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 dithranol 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 session.
- UVA light used with psoralen drugs is called PUVA. With PUVA, the treatment time is greatly reduced, from 20 minutes to about 2 minutes.
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 or take it by mouth. 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 therapies are:
- 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 dithranol, tar products, and UVB phototherapy.
- The Goeckerman 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 cancer.
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 worked.
UVB light alone (without drugs) is used for widespread plaque psoriasis and guttate psoriasis.
How Well It Works
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 plaque.
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 non-melanoma skin cancer. And phototherapy isn't recommended in people who have a history of skin cancer.
- Skin damage. 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 UVB.
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.
For people who have erythroderma or pustular psoriasis, UV treatment may make the condition worse.
- 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.
Current as of: October 31, 2019