3 Causes of Psoriasis

Genetics and environmental factors play key roles

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Psoriasis is a chronic autoimmune disorder characterized by patches of skin that are red, flaky, and itchy. It can vary in severity with some cases affecting only part of the body while others involve the entire body.  

There are five main types of psoriasis broadly defined by their appearance and the parts of the body they can affect:

  • Plaque psoriasis is the main type and has the features we typically associate with the condition: inflamed, red patches with silvery, flaky scales. The rash is most commonly seen on the back of the arms, scalp, shins, and around the navel.
  • Guttate psoriasis has scaly, teardrop-shaped spots that are more salmon-pink in color and appears mostly on the arms, legs, stomach, and chest. 
  • Pustular psoriasis is characterized by small, pus-filled blisters. The rash sometimes just appears on the palms or soles; at other times, they cover the entire body. 
  • Inverse psoriasis is a typically painful variation that affects folds of skin, such those under the armpits, genitals, breasts, or buttocks.
  • Erythrodermic psoriasis occurs when the rash becomes widespread and can be caused by any of the above-listed variations.

Autoimmune disorders are those in which the body's immune system turns on itself and inadvertently attacks healthy cells. In psoriasis, DNA released from dying skin cells triggers an immune response by which defensive white blood cells are suddenly directed to kill healthy cells in the area.  

While the exact cause of psoriasis is unknown, it is believed that a combination of factors contributes to the development of the disease.

Genetic Causes of Psoriasis

Researchers have found nine different gene mutations that may be involved in causing psoriasis. One of these mutations, called PSORS-1, appears to be a major factor. Mutations like these alter how certain cells normally function.

With psoriasis, the mutations seem to affect so-called "helper" T-cells, a type of immune cell which effectively points "killer" T-cells in the direction of tissues and cells they are meant to destroy.

Immune System Causes of Psoriasis

In a normally functioning immune system, white blood cells produce antibodies when in the presence of foreign invaders like bacteria and viruses. These white blood cells also produce chemicals that actively stimulate the immune defense. 

With psoriasis, the white blood cells suddenly become overstimulated. They start attacking the skin and set off a cascade of events that make the skin cells multiply so quickly as to accumulate on the surface. 

The cycle by which normal skin forms, matures, and dies takes around 30 days. But in psoriasis, the skin goes through this cycle in as little as three to six days. This increased pace results in the scaly rash we come to associate with psoriasis.

The overstimulation of these cells also causes the release of chemicals called cytokines which only add to the inflammation.

Environmental Causes of Psoriasis

Not everyone with a genetic propensity for psoriasis will get psoriasis. In some cases, activation of the underlying genetics only occurs in the presence of an environmental trigger.

These external triggers can include:

  • skin injury, including abrasions, sunburn, and drug rash
  • cold weather
  • stress
  • infection
  • low calcium
  • certain medications, such as ACE inhibitors, beta-blockers, and lithium

    Sources:

    Habif, T. "Psoriasis." Clinical Dermatology, 4th Edition. Ed. Thomas Habif, MD. New York: Mosby, 2004. 209-239.

    Smith, C., and Barker, J. "Psoriasis and its management." British Medical Journal. 2006; 333:380-384.

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