Psoriasis is an inflammatory skin condition characterized by red itchy patches of skin covered with silvery-white scales. It’s a chronic condition. Symptoms can come and go, and can range in severity.

Psoriasis is a common condition, affecting 2 to 3 percent of the world population. More than 7.5 million people in the United States have psoriasis.

The exact cause of psoriasis isn’t certain. It’s thought to be a combination of genetics, environmental factors, and your immune system.

Based on research developments in the past few years, psoriasis has generally been classified as an autoimmune disease. This means that your immune system cells, called T cells, mistakenly attack your own skin cells as foreign invaders. This causes your skin cells to rapidly multiply, leading to the characteristic psoriasis skin lesions.

Not all researchers think that psoriasis is an autoimmune disorder. Some agree that psoriasis is an immune-mediated condition. But their theory is that psoriasis results from gene-related abnormal reactions to skin bacteria.

Normally your immune system recognizes your own cells and doesn’t attack them. Autoimmune diseases are when your immune system mistakenly attacks healthy cells as though they were outside invaders attacking your body.

There are more than 100 autoimmune diseases. Some autoimmune diseases involve just one part of your body — such as your skin in psoriasis. Others are systemic, involving your whole body.

What all autoimmune disorders have in common is that they’re caused by a combination of genes and environmental factors.

Exactly how the genes and environmental factors interact to cause many different diseases is the topic of ongoing research.

So far, what’s known is that people with a genetic predisposition to autoimmunity may have 2 to 5 times the chance of developing an autoimmune disease as people who don’t have a genetic predisposition.

The group of genes involved is called the histocompatibility complex, known as HLA. HLA is different in every individual.

A genetic predisposition to autoimmunity may run in families, but family members may develop different autoimmune disorders. Also, if you have one autoimmune disorder, you have a higher risk of getting another one.

There’s less known about the specific environmental factors that trigger an autoimmune disease in someone who has a genetic predisposition to autoimmunity.

Common autoimmune conditions

Here are some of the more common autoimmune disorders:

The majority of scientists today believe psoriasis is an autoimmune disease. It’s long been known that the immune system is involved in psoriasis. But the exact mechanism isn’t certain.

In the past two decades, research has established that the genes and gene groups associated with psoriasis are shared with known autoimmune disorders. Research also established that immunosuppressant drugs are effective new treatments for psoriasis. These drugs work by suppressing the immune system that’s attacking healthy tissue.

Research is ongoing on the role of the immune system’s T cells in psoriasis. T cells are the immune system’s “soldiers” that normally combat infections. When the T cells misfire and instead attack healthy skin, they release special proteins called cytokines. These cause skin cells to multiply and build up on your skin surface, resulting in psoriatic lesions.

A 2017 article reported on new research that has identified the interaction of particular T cells and interleukins already known to be involved in the development of psoriasis. As more specifics are known, it may become possible to develop new targeted drug treatments.

Treatment for psoriasis depends on the type and severity of the condition, your general health, and other factors.

Here are the various treatments that target specific factors in the immune system that cause inflammation. These are generally used when your psoriasis symptoms are moderate to severe. Note that the newer drugs are more expensive.

Older drugs

Two older drugs used to suppress the immune system and clear psoriasis symptoms are methotrexate and cyclosporine. These are both effective, but have toxic side effects when used long term.

Biologics

TNF antagonists

A more recent drug targets a substance that causes inflammation called Tumor Necrosis Factor (TNF). TNF is a cytokine made by immune system components such as T cells. These new drugs are called TNF antagonists.

Anti-TNF drugs are effective, but less so than newer biologics. TNF antagonist drugs include:

Newer biologics

More recent biologics target and block particular T cell and interleukin pathways involved in psoriasis. Three biologics that target IL-17 have been approved since 2015:

  • secukinumab (Cosentyx)
  • ixekizumab (Taltz)
  • brodalumab (Siliq)

Other drugs aim to block another interleukin pathway (I-23 and IL-12):

  • ustekinuman (Stelara) (IL-23 and IL-12)
  • guselkumab (Tremfya) (IL-23)
  • tildrakizumab-asmn (Ilumya) (IL-23)

T-cell inhibitors target T cells in the immune system. T cells are white blood cells that are involved in inflammation. A T-cell inhibitor approved for use in psoriasis is:

  • abatacept (Orencia)

These biologics have proven to be safe and effective. A 2017 review article described them as transformative for psoriasis treatment.

Having one autoimmune disease such as psoriasis puts you at risk for developing another autoimmune disease. The risk is increased if your psoriasis is severe.

The groups of genes that predispose you to develop an autoimmune disorder are similar across different kinds of autoimmune diseases. Some of the inflammation processes and environmental factors are also similar.

The main autoimmune disorders associated with psoriasis are:

  • psoriatic arthritis, which affects 30 percent of people who have arthritis
  • rheumatoid arthritis
  • celiac disease
  • Crohn’s disease and other bowel diseases
  • multiple sclerosis
  • lupus (systemic lupus erythematosus or SLE)
  • autoimmune thyroid disease
  • Sjögren’s syndrome
  • autoimmune hair loss (alopecia areata)
  • bullous pemphigoid

The strongest association with psoriasis is with rheumatoid arthritis.

The relationship of psoriasis to other autoimmune diseases is a topic of ongoing study. Also being studied is the association of psoriasis with other diseases and with higher death rates from those diseases.

The outlook for people with psoriasis is very good. The condition can’t be cured, but current treatments can usually keep symptoms under control.

Medical research is continuing to discover more specifics about the causes of psoriasis and other autoimmune disorders. These new discoveries then help in the development of new drugs that specifically target and block disease pathways.

For example, several more new drugs targeting interleukin-23 are now in clinical trials. Other new approaches are likely to come out of ongoing research on autoimmune disorders in general.

Talk with your doctor about participating in ongoing clinical trials and about new developments. You may also want to join an online psoriasis/PsA support group.