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Psoriasis: Causes

Psoriasis is common. About 2% of people living in the United States have this condition.1

Most people who get psoriasis have white skin, but the condition develops in people of all races. Findings from studies indicate that psoriasis may be more common in skin of color than previously thought. In one US study, researchers found that 3.6% of whites, nearly 2% of African Americans, and 1.6% of Hispanics had psoriasis.2

Psoriasis runs in families

If a parent, grandparent, brother, or sister has psoriasis, you have a higher risk of getting it.

Happy family

What causes psoriasis?

Psoriasis runs in families: If a parent, grandparent, brother, or sister has psoriasis, you have a higher risk of getting it.

Psoriasis is not contagious. Unlike chickenpox or a cold, you cannot catch psoriasis from someone. 

You also CANNOT get psoriasis by: 

  • Swimming in a pool with someone who has psoriasis

  • Touching someone who has psoriasis

  • Having sex with someone who has psoriasis

While we know that psoriasis isn’t contagious, scientists are still trying to determine exactly how psoriasis develops. 

Scientists have learned that a person’s immune system and genes play a role in causing psoriasis. Here’s what studies have revealed about each of these. 

Immune system: White blood cells, also called T-cells, are part of the body’s immune system. These cells help prevent us from getting sick by attacking things that can harm us, such as bacteria and viruses. 

When a person has psoriasis, something goes wrong in the immune system, so T-cells also attack the body’s skin cells. This attack causes the body to make new skin cells more often. The extra skin cells pile up on the surface of the skin, and you see psoriasis. 

Once T-cells start to attack skin cells, this usually continues for the rest of a person’s life. There is one exception. Some children who get a type of psoriasis called guttate (gut-tate) psoriasis never have it again. 

Genes: We know that psoriasis runs in families. Scientists have found that people who have certain genes are more likely to get psoriasis. 

What complicates matters is what else scientists have learned. It’s seems that some people who get psoriasis don’t have genes that increase their risk of getting psoriasis.

It’s also possible to have genes that increase the risk of getting psoriasis and never develop psoriasis. It’s this discovery that led scientists to believe that the person must be exposed to a trigger before psoriasis appears. 

What can trigger psoriasis? 

Plenty of everyday things can act as a trigger, causing psoriasis to appear for the first time. Common psoriasis triggers include: 

  • Stress

  • Skin injury, such as a cut or bad sunburn

  • Infection, such as strep throat

  • Some medications, including lithium, prednisone, and hydroxychloroquine

  • Weather, especially cold, dry weather

  • Tobacco

  • Alcohol (heavy drinking)

These triggers can also cause psoriasis flare-ups. Different people have different triggers. For example, periods of intense stress may trigger your psoriasis but cold weather may not.

That’s why it’s so important for people who have psoriasis to know what triggers their psoriasis. Avoiding triggers can reduce psoriasis flares. 

You’ll find common triggers and what you can do to avoid them at: Are triggers causing your psoriasis flare-ups?

If you think you have psoriasis, it’s important to find out. Treatment can help relieve your discomfort and lead to clearer (or clear) skin. You can find out how board-certified dermatologists diagnose and treat psoriasis at: Psoriasis: Treatment.

Related AAD resources

1 Gottlieb A, Korman NJ, et al. J Am Acad Dermatol 2008;58:851-64.
2 Alexis AF, Blackcloud P. J Clin Aesthet Dermatol. 2014;7:16-24.

Getty Images

Alexis AF, Blackcloud P. “Psoriasis in skin of color: epidemiology, genetics, clinical presentation, and treatment nuances.” J Clin Aesthet Dermatol. 2014;7(11):16-24.

Gottlieb A, Korman NJ, et al. “Guidelines of care for the management of psoriasis and psoriatic arthritis Section 2. Psoriatic arthritis: Overview and guidelines of care for treatment with an emphasis on the biologics.” J Am Acad Dermatol. 2008;58(5):851-64.

van de Kerkhof PCM and Schlkwijk J. (2008) “Psoriasis.” In: Bolognia JL, Jorizzo JL, et al. editors. Dermatology, 2nd ed. Spain, Mosby Elsevier: p. 115.

Medical reviewers
Meet the board-certified dermatologists who reviewed this content. Each has conducted research that gives us a better understanding of psoriasis.