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People began using ultraviolet (UV) light in the form of sunlight to treat psoriasis centuries ago, and most psoriasis patients still find that their symptoms improve during the sunnier months of the year. But these days, light therapy, or phototherapy, for psoriasis can involve exposure to specially designed UV lamps in the setting of a dermatology clinic. There are three types of artificial UV light therapy: broadband UVB (BB-UVB), narrowband UVB (NB-UVB), psoralen plus UVA (PUVA), the excimer laser, and the excimer lamp.
Each is quite effective at improving psoriasis, but for a variety of reasons discussed further below—including insurance reimbursement issues, PUVA’s cancer risks, and the emergence of new alternatives—UV therapies appear to be losing popularity as a treatment option. Yet each of these therapies has particular benefits, and UVB especially deserves strong consideration for anyone seeking relief from troublesome psoriasis. Those who respond well to UV therapy can also consider purchasing a home unit. Some insurers will even cover the cost of home units where the need and effectiveness can be demonstrated. Administering UV light at home should, of course, continue to be done in close consultation with your physician.
Background on Types of Light
Light travels in waves, and different types of light can be distinguished from one another by the “width” of the waves (the distance from the peak of one wave to the peak of the next).  This distance, called wavelength, is usually measured in nanometers (nm), or billionths of a meter. UV light used for phototherapy has wavelengths in the range of 280-400 nm, with BB-UVB (280-320 nm), NB-UVB (primarily 311-313 nm), and UVA (320-400 nm) covering different subsets of that range. The excimer laser and lamp deliver light at 308 nm, which is in the UVB range. For comparison, commercial sun tanning beds use primarily UVA light.
Broadband UVB (BB-UVB) and Narrowband UVB (NB-UVB)
What are they? BB-UVB and NB-UVB treatment differ only in the wavelength of light used. As the names suggest, BB-UVB lamps emit a broad range of light wavelengths (280-320 nm), whereas NB-UVB lamps emit light in a narrow band, primarily at 311-313 nm, the wavelengths that have been shown to treat psoriasis most effectively with the fewest side effects. BB-UVB therapy has been used since the 1920’s; NB-UVB therapy was introduced in Europe in 1984, but was not available in the U.S. until 1998.
How are they administered? Patients usually receive treatments three times a week for several months at a dermatologist’s office or clinic. Before beginning treatment, patients are generally evaluated to determine the maximum amount of light they can tolerate without developing erythema, or reddening of the skin (the Minimal Erythema Dose (MED)). Treatment begins at a lower exposure (50% MED, for example), and the exposure is gradually raised. Because of the possibility that prolonged UVB treatment might increase the risk of skin cancer (see below, Drawbacks), doctors try to limit total UVB exposure and recommend short courses of treatment. To improve effectiveness, both BB-UVB and NB-UVB are sometimes used in combination with topical treatments such as vitamin D3 analogues (calcipotriene) or retinoids (tazarotene) or with systemic retinoids (acitretin).
How well do they work? NB-UVB is superior to BB-UVB for treating plaque psoriasis. NB-UVB is more effective overall, and it works well even at doses significantly below the MED, so patients experience fewer side effects. One review of the available clinical trial data concluded that psoriasis clears completely for 63-80% of patients who use NB-UVB; another similar review found that 55% of patients experience a 75% reduction in psoriasis severity (PASI75) after 12 weeks of treatment. Clearance can take a while—most patients need 15 to 20 treatments to see a 50% reduction in psoriasis severity, which corresponds to 5 – 7 weeks if following the typical three times per week treatment schedule. Comparisons of NB-UVB and PUVA have had mixed results, but PUVA is probably the more effective of the two treatments, by a small margin.
Advantages BB-UVB and NB-UVB have a significant safety advantage over most other psoriasis therapies, because side effects are limited to the skin. This makes UVB a popular choice for pregnant women, for example. The most serious potential side effect—skin cancer—has not been clearly demonstrated. (PUVA, by contrast, has a well-documented link with skin cancer.)
Drawbacks The possibility that UVB treatment increases the risk of skin cancer cannot be dismissed, although so far solid evidence is lacking. All patients receiving UVB should have annual skin cancer checks and keep their total UVB exposure as low as possible. Patients at high risk for skin cancer, including those with fair skin and those who have had skin cancer in the past, should be especially careful.
The most common side effect of UVB therapy is erythema, a sometimes painful reddening of the skin similar to sunburn. The dosage of UVB that causes erythema varies from patient to patient. Determination of an acceptable UVB dose on an individual basis helps to minimize this side effect.
UVB therapy can be time-consuming and inconvenient because it requires travel to a dermatologist’s office or clinic several times a week. With some insurers, UV therapies can also prove to be quite costly for the patient, as substantial co-pays can be assessed three times a week for many months.
How do they work? UVB inhibits DNA synthesis, which may, in turn, inhibit the overgrowth of skin cells seen in psoriasis plaques. UVB also promotes the self-destruction of T lymphocytes, the immune cells that gather in psoriasis plaques and trigger inflammation. Finally, UVB increases cellular production of several substances that reduce inflammation. Some combination of these mechanisms may explain how UVB exposure controls psoriasis.
Psoralen plus UVA (PUVA)
What is it? PUVA is a two-part therapy, consisting of exposure to psoralen followed  by exposure to UVA light. UVA light activates psoralen (methoxsalen, 8-methoxypsoralen, 8-MOP, Oxsoralen-Ultra), triggering its anti-psoriasis effects. Psoralens occur naturally in some plants and from as early as 1400 BC, people have used a combination of psoralen-containing plant extracts and sunlight to treat skin diseases. Modern PUVA therapy for psoriasis was developed in the 1970’s. There are many different psoralens, but the one used most often in PUVA therapy is methoxsalen, also known as 8-methoxypsoralen.
How is it administered? Patients can take psoralen orally, 1-3 hours prior to UV light treatment (systemic PUVA); alternatively they can soak for 15 minutes in a bath containing a dilute psoralen solution (bath PUVA). Regardless of the form of psoralen administration, the patient is then exposed to UVA-emitting lamps. Treatments take place two or three times a week in a dermatologist’s office or clinic. After psoriasis clears, patients may switch to a maintenance regimen of less frequent treatments. However, limiting total PUVA exposure is important because of the risk of skin cancer (see below, Drawbacks). PUVA is sometimes used in conjunction with methotrextate, acitretin, or UVB.
How well does it work? PUVA is considered highly effective, with 70-90% of patients experiencing partial or complete clearing of their psoriasis. One analysis of multiple clinical trials estimated that a 75% reduction in severity (PASI75) occurred in 63% of patients after 12 weeks of PUVA therapy. PUVA is significantly more effective than BB-UVB and probably slightly more effective than NB-UVB.
Advantages PUVA is an effective treatment for most psoriasis patients, and often sets in motion a remission in symptoms that last many months, even without maintenance therapy. Its effectiveness even in severe psoriasis -- allowing patients to restore a high quality of life -- helps it keep a place in the treatment arsenal. As the authors of a head-to-head study of PUVA vs. NB-UVB put it: “Compared with NB-UVB, PUVA achieves clearance in more patients with fewer treatment sessions and results in longer remissions.”
Drawbacks Patients who undergo PUVA therapy are at a higher risk of skin cancer, and the risk increases with the total dose of PUVA received. According to one study, patients who received 260 or more PUVA treatments had an 11-fold greater risk of squamous cell carcinoma and a somewhat increased risk of basal cell carcinoma as compared to patients who received 160 or fewer PUVA treatments. Usually, squamous and basal cell carcinomas are relatively non-aggressive cancers and are treatable if detected early. However, PUVA may also put patients at risk of melanoma, a much more aggressive and potentially deadly form of skin cancer. The skin cancer risk persists for decades after completing PUVA treatment, so patients need to keep up with a long-term schedule of skin cancer monitoring. Also because of cancer risk, men must protect their genitals from exposure during PUVA treatments.
PUVA can also cause erythema (a sunburn-like reddening of the skin) and nausea. Switching to a different psoralen, called 5-MOP, reduces nausea for some patients.
PUVA is not recommended for children under 12 or pregnant women.
Like UVB therapy, PUVA therapy requires traveling to a doctor’s office or clinic several times a week, which some patients may find very inconvenient.
Finally, the UV-sensitizing effects of psoralen persist for several hours, so patients must protect their skin and eyes from sun exposure (i.e., long sleeves and wrap-around, UV-blocking sunglasses) for about 24 hours following PUVA treatments.
How does it work? UV light-activated psoralen binds to DNA and forms tight links between the two strands of the DNA double helix, inhibiting DNA synthesis. PUVA treatment may, therefore, stop the abnormal proliferation of skin cells in psoriasis plaques by preventing the cells from duplicating their DNA. PUVA may also have suppressive effects on the immune cells that cause inflammation in psoriasis plaques.
308 nm Excimer Laser and Lamp
What are they? The 308 nm excimer laser delivers high frequency pulses of 308 nm (UVB) light in a 14-30 mm diameter spot. It is mounted on a maneuverable arm so that the beam can be aimed directly at a psoriasis plaque, sparing surrounding healthy skin. The first study demonstrating the effectiveness of laser treatment for psoriasis appeared in 1997, and the first laser specifically approved by the FDA for psoriasis treatment came on the market in 2000. The excimer laser technology is similar to that used for LASIK eye surgery. The 308 nm excimer lamp is a simpler device that also emits a small spot of 308 nm light that can be aimed; however, the light emission is continuous rather than pulsed and does not have the special properties of laser light.
How are they administered? Treatments are administered in a dermatologist’s office or clinic, typically twice-weekly for several weeks. Because 308 nm laser and lamp treatments spare healthy skin, they can be administered at higher doses than other UV treatments.
How well do they work? In the one study that directly compared the 308 nm laser, the 308 nm lamp, and NB-UVB, all three therapies had similarly good results. The treated psoriasis plaques cleared up in an average of 24 sessions. In some patients, the plaques remained clear for 4 months after treatment ended, and on average, there was only slight reoccurrence during the 4 months of follow-up. Other small studies have shown even quicker response times, but larger studies and more studies that directly compare the various forms of phototherapy are needed.
Advantages The main advantage of the 308 nm laser and lamp is that both can be aimed directly at psoriasis plaques, sparing healthy skin from UV radiation damage. The total amount of UV radiation to which the body is exposed is lower than with other forms of UV therapy, which may lower the risk of developing skin cancer. For this reason, 308 nm laser or lamp therapies may be good treatment options for children. In addition, the light dosage can be determined based on how the psoriasis plaque responds rather than on how surrounding healthy skin is affected. Because psoriasis plaques can tolerate higher doses of UV than healthy skin, higher doses can be used, possibly achieving better results.
The 308 nm laser and lamp also enjoy the same safety advantage as other forms of UVB therapy—they do not involve taking medication internally and side effects are limited to the skin; and UVB has a decades-long safe track-record. Finally, the treated sites often remain psoriasis free for months after the treatments are complete.
Drawbacks At the doses typically used today, the major short-term side effect of 308 nm laser and lamp treatment is reddening of skin at the site of treatment. Patients can also experience some blistering. At higher doses no longer commonly administered, blistering and pain were more frequent.
In the long-term, patients may be at higher risk of developing skin cancer at treated sites.
The advantage of 308 nm laser or lamp treatments—the ability to focus on small areas of skin—can also be a drawback. These therapies cannot be used on large areas of the body and therefore are not practical for patients with extensive psoriasis (involving >20% of body surface area).
As with all forms of phototherapy, 308 nm laser and lamp treatments require repeated visits over several weeks to a dermatologist’s office or clinic, which may be inconvenient for some patients.
How do they work? Like other UVB therapies, the 308 nm laser and lamp inhibit DNA synthesis and damage DNA. These effects block overgrowth of skin cells and induce the self-destruction of T lymphocytes in psoriasis plaques. T lymphocytes are especially vulnerable to 308 nm light. As compared to the 311-313 nm light used in conventional NB-UVB therapy, the dose of 308 nm light needed to kill T lymphocytes is much lower.
OTHER OPTIONS
Commercial tanning beds/tanning salons
There are two schools of thought on the use of commercial tanning salons for  psoriasis treatment. Critics note that commercial beds emit primarily UVA light, which is not very effective for psoriasis unless prescription psoralen is ingested or topically applied first. In addition, they argue, there is no medical supervision at commercial tanning salons, and the ‘sunburns’ that can occur through accidental overuse can actually worsen psoriasis. Supporters respond that for some patients who cannot afford alternate treatments or UV treatments in a medical setting, commercial tanning beds may offer a viable route to achieve improvement in psoriasis symptoms. Also, for those in rural areas or who are otherwise not able to access medical centers with UV light booths, commercial beds may be the only realistic option.
Clearly, commercial tanning salons are inferior to UV-light boxes designed specifically for psoriasis treatments, but the fact is some people use commercial tanning salons and do see improvement in their psoriasis.
Natural sunlight -- the sun
For most people with psoriasis, natural sunlight improves the skin symptoms of psoriasis (but not psoriatic arthritis, of course). Be sure to check in with your physician first, as some medications (and even nutritional supplements or alternative remedies) may make you more sensitive to sunlight. Also, take steps to avoid sunburn, which can make your psoriasis worse. Of course, with psoriasis, nothing is easy: for some, eve moderate amounts of sunlight worsens their psoriasis.
The Dead Sea
Some people who can afford to do so, visit the Dead Sea for weeks-long sessions where they sunbath  in the Sea’s unique waters to treat their psoriasis. The results are reportedly impressive. While experts believe it is primarily the sunlight that is having the beneficial impact, rather than the Dead Sea water itself, people who have gone there report that being on the beach among many other psoriasis patients itself has positive effect on one’s mind, if not body.
Conclusion
UV light in its many forms offers highly-effective treatment for most psoriasis patients. It should be pursued under doctor supervision, with careful attention to minimizing its risks, particularly avoiding burns and limiting total dose over time as much as possible. Some insurance coverage policies are undermining these treatment options through excessive co-pays on a per-visit basis. But UV light is likely to continue to be a promising option for certain populations, including children, pregnant women, and people who have other health conditions that block them from using some of the pills and injections that psoriasis patients use.
Living with psoriasis is often an ongoing experience with being ‘different,’ and UV light is a case-in-point. While most people are now hiding behind hats, long-sleeves and sunscreens to avoid the very real dangers of exposure to UV rays, people with psoriasis continue to seek out ultraviolet light for its healing properties.
But ironically, one of the least expensive and more effective ways to improve one’s psoriasis -- exposure to natural sunlight -- also puts many psoriasis patients in a bind: it requires us to expose our psoriasis to the world, and perhaps endure stares and other unwelcome attention.
As we reduce the stigma and perceived ‘unusualness’ of psoriasis with the general public, then, we will make it easier for psoriasis patients to make use of the free and abundant treatment offered outside on every sunny day.
Selected References
Fairhurst, DA et al. “Optimal Management of Severe Plaque Form of Psoriasis.” American Journal of Clinical Dermatology. 2005; 6(5):283-94.
Kollner, K et al. “Comparison of the 308-nm excimer laser and a 308-nm excimer lamp with 311-nm narrowband ultraviolet B in the treatment of psoriasis.” British Journal of Dermatology. 2005 Apr; 152(4):750-754.
Naldi, L and Griffiths, CEM. “Traditional therapies in the management of moderate to severe chronic plaque psoriasis: an assessment of the benefits and risks.” British Journal of Dermatology. 2005 Apr; 152(4):597-615.
Leon, A et al. “An attempt to formulate an evidence-based strategy in the management of moderate-to-severe psoriasis: a review of the efficacy and safety of biologics and prebiologic options.” Expert Opinion in Pharmacotherapy. 2007 Apr; 8(5): 617-632.
Lowe, JL et al. “Photo(chemo)therapy: General Principles.” Clinics in Dermatology. 1997; 15:745-752.
Passeron, T et al. “Use of the 308-nm excimer laser for psoriasis and vitiligo.” Clinics in Dermatology. 2006; 24:33-42.
Sami S. Yones; Roy A. Palmer; Trish T. Garibaldinos; John L. M. Hawk. "Randomized Double-blind Trial of the Treatment of Chronic Plaque Psoriasis: Efficacy of Psoralen-UV-A Therapy vs Narrowband UV-B Therapy." Arch Dermatol 2006 142: 836-842
Information on drug approval from the Food and Drug Administration’s website.
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