Phototherapy for psoriasis

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Phototherapy for psoriasis

Treatment Overview

Phototherapy is the use of ultraviolet (UV) light to slow the rapid growth of new skin cells. This is helpful in treating psoriasis, which causes skin cells to grow too rapidly. There are two types of ultraviolet (UV) light therapy:

Ultraviolet B (UVB)

UVB light is more effective than UVA light for treating psoriasis.

  • Exposure times start at 30 to 60 seconds and are gradually increased until light causes the skin to turn red. When the skin no longer turns red after this much exposure, the time is increased.
  • Treatments are given daily or several times a week.
  • UVB light is used alone, with tar products (Goeckerman treatment), or with dithranol applied to the skin (Ingram regimen).

Ultraviolet A (UVA)

UVA penetrates deeper into the skin than UVB.

  • Treatment with UVA typically takes 20 minutes for a session.
  • UVA light used with psoralen drugs is called PUVA. With PUVA, the treatment time is greatly reduced, from 20 minutes to about 2 minutes.

Phototherapy may be given at locations such as a hospital or doctor's office, a psoriasis daycare centre, or your home (UVB).1

Phototherapy can be used alone or with medicines. UVB light therapy is used alone to treat severe psoriasis. Typically, when medicines for psoriasis are used with light therapy, you will use or take the medicine first. You may apply it to your skin, take it by mouth, or use it as bath salts in water. Then you will go into a booth and be exposed to the UV light. Using two kinds of treatment is called combination therapy. Three common combination therapies are:

  • Psoralen and UVA light therapy (PUVA), which combines UVA exposure and a medicine (called a psoralen) that makes your skin more sensitive to light.
  • The Ingram regimen, which combines dithranol, coal tar products, and UVB phototherapy.
  • The Goeckerman treatment, a combination of tar products and UVB phototherapy.

Your body is exposed to UV light from banks of light tubes that give off either UVB or UVA light in a booth. Booths come in several designs. Some look like phone booths and you can stand in them. Others look like tanning beds and you can lie down during treatment. The booth will record the total amount of light you are exposed to.

In general, your entire body is exposed to the light. (If psoriasis affects only certain areas of your body, UV light may be directed at these selected areas only.) You will wear sunglasses that block UV light and goggles or a blindfold to protect your eyes from getting cataracts. Men may also need to shield their genitals to protect them from an increased risk of genital cancer.

One phototherapy option includes the use of narrow-band UVB light. This exposes you to only the wavelengths of light that work for treating psoriasis. Older UVB lights exposed the person being treated to ineffective wavelengths of light in addition to the effective wavelengths.

What To Expect After Treatment

As your skin recovers from treatment, it should be checked at least once or twice a year for signs of skin damage or skin cancer.

Why It Is Done

PUVA (the use of psoralen medicines with UVA light therapy) is usually used when psoriasis is disabling and safer treatments have not worked.

UVB light alone (without drugs) is used for widespread plaque psoriasis and guttate psoriasis.

How Well It Works

Phototherapy is usually an effective treatment for psoriasis.2 Partial to full skin clearing occurs after an average of 20 clinic treatments. More severe psoriasis may require more treatments. Using home equipment, which is less powerful than equipment at a clinic, takes 40 to 60 sessions to clear the skin.

Doses of UVB high enough to cause the skin to turn red, used with petroleum jelly (such as Vaseline) or other moisturizers, can clear psoriasis plaque.

When using UVA alone, treatments may be helpful but take much longer to clear psoriasis. UVA is very effective when used with a photosensitizing drug (psoralen). This combination treatment is called PUVA.


Risks of phototherapy include:

  • Skin cancer. UVB is the part of sunlight that causes suntans, sunburns, skin damage, and aging. Exposure to UVB light can also lead to skin cancer and can cause serious eye damage. The risk of skin cancer increases with the amount of exposure to UV light. Your dermatologist will monitor your overall exposure to UV rays.
  • Skin damage. Long-term exposure to UVA light may lead to skin damage, aging, skin cancer, and cataracts. This risk of cataracts can be reduced by regular use of sunglasses that block UVA light when you are outdoors.
  • Cancer. The male genitals are highly susceptible to the cancer-causing effects of both PUVA therapy and UVB therapy.

UVA produces fewer and milder short-term side effects than UVB.

What To Think About

Phototherapy requires a lot of time for treatment, and UV booth equipment is expensive. Commercial tanning beds, which emit UVA, are less effective for psoriasis than UV booths.

For people who have erythroderma or pustular psoriasis, UV treatment may make the condition worse.

The U.S. National Psoriasis Foundation provides information on where you can buy home light therapy equipment. Home light therapy should only be done under your doctor's supervision. For more information, see the organization's Web site at

Complete the special treatment information form (PDF) (What is a PDF document?) to help you understand this treatment.



  1. Koek MBG, et al. (2009). Home versus outpatient ultraviolet B phototherapy for mild to severe psoriasis: Pragmatic multicentre randomised controlled non-inferiority trial (PLUTO study). British Medical Journal, 338: b1542.
  2. Habif TP, et al. (2005). Psoriasis and other papulosquamous diseases. In Skin Disease: Diagnosis and Treatment, pp. 106–115. Philadelphia: Elsevier Mosby.


By Healthwise Staff
Primary Medical Reviewer Kathleen Romito, MD - Family Medicine
Specialist Medical Reviewer Alexander H. Murray, MD, FRCPC - Dermatology
Last Revised February 15, 2010

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information.