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Many people know the immune system plays an important role in the development of psoriasis.

Psoriasis is a lifelong condition that affects over 8 million people in the United States. Despite the prevalence of the disease, there is still a lot to learn about what causes it.

Most treatment and management strategies for psoriasis, including medications and lifestyle changes, focus on changing effects on the immune system. The immune system is also naturally affected by a range of factors.

This article explores five facts about the relationship between the immune system and psoriasis.

Healthcare professionals generally consider psoriasis as an autoimmune disorder, which means it develops when the immune system attacks normal, healthy cells in the body.

In psoriasis, immune cells, known as T cells, attack healthy skin cells. These T cells release signals that recruit other immune cells to create an inflammatory environment within the skin.

This causes the body to try to produce new skin cells faster than it needs to, resulting in extra skin cells piling on top of each other. This results in the characteristic red plaques associated with psoriasis.

However, this misdirection of the immune system may not be exclusive to the skin. Psoriasis often occurs alongside other autoimmune disorders, including:

  • arthritis
  • alopecia
  • thyroiditis
  • vitiligo

Autoimmune disorders are usually lifelong, although some cases of psoriasis that develop in childhood may resolve on their own.

Psoriasis tends to run in families, and a family history of the condition is considered a risk factor for the disease.

Researchers have found genes associated with the development of psoriasis in a region of the genome known as psoriasis susceptibility 1, or PSORS1. This gene accounts for up to 50% of the heritability — referring to the genetic component — of psoriasis and is usually associated with the condition developing earlier in life, typically before 40 years of age.

Genes in this region instruct the body to build proteins involved in the recognition of molecules called antigens, which trigger a person’s immune responses. Typically, these antigens occur on the surface of foreign invaders, such as bacteria or viruses.

However, mutations in these genes can cause the immune system to incorrectly identify their own cells as foreign, leading to what is known as autoimmunity.

Studies have identified several other genes that also contribute to the development of psoriasis. These genes regulate many different processes, including:

  • inflammation
  • T cell activity
  • skin cell growth

Several factors associated with psoriasis may affect the immune system.

Smoking

Studies suggest that a history of smoking may increase the risk of psoriasis by over 60%. It may also reduce a person’s response to treatment.

Many toxins found in cigarette smoke may affect immune function. Nicotine, in particular, might play a number of roles. Many immune cells, including T cells, have nicotine receptors, meaning they respond to nicotine in the body. Some research shows that the nicotine receptor regulates immune cell activity.

Cold weather

According to the National Psoriasis Foundation, healthcare professionals experts believe cold weather is often a trigger for psoriasis. However, this may actually be at least partly due to less exposure to sunlight during cold seasons.

Exposure to ultraviolet (UV) radiation and sunlight supports the body’s production of vitamin D and regulates immune cell activity in the skin. This is why psoriasis often flares up following less sun exposure. Some studies suggest that taking vitamin D supplements may improve psoriasis symptoms, but more research is needed.

Phototherapy, which involves targeted exposure to UV radiation, has a long history as a successful treatment for psoriasis and other skin conditions.

During cold seasons, people are also more likely to get sick with infectious illnesses such as the flu. These types of illnesses can cause psoriasis to flare up.

Stress and anxiety

There is a close relationship between stress and psoriasis. For some people, stress makes psoriasis worse, and psoriasis causes stress.

One study found that 36% of individuals with psoriasis experience anxiety, while another suggested stressful triggers may increase the risk of a psoriasis flare-up by almost two-fold.

Although researchers are still investigating the exact mechanisms behind this relationship, there is an association between long-term stress and inflammation and increased activation of immune cells.

According to the National Psoriasis Foundation, other lifestyle and environmental triggers for psoriasis include:

  • skin injuries
  • infections
  • alcohol use

The human gut is home to a diverse ecosystem of bacteria known as the microbiome.

When the microbiome becomes dysregulated, it can cause “leakiness” in the gut, which signals to the immune system that something is wrong.

This triggers inflammation throughout the body and may lead to the development or progression of psoriasis.

There has been increasing interest in the role of anti-inflammatory diets in managing psoriasis symptoms. For example, a 2018 study found that following an anti-inflammatory Mediterranean diet was associated with less severe psoriasis.

Some of the effects of diet on psoriasis may also be associated with weight. Having overweight or obesity is considered a risk factor for psoriasis.

The most common infectious trigger of psoriasis is Streptococcal infection. Infections are known to trigger psoriasis through systemic inflammation.

Widespread inflammation triggers many of the symptoms of COVID-19, particularly severe forms of the disease.

A study of over 1,300 people found that psoriasis was not a risk factor for COVID-19 or severe disease, reporting that 55% of those with psoriasis who had COVID-19 experienced a flare-up.

However, although treatment of psoriasis often involves the use of immunosuppressive drugs, studies have found no additional risk for the occurrence or severity of COVID-19 associated with the use of psoriasis medications.