Last updated: May 19, 2009
Phototherapy is the original psoriasis treatment. For as long as people have had the disease, theyve treated it with sunlight. Even today, with all the high-tech remedies available, light therapy continues to be one of the most effective treatments for psoriasis, an autoimmune disorder that causes skin cells to grow too rapidly, resulting in red, itchy lesions on the surface of the skin.

“When ultraviolet light hits skin, it does all kinds of things,” says Steven Feldman, MD, PhD, a professor of dermatology at the Wake Forest University School of Medicine in Winston-Salem, N.C. Ultraviolet light kills the immune cells in the skin that contribute to psoriasis, and research suggests that UV light may also disrupt the faulty signals between immune cells and skin cells that lead to psoriasis lesions.

With relatively few side effects, phototherapy is an effective—yet underused—treatment, experts say. “Phototherapy is a great treatment to start with,” recommends Kathy Kavlick, RN, community outreach nurse for the Murdough Family Center for Psoriasis in Cleveland. “Some people get really good results from it.”

Types of phototherapy
Phototherapy is usually administered on an outpatient basis in a dermatologists office two to three times a week, using a walk-in light booth that looks like a tanning bed stood on end. Light boxes for home use are also available.

There are two main types of phototherapy:

  • Ultraviolet B light (UVB), one of the components of sunlight, is especially effective for treating psoriasis. During the treatment patients are exposed to the light for just a few seconds at first, and the exposure time is gradually increased to several minutes per treatment. UVB treatment is sometimes administered with topical treatments such as coal tar, anthralin, or just mineral oil. A form of UVB light known as narrow-band (NB-UVB) has been shown to be even more effective than UVB, and is increasingly being used by dermatologists.

  • Although not as potent as UVB, ultraviolet A light (UVA) is also used to treat psoriasis. UVA treatment generally takes longer than UVB—exposure times can reach 15 to 20 minutes—but at these higher doses it is also effective in clearing lesions. UVA light is often combined with an oral medication known as psoralen (a treatment known as PUVA).
  • A newer variation of phototherapy uses excimer or pulsed-dye lasers to target individual plaques. Research suggests that laser therapy may require fewer treatments and produce longer remissions, but since this technique is so focused it is not very practical for people with widespread lesions. As Dr. Feldman notes, however, roughly eight out of 10 people with psoriasis have lesions only in small, isolated spots, and laser therapy may grow more popular as the technology becomes faster and more effective.

    What works best
    Patients generally require about 20 phototherapy sessions before they see an improvement in their skin. Although response rates vary, studies suggest that 65% of the patients who receive UVB treatment and 75% of the patients who receive NB-UVB will experience significant skin clearance. Although UVB treatments are more widely used, PUVA may actually be more effective.

    In a 2006 study in the Archives of Dermatology that compared PUVA and NB-UVB therapy in patients with chronic plaque psoriasis, the patients who underwent PUVA therapy had a significantly higher clearance rate (84%) than those who received NB-UVB (65%). The former group also required fewer treatment sessions, and the effects lasted longer.

    PUVA does have some potentially serious side effects, however. Nearly one-third of patients experience nausea after treatment—and, more important, PUVA carries a long-term risk of skin cancer, especially in patients with fair skin.

    The psoralen molecule used in PUVA is believed to be largely responsible for the increased risk. Psoralen, which is ingested orally or applied topically, enters the bodys cells and, when activated by UV light, changes their DNA. This process kills off immune cells close to the skin and helps control psoriasis, but it also leads to collateral damage that can cause skin cancer in the long run.

    Because of the risk of skin cancer, PUVA is typically reserved for the most severe and stubborn psoriasis cases. “PUVA is a very, very effective treatment,” says Dr. Feldman. “Its at least as effective as narrowband UVB, but it causes an increased risk of skin cancer, so we tend to avoid using it.”

    UVB light is known to cause skin cancer as well, but studies have not shown any increased risk of skin cancer among psoriasis patients who have undergone UVB phototherapy.

    If its so effective, why isnt phototherapy used more?
    Although phototherapy is considered a first-line treatment for psoriasis, patients and dermatologists alike report that it is often impractical.

    Convenience is a factor, since patients need to visit their doctors office several times a week during business hours. But it can also be expensive; for each treatment, most insurance companies charge an office-visit co-pay, which tends to be higher than drug co-pays.

    Nikki Woistman, 21, of St. Petersburg, Fla., considered phototherapy several years ago when psoriasis covered about 30% of her body. She was surprised to learn, however, that phototherapy would actually be more expensive than the new generation of biologic medications.

    “Phototherapy was going to be $30 to $45 three times a week—and that adds up,” she says. “And it was a 30- to 45-minute ride [to get there], which didnt really work with my schedule.” Woistman was interested in a home unit, but insurance didnt cover it and her family couldnt afford to pay out of pocket (some units cost several thousand dollars).

    “Some dermatologists say phototherapy is threatened,” says Sheila Rittenberg, senior director of advocacy and external affairs for the National Psoriasis Foundation. “They cant keep the equipment up if patients arent using it, and some patients are being bumped up to more expensive treatments.”

    Tanning beds
    Many psoriasis patients use commercial tanning beds to manage their lesions, and the anecdotal evidence suggests that they can be effective. Tanning beds emit both UVA and UVB light, and the percentage of UVB varies widely by machine, from less than 1% to nearly 10%. Whatever benefit patients experience likely comes from the UVB.

    Many dermatologists believe that tanning beds are ineffective and potentially risky, since excessive use can cause skin damage and an increased risk of cancer. But if used responsibly, Dr. Feldman says, commercial tanning centers may be a “reasonable alternative” to phototherapy for patients without easy access to affordable office- or home-based treatments. (Consult a dermatologist before starting a tanning regimen, and review this list of precautions from the National Psoriasis Foundation.)

    Good old sun
    As people have known for thousands of years, natural sunlight is an effective treatment for psoriasis, although the effects may take several weeks to materialize. To avoid sunburn and overexposure, the National Psoriasis Foundation recommends multiple short sunbathing sessions. (Sunburns can actually exacerbate psoriasis.) Psoriasis patients should use sunscreen of SPF 15 or more on the parts of their bodies that arent affected by lesions, reapplying frequently.