Psoriasis and psoriatic arthritisPatient friendly summary

  • UVB light may reduce psoriasis risk by producing vitamin D. However, there is little evidence to support this idea.
  • UVB light is often used to treat psoriasis and reduce symptoms.
  • Vitamin D may reduce the symptoms of psoriasis in several ways.

Psoriasis is a common skin condition. It causes skin redness and irritation. Most people with psoriasis have thick, red skin with flaky, silver-white patches. These patches are called scales.

Psoriasis may lead to psoriatic arthritis in 10-30% of all cases. The symptoms of psoriatic arthritis can include swelling of tendons and joints. The fingers and toes may swell up like sausages.

Risk factors

Psoriasis is triggered by genetic and environmental risk factors. People of Northern European ancestry have higher rates of psoriasis than those of African or Asian ancestry. Environmental risk factors include:

  • Smoking
  • Stressful life events or trauma
  • Infections
  • Pregnancy
  • Drugs

Sunlight exposure and psoriasis risk

Sunlight may reduce the risk of psoriasis. There are lower rates of pediatric psoriasis in southern California than in other areas. The lower rate could be due to more sunlight exposure. It could also be due to fewer non-Hispanic whites in the population.

Vitamin D and Psoriasis

Vitamin D levels

There are reported studies linking vitamin D levels to a lower psoriasis risk. However, vitamin D is used to treat psoriasis. Therefore, higher vitamin D levels may reduce psoriasis risk.

How vitamin D works

Ultraviolet-B (UVB) light and vitamin D reduce the symptoms of psoriasis. The active form of vitamin D, calcitriol, offers several benefits:

  • Adjusts cell growth and maturation
  • Helps regulate the immune system

Topical calcitriol analogues (substitutes) are used to treat psoriasis. These agents are put on the skin. Topical calcitriol stops skin cells from multiplying, normalizes cell growth, and regulates immune cells.

Calcitriol substitutes reduce the number of dendritic cells and help them away from the skin, thereby lowering immunity and contact hypersensitivity responses. In addition, topical calcitriol may also increase regulatory T cells in the lymphatic tissue.


Vitamin D has not been shown to reduce the risk of psoriasis. However, it is a possibility.


UVB light is a preferred method of treatment for psoriasis.  Results from several treatment studies are presented here:

  • In previous times, people sometimes went to the Dead Sea to treat psoriasis using a treatment called heliotherapy. At least three hours of sun exposure daily for a month significantly reduced symptoms.
  • Currently, artificial UVB is used with good results. Some people use narrow-band UVB, while others use broadband UVB. The skin produces vitamin D from UVB and converts vitamin D to calcitriol.
  • One study found that using a combination of UVB light plus topical calcitriol was more effective than using either alone.

Find out more...

We will be adding a detailed evidence summary on this topic in the near future.  Please check back soon to find out more.

Page last edited: 17 May 2011