Phototherapy involves the use of light to treat a medical condition. Ultraviolet light therapy improves psoriasis symptoms in some people. Phototherapy may only use ultraviolet light, or may combine the use of ultraviolet light with psoralen, a drug that increases light sensitivity. While ultraviolet rays occur naturally in sunlight, excessive sun exposure causes sunburn, which can make symptoms worsen. Phototherapy uses carefully measured amounts of ultraviolet light; a safety measure that cannot be duplicated by simple exposure to the sun. A side effect of this is photo damage or increased risk of skin cancers.
Natural sunlight contains ultraviolet (UV) light. UV light kills T cells in skin, reducing redness and slowing the overproduction of skin cells that causes scaling. This is why brief, regular periods of sun exposure can help to clear psoriasis. Exposing the skin to UV light in carefully controlled doses is called phototherapy. Sunlight contains two kinds of UV light, known as UVA and UVB. Both can be used to treat psoriasis. In phototherapy, the affected person sits or lies inside a "light box," a booth fitted with special light-emitting tubes. Usually, people go to a doctor's office to receive phototherapy. Sometimes a light box can be purchased with a doctor's prescription for use at home.
UVB therapy: Treatment with UVB light is the safest form of phototherapy for widespread psoriasis or psoriasis that has not responded to medications applied to the skin. Usually 3 to 5 treatments a week are recommended, with a gradual increase in UV exposure depending on skin type. Significant clearing of psoriasis can be expected in 1 to 3 months. Exposure to UVB light must be carefully monitored to prevent sunburn. During treatment, the eyes must be shielded with goggles to guard against the possible formation of cataracts. Skin aging may be a side effect of UVB treatment. Large long-term studies have found no evidence of an increase in the risk of skin cancer as a result of UVB treatment. UVB phototherapy may be combined with tar, anthralin, topical steroids, or other medications applied to the skin. The Goeckerman regimen, developed at the Mayo Clinic, uses crude coal tar, tar baths, and UVB treatment to treat widespread psoriasis. The Ingram regimen uses coal tar baths, anthralin paste, and UVB therapy.
PUVA: This treatment combines a medication called psoralen with exposure to UVA light. (PUVA stands for Psoralen with UVA.) Psoralen may be taken by mouth or applied to the skin. It makes the skin more sensitive to light. Treatment is given 2 or 3 times a week, with a gradual increase in UV exposure depending on skin type. As with UVB therapy, significant clearing of psoriasis can be expected in 1 to 3 months. Compared with UVB therapy, PUVA clears skin more consistently with fewer treatments. However, PUVA has more short-term side effects, such as nausea, headache, fatigue, burning, and itching. When psoralen is taken by mouth, nausea may be avoided by taking food at the same time. As with UVB therapy, the eyes must be shielded with goggles during UVA exposure to guard against the formation of cataracts. Psoralen can be applied to the skin in the form of a cream, lotion, gel, or solution. After the paint, soak, or bath routine, the person is exposed to UVA light in a light box. UVA light is the same kind used in commercial tanning salons. Treating psoriasis in tanning salons is not recommended because attendants are untrained and the dose of UVA is not controlled. UVA therapy must be given in carefully controlled doses and supervised by a doctor. PUVA is recommended for people with moderate to severe psoriasis or who have not improved with other treatments. Long-term use of PUVA increases the risk of developing certain types of skin cancer. Regular medical examinations are advised to check for signs of skin cancer.
