What Causes Psoriasis?

The cause of psoriasis is not fully understood. Recent research indicates that it is likely a disorder of the immune system in which the excessive reproduction of skin cells is secondary to factors produced by the immune system.

Scientists now think that, in psoriasis, an abnormal immune system causes activity by T cells in the skin. Normally, T cells help protect the body against infection and disease, but in the case of psoriasis, they mistakenly attack skin cells instead. The body then produces other immune system responses, leading to swelling and rapid production of skin cells.

In areas affected by psoriasis, there seems to be a rapid increase in the speed at which skin cells are replaced. Skin usually takes about 28 days to mature and shed, but in areas affected by psoriasis it only takes three or four days. The dead cells build up on the skin, forming thick, flaky patches called plaques.

It is not known what initiates the activation of the T cells.

Several factors are thought to aggravate psoriasis:

• Infections
• Diseases that weaken the immune system
• Stress
• Certain medications
• Smoking
• Certain chemicals
• Severe sunburn