Psoriasis seems to have strong genetic and autoimmune components. Internal and external factors, including extreme temperatures and stress, may trigger a flare-up.

Psoriasis is a chronic inflammatory condition that causes recurrent discolored skin patches and silvery plaques on different areas of the body.

Psoriasis patches can range from a few flaky spots to large, scaly areas. They usually come and go in phases, flaring for a few weeks or months, then disappearing for a time, or even going into complete remission.

Contributing factors for psoriasis may be both internal and external. These can increase the chance of developing the condition or experiencing a flare if you already have it.

Although more research is needed, experts have narrowed down the following factors as possible causes and triggers of psoriasis.

The cause of psoriasis has yet to be established, although researchers suspect a strong genetic component is involved.

Experts have observed that some genes are commonly associated with the condition and that an autoimmune element also mediates its development. The term “autoimmunity” refers to the immune system attacking the body’s tissues when it mistakes them for foreign entities.

You may be more likely to have psoriasis if a close relative, like a parent, has it.

New psoriasis lesions can appear on expected and unexpected areas of your skin as a result of vaccinations, sunburns, scratches, or other skin injuries. This is called the Koebner phenomenon.

Persistent irritation may also lead to a psoriasis lesion. For example, in places where you usually wear tight clothing or accessories that rub your skin.

Certain infections, including strep and HIV, may increase your chance of developing certain types of psoriasis. The condition may also be more severe in people with compromised immune systems.

Children and young adults with recurring infections, such as strep throat or upper respiratory infections, also have an increased risk of severe psoriasis.

Other infections that may trigger psoriasis include:

Some medications are associated with the development of psoriasis or may worsen existing symptoms. For example:

  • Lithium can make existing psoriasis lesions worse.
  • Antimalarial drugs can cause psoriasis flare-ups about 2 to 3 weeks after you start taking the medication.
  • Beta-blockers can worsen psoriasis in some people.
  • Quinidine and indomethacin (Tivorbex) may aggravate psoriasis in some people.

Research indicates that obesity is a common risk factor for psoriasis onset. It may also worsen existing symptoms.

Weight management can affect psoriasis lesions. Losing weight if you have obesity or overweight may relieve or resolve psoriasis symptoms.

Some people find that other things trigger their psoriasis symptoms, such as:

  • Temperature: Extreme temperatures — both cold and hot — as well as dryness and humidity may trigger psoriasis. Even though sunlight is often recommended for psoriasis, exposure to high temperatures or direct sun rays may worsen symptoms.
  • Alcohol use: High alcohol consumption is associated with flare-ups.
  • Stress: Chronic emotional and physical stress can facilitate the development of psoriasis in some people, particularly those with weakened immune systems.
  • Smoking: Tobacco use has also been associated with an increased chance of developing psoriasis and a decrease in the effectiveness of some psoriasis medications, like biologics.

The causes of psoriasis aren’t entirely known, but risk factors and triggers are well documented. Medication side effects, exposure to extreme temperatures, dry and humid air, infections, and skin trauma are common risk factors.