Phototherapy for Psoriasis

Phototherapy is the controlled use of ultraviolet light (UV rays) from natural or artificial sources to treat skin diseases, particularly psoriasis.

Different wavelengths of light produce different effects on the skin. For the treatment of psoriasis, both ultraviolet A (UVA) and ultraviolet B (UVB) are used. UVB phototherapy can be used alone or in combination with other treatments. UVA must be used with other medications to sensitize the skin, usually psoralen. The combined use of a psoralen and UVA is called “PUVA” (psoralen UVA).

Exposure to UVA and UVB light appears to alter the immune response in the skin and slow the growth of skin cells. This leads to a reduction in the build-up of skin plaques that create the psoriasis lesions.

Phototherapy can be time-consuming and inconvenient, but it’s an effective treatment for certain types of psoriasis and a useful alternative to other medications.

UVB Phototherapy

A UVB light is used in the doctor’s office or at home with a unit obtained by prescription. The person removes clothing as necessary to expose the affected skin to the light. Exposure time is based on the individual’s own skin response and should be just long enough to create a very slight redness. This treatment is repeated 3 to 5 times per week until the lesions clear. After as many as 25 or more treatments to get the psoriasis under control, maintenance therapy with less frequent treatments may be recommended.


PUVA combines UVA light and an oral dose of psoralen, which is taken one or two hours prior to exposure to the UVA light in a “light box.” The person disrobes, puts on UV-protective goggles to protect the eyes, and then stands or sits in the light box for the recommended amount of time.

Treatments are usually recommended for 2 to 4 times per week until the psoriasis clears. This may take 2 to 3 months and could be followed by a twice-monthly maintenance regimen to prevent a recurrence.

People undergoing PUVA therapy should avoid the sun as much as possible because psoralen makes the skin susceptible to sunburn and other damaging effects of sunlight. In addition, UV-protective sunglasses should be worn all day following a treatment.

PUVA is used primarily for plaque and guttate psoriasis. Erythrodermic psoriasis also responds to PUVA, but not as well as these other forms.

Side effects of phototherapy

UVB and PUVA share the risk of certain side effects:

  • Sunburn
  • Itching
  • Skin discoloration
  • Photoaging (premature wrinkling of the skin)
  • Increased risk of skin cancer
  • Eye damage if the eyes are not sufficiently protected
  • PUVA lentigines (brown spots that appear after prolonged use of PUVA)

Caring for your skin when undergoing phototherapy

People using any form of phototherapy should keep in mind the following:

  • Practice sun protection and use sunscreen after receiving phototherapy treatments to minimize the damaging effects of excessive UV exposure.
  • Use sunglasses with UV protection to avoid eye damage.
  • If you are sensitive to the sun because of a medical condition (lupus, porphyria) or medication (tetracycline, sulfa drugs), tell your doctor before starting treatment. 

Before trying a sunlight regimen of your own, seek the guidance of a doctor to make sure you don’t overexpose your skin and aggravate your symptoms.

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Last updated: 1/8/2019