Drawbacks

Exposure to natural UV radiation is associated in humans with photoageing and skin cancer. In a 25-year follow up of 1738 Danish patients with psoriasis treated by heliotherapy at the Dead

Sea during 1972-73, the risks of basal cell and squamous cell carcinoma of the skin were 4-2 and 10-7 times higher, respectively, than expected in the general population.29 The authors point out that such patients will have had many other exposures to UV radiation but the risk from exposure to sunlight is clearly increased. There is, however, little evidence to suggest that therapeutic BBUVB irradiation for psoriasis conveys a significantly increased risk of developing skin cancer. There is as yet little evidence as to whether NBUVB is more or less harmful than BBUVB.33 The main risks of PUVA therapy are photoageing (premature skin ageing) and skin cancer. In addition to the characteristic changes of photoageing (dry skin, wrinkles, elastosis), people who have received large doses of PUVA are prone to developing widespread irregular dark freckling (PUVA lentigines) which may be cosmetically disfiguring and may be difficult to differentiate from early malignant melanoma. Skin cancer is a well-recognised effect of long-term PUVA therapy. In a meta-analysis of nine patient series including data on 12 142 people treated with PUVA followed up for between 5-13 years, a dose-dependent increase in incidence of squamous cell carcinoma was found, with a 14-fold increase in risk in recipients of >200 treatments or >2000 J/cm2 (CI 8-3 to 24-1); on the other hand there was little evidence that people who had received <100 treatments or <1000 J/cm2 were at significantly increased risk compared with the normal population.30 Risk of squamous cell carcinoma was increased in people with fairer skin types (types I and II). A combined analysis of two cohort studies of bath PUVA (n = 944) excluded a threefold excess risk of squamous cell carcinoma after a mean follow up of 14-7 years, suggesting that bath PUVA is possibly safer than oral PUVA.28 The risks of developing basal cell carcinoma do not appear to be substantially increased except in patients exposed to very high cumulative doses of UVA.58 A fourfold increase in the incidence of malignant melanoma has been found after long-term (15 years or more) follow up of people exposed to at least 200 PUVA treatments compared with those exposed to fewer (n = 1380, CI 2-0 to 9-2).31

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