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What is phototherapy?

Phototherapy is a common and effective treatment option for psoriasis. Phototherapy uses ultraviolet (UV) light under medical supervision to treat certain skin diseases.

Phototherapy is a common and effective treatment option for psoriasis. Phototherapy uses ultraviolet (UV) light under medical supervision to treat certain skin diseases.

Why it's done

Because UV light can suppress the immune system, phototherapy is used to decrease the inflammation associated with skin conditions responsive to this therapy. Skin disorders that can be treated with phototherapy include psoriasis (including scalp psoriasis), eczema, vitiligo, itching and cutaneous T-cell lymphoma.

Our approach

Phototherapy can be used alone or in combination with topical or systemic medications, depending on each patient’s unique case and needs. Phototherapy is predominantly an office-based procedure, but patients with chronic skin conditions who become more experienced with the procedure and who are comfortable in self-administering light therapy can be prescribed a unit to use at home.

Types of treatment

Common types of UV light treatment include:

  • Broad-band UVB light - (280–320-nanometer wavelengths)
  • Narrow-band UVB light - (311-nanometer wavelength only)
  • UVA light - (320–400-nanometer wavelengths of light)
  • PUVA, a type of UVA light therapy combined with an oral light-sensitizing medication known as psoralen - (320–400-nanometer wavelengths of light)

Generally, UVB light alone is the common treatment for psoriasis. PUVA is usually used in extreme cases and when other treatments have not worked.

Of the two types of UVB treatments, narrow-band is a faster and more effective treatment for psoriasis. It can also be more effective in fewer sessions and result in longer remissions than broad-band UVB. 

UVA light therapy on its own often takes much longer to clear psoriasis, though treatments may be helpful. PUVA therapy is typically much more effective, as it slows down excessive skin cell growth. PUVA is the most effective treatment for plaque psoriasis.

Because indoor tanning can increase the risk of melanoma by 59 percent, the National Psoriasis Foundation advises against the use of indoor tanning beds as a substitute for phototherapy.


Phototherapy is a painless treatment similar to going to a tanning salon. However, there are risks associated with it, including skin damage and cancer. Due to the repeated exposure of UV rays, phototherapy can contribute to skin aging and increases your risk for cancer. It is not recommended for those with a history of skin cancer.

What to expect

UVB is present in natural sunlight and is an effective treatment for psoriasis. During UVB phototherapy, UVB light penetrates the skin and slows the growth of affected skin cells.

During your first UVB phototherapy sessions, your skin is exposed to UVB for 30 to 60 seconds at a time until it turns slightly pink. Exposure time is increased when the skin becomes more resistant and does not turn pink as quickly. UVB treatments take place several times per week until the psoriasis is cleared.

UVA treatment penetrates deeper into the skin than UVB. It can typically take 20 minutes per session. PUVA treatments are much shorter at around two minutes.

Home equipment is less powerful than the equipment used at clinics, and therefore home treatment takes longer. It typically takes 40 to 60 sessions to clear the skin with home phototherapy treatments, whereas it usually takes 20 in-office treatments.

Follow-up care

After your treatment is complete, you should get a skin cancer screening at least once or twice yearly.

Possible side effects

Itchiness and redness are common side effects during UVB phototherapy treatments. UVA produces fewer and milder short-term side effects than UVB. Like UVB, PUVA treatments can also cause itching and redness of the skin, as well as swelling of the legs and nausea from the oral psoralen.

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