In the past decade, there have been many advances in our understanding of how psoriasis might develop and how it can be treated. The question remains: Why does it occur?
Psoriasis is a complex disease that is caused by several factors. Although there is no known single cause for psoriasis, it is clear that genetics, the skin cells (keratinocytes), environmental factors, and the immune system play central roles in causing this disease. Psoriasis has a strong genetic component, and there are multiple genes that likely need environmental triggers to activate psoriasis. There are many theories as to why psoriasis occurs in susceptible people, but no one has been able to pinpoint the exact cause. We now understand, however, that there are several key steps in the process, and that the immune system plays a critical role.
Traditionally, a leading theory proposed that psoriasis was caused by an abnormality in the outer layer of the skin (epidermis), and that the unrestricted growth of the epidermis led to an increased growth rate of these cells - in psoriasis the skin cells grow more rapidly, often during three to five days (as opposed to the normal twenty-eight-day cycle); they divide much faster than normal skin cells, and the number of cells multiplying is doubled, which, in turn, leads to thickening and scaling skin. In other words, it was believed that somehow the skin of people with psoriasis was different and, therefore, led to the disease.
While these understandings are important, increasing attention has focused on the immune system as pivotal in the development of psoriasis. Specifically, the red, thick, and scaly changes seen in the skin occur in reaction to a faulty signal from the immune system to the skin. In other words, the inflamed plaques of psoriasis arise from a series of abnormal reactions in the skin.
The Immune System
The immune system is the first line of defense that guards our body from foreign substances. In the last two decades, compelling scientific information has suggested that the immune system is the most important factor in causing psoriasis. One important observation that was helpful in developing this concept came about when a chance clinical observation revealed an improvement in psoriasis symptoms in patients being treated with cyclosporine for their arthritis. Although cyclosporine was not being used for the patient's psoriasis, the unexpected improvement helped open the door to using cyclosporine for psoriasis and, in part, to new understandings about the causes of psoriasis.
Cyclosporine is a drug used to prevent the rejection of transplanted organs. It acts by suppressing the immune system, an effect that led to improvements in psoriasis. Thus, a link between the immune system and psoriasis was made. This discovery was one of the first indications that psoriasis was caused, in part, by imbalances in the immune system. Since that observation was made, scientists have been accumulating evidence that established that the immune system plays a central role in the development of psoriasis, partially by sending a faulty signal to the outer layer of the skin (epidermis), which causes it to thicken.
The significance of these discoveries cannot be overstated. They led to a clearer understanding of the exact way psoriasis occurs, thereby providing scientists with the opportunity to develop new medications that can specifically target the immune system and ultimately allow us to use new medicines to effectively treat this capricious disease.
The Immune System and Disease
When our immune system functions normally it is able to effectively protect us against invading microorganisms, such as bacteria, viruses, and fungi, and foreign substances called antigens, as well as to prevent the occurrence of cancer and other diseases. The importance of an intact, functioning immune system can be readily appreciated when we visualize what happens if this system is disturbed. For example, individuals with inherited abnormalities of the immune system are prone to frequent infections and cancers.
In addition, the immune system is able to survey the skin and other organs, detect precancerous and cancerous changes, and possibly prevent the development of certain cancers. People with acquired immune deficiencies, such as acquired immune deficiency syndrome (AIDS), are prone to serious infections and cancers.
While a decrease in our immune system can make us susceptible to diseases, an increase or overstimulation of our immune system can lead to a type of disease called autoimmune disease. An autoimmune disease is caused, in part, by an overstimulation of our body's immune defenses, in which our immune cells start attacking our healthy cells. This happens in part because our immune cells fail to recognize our healthy cells, mistaking them for a foreign substance and attacking them. To find out more, you can check out What Causes Psoriasis.