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Why do I have this disease?

Although the exact cause of psoriasis is yet to be found, researchers believe a combination of genetic, environmental and immune factors may be involved.

In terms of genetics, there are many different psoriasis risk genes, and they all play a part in developing the condition. If someone in your family has psoriasis, you’re more likely to develop it. For instance, if one of your siblings has psoriasis, your risk for developing it is 4 to 6 times greater than that of the general public. About 40% of patients with psoriasis and psoriatic arthritis are estimated to have a family history.

Though there is a genetic component that elevates risks, many people with a family history of the disease will not go on to develop psoriasis.

Researchers believe that for a person to develop psoriasis, that person must have a combination of the genes that cause psoriasis and be exposed to specific external factors known as “triggers.” Psoriasis triggers vary–what may cause one person’s psoriasis to become active, may not affect another. Triggers can also change for an individual over the course of one’s condition. Common triggers include infections (e.g., strep throat), reaction to medications (e.g., antimalarials, beta-blockers, lithium) and injury (e.g., sunburns, scratches).

Within this context of genetic and environmental components, psoriasis is ultimately a disorder of the immune system.


How Does This Disease Develop?

In skin that is not affected by psoriasis, skin cells take about 28 days to regenerate.

With plaque psoriasis (see figure), the immune system becomes overactive and, as a result, skin cells turn over in 3-7 days, causing a build-up of skin (referred to as plaques). In people with lighter skin with psoriasis, plaques are typically pink-red and tend to have more overlying scale; in people of colour with psoriasis, lesions are more violaceous in colour (i.e., purplish, grayish). As a result, skin affected by psoriasis can be thick, painful and itchy.

At a basic level, this process perpetuates itself with white blood cells (called T-helper lymphocytes – or Th cells ) becoming overactive and producing excess amounts of cytokines (proteins important in cell signalling). In turn, these chemicals further trigger inflammation in the skin and other organs.

psoriasis perpetuation of inflammation

Click to enlarge

Overall, psoriasis is a dynamic disease involving the interplay between immune cells, keratinocytes and other skin cells. The inflammatory process and genetic risk factors seen in psoriasis may also be associated with other chronic inflammatory diseases including psoriatic arthritis. Thus, the risk of developing certain conditions is higher in people with psoriasis compared to the general population.

Cytokines are small proteins that control the growth and activity of other immune system cells and blood cells. When released, they signal to the immune system to do its job. Cytokines affect the growth of all blood cells and other cells that help the body's immune and inflammation responses.

The primary type of cell found in the epidermis, the outermost layer of the skin.

A type of T cell that play an important role in the immune system, particularly in the adaptive immune system. When stimulated by a specific antigen (foreign substance) they "help" the activity of other immune cells by releasing cytokines, small protein mediators that alter the behavior of target cells that in turn, express receptors for those cytokines. Subsets of Th cells (e.g., Th1, Th17) produce different cytokines.

A subsystem of the immune system that is made up of specialized, systemic cells which process and eliminate germs (e.g., bacteria and viruses) or prevent their growth. The adaptive immune system "remembers" germs, so the next time a known germ is encountered, it can respond faster (known as immunological memory). Antibodies are a critical part of the adaptive immune system. By specifically targeting the type of germ that is causing the infection, the adaptive immune system takes over if the innate immune system – the body’s first line of defence that doesn’t distinguish between different germs – is not able to destroy the germs. For this reason, the adaptive immune system is slower to respond than the innate immune system, but when it does, it is more accurate.