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UVB and PUVA for Psoriasis

Artificial Sunlight for Your Skin


Updated December 22, 2007

Although phototherapy equipment is classified as a device rather than a drug, such equipment is usually seen in a doctor's office or obtained with a doctor's prescription. For these reasons, phototherapy is listed here under "Psoriasis Drugs".

Experiments with ultraviolet light and psoriasis date back to the 1920s. Since then, ultraviolet light has become a standard treatment for extensive psoriasis and is referred to as phototherapy.

Ultraviolet light is a part of the electromagnetic spectrum. A complete review of the physics of the electromagnetic spectrum is well beyond the scope of this article. But suffice it to say that ultraviolet light is invisible to the naked eye, yet contains enough energy to both treat and/or burn the skin.

The sun produces ultraviolet light (UV). Three types of UV light are UVA, UVB and UVC. The effects of UVA are essentially therapeutic for psoriasis while producing minimal burning. UVB can be therapeutic but also can cause sunburn. UVC is used as germicidal light. For example, you may see UVC bulbs in restaurants, operating rooms or laboratories to kill airborne bacteria, but it does not help psoriasis.

Modern phototherapy relies upon use of a small portion of UVB that is termed "narrow-band" UVB (NB-UVB). This small subset of UVB is effective at treating the skin with less burning potential than natural UVB rays. Phototherapy equipment can be ordered specifically with bulbs that emit only narrow-band UVB for both home and in-office, physician-directed treatments.

Taking a pill called psoralen can make the skin more susceptible to the effects of UVA. Psoralen plus UVA phototherapy (called PUVA) can be effective for psoriasis even when UVB fails. Oral psoralen can have side effects such as nausea and the sensitivity to UV for both skin and eyes remains in the body for about 24 hours after it is taken. That means you should wear sunscreen, hat, long sleeves and dark sunglasses the entire day of treatment. This makes the logistics of PUVA somewhat daunting.

Topical medicines such as coal tar are often used for UVB phototherapy to enhance its effectiveness, again by making the skin more sensitive to UV.

A typical course of NB-UVB works something like this:

  1. patient is a candidate for systemic therapy (more than a cream) based upon severity of disease
  2. other medical reasons prohibiting phototherapy are absent
  3. patients medication list is reviewed for photosensitizing meds
  4. patient is selected for phototherapy, the risks as well as benefits explained, and consent obtained
  5. patient takes NB-UVB treatments 3 to 5 times weekly
  6. dosage (time of exposure) to NB-UVB is typically increased each visit
  7. after approximately one month, they usually show improvement
  8. after approximately two months, many patients are clear of psoriasis
  9. patient may elect to continue therapy once weekly to maintain their improvement, or spend time outdoors every weekend to expose their psoriasis to natural UV radiation to do the same.

Phototherapy is an effective treatment for patients with severe or extensive psoriasis where application of topical medicines is not practical or effective. There is limited or no internal side effects to phototherapy verus pills or injections. Care must be taken to avoid treating patients with medical reasons to avoid phototherapy such as medications which make them sensitive to sunlight.


Camisa C. Handbook of Psoriasis, 2nd Ed. Blackwell Publishing, USA 2004.

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