Phototherapy is the use of ultraviolet (UV) light to slow the rapid
growth of new skin cells. This is helpful in treating psoriasis, which causes skin cells to grow too
rapidly. There are two types of ultraviolet (UV) light therapy:
Ultraviolet B (UVB)
Exposure times start at 30 to 60 seconds when therapy begins. You are exposed to the light until it causes the skin to turn slightly pink. When the skin no longer turns pink in the 24 hours after a treatment, the exposure time is increased.
Treatments are given several times a
week until the psoriasis clears up.
UVB light is used alone, with tar products (Goeckerman
treatment), or with anthralin applied to the skin (Ingram regimen).
One phototherapy option includes the use of narrow-band UVB light.
This exposes you to only the wavelengths of light that work for
treating psoriasis. Broadband UVB therapy uses a wider range of wavelengths.
A laser treatment for psoriasis (excimer laser) also uses UVB light. Excimer laser works well for psoriasis that has been hard to treat on the elbows and knees.footnote 1
Ultraviolet A (UVA)
UVA penetrates deeper into the skin than UVB.
Treatment with UVA typically takes 20 minutes for a
UVA light used with psoralen drugs is called PUVA. With
PUVA, the treatment time is greatly reduced, from 20 minutes to about 2
Treatments with UVB and UVA
Phototherapy can be used alone or with medicines. UVB light
therapy is used alone to treat severe psoriasis. Typically, when medicines for
psoriasis are used with light therapy, you will use or take the medicine first.
You may apply it to your skin, take it by mouth, or use it as bath salts in
water. Then you will go into a booth and be exposed to the UV light. Using two
kinds of treatment is called combination therapy. Three common combination
Psoralen and UVA light therapy (PUVA),
which combines UVA exposure and a medicine (called a psoralen) that makes your
skin more sensitive to light.
The Ingram regimen, which combines
tar products, and UVB phototherapy.
treatment, a combination of
tar products and UVB phototherapy.
Your body is exposed to UV light from banks of light tubes that
give off either UVB or UVA light in a booth. Booths come in several
designs. Some look like phone booths and you can stand in them. Others look
like tanning beds and you can lie down during treatment. The booth will
record the total amount of light you are exposed to.
In general, your entire body is exposed to the light. (If psoriasis
affects only certain areas of your body, UV light may be directed at these
selected areas only.) You will wear sunglasses that block UV light and goggles
or a blindfold to protect your eyes from getting cataracts. Men may also
need to shield their genitals to protect them from an increased risk of genital
What To Expect After Treatment
As your skin recovers from treatment, it should be checked at least
once or twice a year for signs of skin damage or skin cancer.
Why It Is Done
PUVA (the use of psoralen medicines with UVA light therapy) is
usually used when psoriasis is disabling and safer treatments have not
Phototherapy is usually an effective treatment for
psoriasis.footnote 2 Partial to full skin clearing occurs after
an average of 20 clinic treatments. More severe psoriasis may require more
treatments. Using home equipment, which is less powerful than equipment at a
clinic, takes 40 to 60 sessions to clear the skin.
Doses of UVB high enough to cause the skin to turn red, used with
petroleum jelly (such as Vaseline) or other moisturizers, can clear psoriasis
When using UVA alone, treatments may be helpful but take much
longer to clear psoriasis. UVA is very effective when used with a
photosensitizing drug (psoralen). This combination treatment is called PUVA.
Risks of phototherapy include:
Skin cancer. PUVA increases a person’s risk for both melanoma and nonmelanoma skin cancer. And phototherapy isn’t recommended for people who have a history of skin cancer.
Long-term exposure to UVA light may lead to skin damage, aging, skin cancer,
and cataracts. This risk of cataracts can be reduced by regular use of
sunglasses that block UVA light when you are outdoors.
Cancer. The male
genitals are highly susceptible to the cancer-causing effects of both PUVA
therapy and UVB therapy.
UVA produces fewer and milder short-term side effects than
What To Think About
Phototherapy requires a lot of time for treatment, and UV booth
equipment is expensive. Commercial tanning beds, which emit UVA, are less
effective for psoriasis than UV booths.
The National Psoriasis Foundation provides information on
where you can buy home light
therapy equipment. Home light therapy should only be done under your doctor’s
supervision. For more information, see the organization’s website at
Gudjonsson JE, Elder JT (2012). Psoriasis. In LA Goldman et al., eds., Fitzpatrick’s Dermatology in General Medicine, 8th ed., vol. 1, pp. 197-231. New York: McGraw-Hill.
Habif TP, et al. (2011). Psoriasis and other papulosquamous diseases. In Skin Disease: Diagnosis and Treatment, 3rd ed., pp. 120-153. Edinburgh: Saunders.
ByHealthwise Staff Primary Medical ReviewerAdam Husney, MD – Family Medicine E. Gregory Thompson, MD – Internal Medicine Martin J. Gabica, MD – Family Medicine Specialist Medical ReviewerAmy McMichael, MD – Dermatology