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
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
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
Lebwohl M, Ali S.
“Treatment of psoriasis. Part 1. Topical therapy and
phototherapy,” 487-98; quiz 99-502. Copyright Elsevier
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
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
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
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;
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.
Dermatologists Tell Their Patients
For severe or stubborn
psoriasis, combining UVB phototherapy with another
psoriasis treatment often means faster clearing and
fewer side effects.