Two types of ultraviolet light are used in phototherapy, ultraviolet light A (UVA) and ultraviolet light B (UVB). UVB waves penetrate the skin and decrease the abnormally rapid growth of skin cells associated with psoriasis. Phototherapy with UVB involves exposing the skin to an artificial UVB light source for a controlled length of time. UVB treatments can be used alone or in combination with topical or oral medications.

During UVB treatment, psoriasis may worsen temporarily before improving. The skin may itch and become red because of exposure to UVB light. UVB is an established carcinogen (cancer-causing agent) in humans. However, there is no direct evidence of increased risk of skin cancer from UVB treatments for psoriasis. Your dermatologist may recommend the use of sunscreen on uninvolved skin as a way to minimize UVB exposure.

Ultraviolet light A (UVA) is normally used in conjunction with psoralen (a light-sensitizing medication which can be taken orally or topically). This is referred to as PUVA. PUVA also works to slow down the excessive cell reproduction of psoriasis and can clear the symptoms for varying periods of time. It is also used to treat severe, disabling psoriasis that cannot be controlled by systemic drugs. Studies show that PUVA clears psoriasis for more than 85 percent who use it and that it induces long remission times, even without maintenance therapy.

The most common short-term side effects of oral PUVA are nausea, itching and redness of the skin. Topical PUVA avoids some of the short-term side effects of oral PUVA. However it is more labor intensive and poses a greater risk of sunburn from the PUVA treatment. Long-term side effects for PUVA treatment are skin cancer, freckling/premature aging of the skins or cataracts.

The chief long-term risk of PUVA therapy is a higher risk of skin cancer, particularly non-aggressive forms like squamous cell carcinoma (SCC) and basal cell carcinoma (BCC). Studies have shown that the more treatments you have, the more at risk you are for developing these types of skin cancers. It is recommended that any patient who has had more than 150 PUVA treatments have an annual skin exam by a dermatologist. When skin cancer is detected early it is almost always easily treated.

Patients who have had high numbers of PUVA treatments are also at risk for freckling and abnormal aging of the skin. This can take the form of wrinkles, dryness, or tight, shiny skin. Discolored spots that look like freckles may develop.

Psoralen remains in the lens of the eye for a period of time after ingestion. It is important to protect your eyes for 12 to 24 hours after taking psoralen to prevent cataract formation. To date, no increase in cataracts has been noted in patients using proper eye protection.

Treatment with ultraviolet light is a very effective therapy for psoriasis, especially when topical treatments cannot be used. The key to success with phototherapy is consistency. It is also important that patients understand the potential risks. Side effects can be minimized, however, by carefully following safety precautions and rotating therapies.