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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:
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
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 therapies are:
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.
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.
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.
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:
UVA produces fewer and milder short-term side effects than UVB.
CitationsGudjonsson 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: March 3, 2021
Author: Healthwise Staff
Medical Review:Adam Husney MD - Family Medicine & E. Gregory Thompson MD - Internal Medicine & Martin J. Gabica MD - Family Medicine & Amy McMichael MD - Dermatology
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