HLA and tumor necrosis factor, an immune component strongly associated with psoriasis.

Environmental and Other Triggers

Outside factors, including weather, stress, injury, and infection, while not direct causes, are often important in triggering the disease process leading to onset and worsening of psoriasis.

Weather. Weather is a strong factor in psoriasis:

Cold, dry weather is a common precipitant of psoriasis flare-ups.
Hot, damp, sunny weather helps relieve the problem in most patients.
To confuse matters, some people have photosensitive psoriasis, which actually improves in winter and worsens in summer when skin is exposed to sunlight.