Ultraviolet A and B

Sunday, May 31, 2009  |  Updated 9:46 AM PDT
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Most people with psoriasis know that spending time in the sun can help clear up their skin. That's because the sun is the most common source of ultraviolet light. Ultraviolet A light primarily causes the skin to tan, while ultraviolet B light causes tanning and sunburns. Lamps that produce both types of light are sometimes used to treat moderate or severe cases of psoriasis.

Psoralen Plus Ultraviolet A
On its own, ultraviolet A does not have a significant effect on psoriasis. The medication psoralen makes the skin respond to ultraviolet A. Psoralen plus ultraviolet A (PUVA), also called photochemotherapy, involves a combination of the medication psoralen and ultraviolet A rays.

Therefore, the first step in a PUVA treatment is to either ingest psoralen pills two hours before the treatment or apply it by painting it on or soaking in a tub of water that contains psoralen about 15 minutes before the light treatment.

Light treatments last between 30 seconds and several minutes. Most people require treatments two or three times a week for a total of 20 or 30 treatments to clear the skin. After that, many people require maintenance treatments. For some people, one treatment a month is enough; others may need more frequent maintenance.

PUVA appears to be effective in 85 to 90 percent of patients. The treatment is especially helpful for people with stable plaque psoriasis, guttate psoriasis, which causes droplet-shaped lesions instead of larger patches of psoriasis, and psoriasis on the hands and feet.

The side effects of PUVA include nausea (from the oral medication), itching and skin redness. Long-term use of PUVA increases the risk of skin cancer. The treatment also can cause freckling, skin aging and cataracts. The increased risk of cataracts can be avoided if patients wear eye protection for 12 to 25 hours after ingesting psoralen.

Ultraviolet B
Ultraviolet B therapy involves coating the skin with an emollient such as mineral oil or petroleum jelly, and then exposing the skin to UVB light for brief periods, sometimes just a few seconds. Occasionally, medicated lotions, like anthralin-salicylic acid paste or pills, like retinoids, are used in combination with UVB therapy.

There are two types of UVB therapy: broadband and narrowband. Broadband therapy, which has been available for more than 80 years, involves a wide spectrum of UVB wavelengths. Patients require three to five treatments a week. Narrowband therapy is newer and involves a narrow band of UVB wavelengths. It is more effective than broadband treatment, requiring two to three treatments a week.

The skin usually clears up after about 15 to 25 treatments. Maintenance treatments, perhaps two a week, begin as soon as lesions reappear.

Although UVB treatment is less effective than PUVA, it has fewer side effects and is less likely to cause skin cancer.

Questions to ask your doctor:
1. How many treatments will I need?
2. Are there any lotions or medications I should avoid before treatments?
3. Will I need special screening for skin cancer after treatment?

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