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What Causes Psoriasis?

Causes of Psoriasis: The Role of Genes

One out of 10 people have genes that make them more likely to get psoriasis. But most people with psoriasis don't report having a relative with the disease. So while there are clearly genetic connections, they're not exactly clear-cut.

"It's not a simple genetic program like green eyes or blue eyes, where it passes through a family in a specific pattern," Evans says. "And it isn't a strictly genetic disease the way cystic fibrosis is." Think of it more as tendency toward disease, possibly brought on by a variety of genetic changes. For example, errors in DNA chemicals may lead to missing, misshapen, or misplaced proteins.

To actually develop psoriasis, you must have a combination of different genes. Researchers are still working to identify all of them. Once this happens, the causes of psoriasis will become much clearer.

A significant percentage of people have genes that predispose them to the disease. But only a fraction -- maybe 2% or 3% of the population -- develop psoriasis. It's likely that the tendency toward psoriasis requires certain triggers to get fully set into motion. "Whether that is environmental triggers or infections or other types of triggers is unknown," Evans says.

Causes of Psoriasis: The Role of Triggers

A wide range of triggers is linked with the onset or flare-up of psoriasis. These vary from person to person, but may include:

  • Stress
  • Medications
  • Infections
  • Injuries

"We know that injuries bring on psoriasis at the site of the injury," Evans says. "For example, if someone has a surgery, they will sometimes get psoriasis along the line of the scar." Called the Koebner phenomenon, this can also occur following vaccinations, bug bites, sunburns, or cuts. As many as half those with psoriasis experience this phenomenon. It provides a strong argument for protecting your skin, especially during summer months.

Some medications are also more likely to trigger a flare of psoriasis. They include:

  • Lithium, used to treat certain psychiatric disorders
  • Antimalarial medications
  • Certain high blood pressure or heart medications such as inderal or quinidine
  • Indomethacin, a nonsteroidal anti-inflammatory drug

"There can also be an onset after an infection such as strep throat, especially in young people," Evans says. Fortunately, treating the infection may help the flare-up to cool down.

Other triggers linked to psoriasis include allergies, diet, dry and cold weather, smoking, and heavy use of alcohol. But much more research is needed to complete the puzzle that makes up this complex disease.

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Reviewed on April 12, 2013

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