UVB Phototherapy for Psoriasis

Used for more than 75 years to treat psoriasis, UVB phototherapy continues to be an effective treatment. It works by exposing the skin to a type of ultraviolet (UV) light called UVB. The UVB light penetrates the skin, and this slows the rapidly growing skin cells that lead to psoriasis.

To receive UVB phototherapy, a person stands in a light box lined with UVB lights. UVB phototherapy usually takes place in a dermatologist’s office or psoriasis clinic. If UVB therapy proves effective, some people can use an at-home UVB unit prescribed by a dermatologist.

severe psoriasis

psoriasis patient after treatment

Before treatment - Patient with severe psoriasis

After treatment - The patient's dermatologist prescribed UVB phototherapy and an oral (taken by mouth) retinoid to clear this patient's psoriasis.

Photographs used with permission of the
 Journal of the American Academy of Dermatology. 

All photographs were published in the Journal of the American Academy of Dermatology, Vol. # 45,
Lebwohl M, Ali S. “Treatment of psoriasis. Part 1. Topical therapy and phototherapy,” 487-98; quiz 99-502. Copyright Elsevier (2001).

Number of treatments: UVB phototherapy requires time. To be effective, 2 to 5 treatments per week are given for several weeks. The exact number of treatments varies with the patient’s response, type of UVB phototherapy prescribed, and the severity of the psoriasis.

Some people need to pre-treat their skin. This can involve applying coal tar to the psoriasis the night before and washing it off in the morning. Before stepping into the light box, most people apply a thin layer of petroleum jelly or mineral oil to the psoriasis. This thin layer makes the UVB light more effective.

How long clearing lasts: Remission time varies. Recent studies suggest that it may be possible to increase clearing by continuing treatment for a bit after the skin clears. One such study found that more than half (55%) of the patients who did this were clear 1 year later. These patients received narrowband UVB phototherapy 3 times per week for 12 weeks. For the next 4 weeks, they received 2 UVB treatments per week. For the following 4 weeks, they received 1 UVB treatment per week.

Currently, most patients stop UVB phototherapy when their skin clears. Some begin the UVB treatments when the psoriasis starts to return.

Side effects: The skin may be red, itchy, or dry after UVB exposure. Some people develop a sunburn-like reaction and even blisters. Temporary worsening of the psoriasis also is possible before the skin starts to clear. Pregnant women may develop melasma, a skin condition that causes mottled skin.

Receiving years of UVB phototherapy may pose greater risks. Over time, exposure to UVB light may increase one’s risk of premature skin aging. Signs of premature skin aging include sagging skin, wrinkles, and dark marks. There also may be an increased risk of getting skin cancer. This is why sunscreen should be applied to all skin that does not require UVB phototherapy and a dermatologist must closely monitor all patients who receive phototherapy.

Lebwohl M, Ali S. “Treatment of psoriasis. Part 1. Topical therapy and phototherapy.” Journal of the American Academy of Dermatology October 2001; 45: 487-98; quiz 99-502.

Menter A, Korman NJ, Elmets CA et al. “Guidelines of care for the management of psoriasis and psoriatic arthritis: Section 5. Guidelines of care for the treatment of psoriasis with phototherapy and photochemotherapy.” Journal of the American Academy of Dermatology January 2010; 62: 114-35.

Zanolli  MD, Feldman SR, Clark AR, et al. 2000. “Phototherapy Treatment Protocols.” New York, NY: Parthenon Publishing Group.  

All content solely developed by the American Academy of Dermatology


For an overview, visit the AAD pamphlet Psoriasis and Psoriatic Arthritis.




What Dermatologists Tell Their Patients

For severe or stubborn psoriasis, combining UVB phototherapy with another psoriasis treatment often means faster clearing and fewer side effects.





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