Is Psoriasis an Immune System Disorder?

Researchers believe the immune system sends faulty signals that speed up the growth cycle in skin cells. Certain people carry genes that make them more likely to develop psoriasis, but not everyone with these genes develops psoriasis. Instead, a "trigger" makes the psoriasis appear in those who have these genes. Also, some triggers may work together to cause an outbreak of psoriasis; this makes it difficult to identify individual factors.
Possible psoriasis triggers include: emotional stress; injury to the skin; some types of infection; reaction to certain drugs. Once the disease is triggered, the skin cells pile up on the surface of the body faster than normal. In people without psoriasis, skin cells mature and are shed about every 28 days. In psoriatic skin, the skin cells move rapidly up to the surface of the skin over three to six days. The body can't shed the skin cells fast enough and this process results in patches also called "lesions" forming on the skin's surface.