Modulation of ultraviolet (UV) transmission by emollients: relevance to narrowband UVB phototherapy and psoralen plus UVA photochemotherapy

Abstract

Patients with psoriasis undergoing or about to undergo ultraviolet (UV) phototherapy and photochemotherapy often have thick scale on their plaques which can prevent the penetration of UV radiation. Emollients are used to moisturize the skin and to prevent or reduce some of the milder side-effects ('dryness', itching) sometimes experienced during UV therapy. However, emollients can alter the UV transmission of skin and thus may alter the clinical effects of phototherapy and photochemotherapy. We tested 30 of the topical emollients in the British National Formulary (BNF) using a standard in vitro technique used to test sunscreens. We also surveyed U.K. phototherapy units to establish routine practice for emollient use in phototherapy and photochemotherapy. We used a standard in vitro technique to measure the monochromatic protection factors (MPFs) of 30 non-bath emollients from the BNF. An application rate of 2 mg cm-2 was used. For the assessment of effects during narrowband UVB (TL-01) phototherapy, the mean of the protection factors at 310 and 315 nm was calculated; for psoralen plus UVA photochemotherapy the mean UVA protection factor was used. A questionnaire survey was used to assess routine practice concerning emollient use prior to phototherapies in phototherapy units throughout the U.K. In the UVA range, 17 of the 30 emollients gave protection factors of 1.2 or above. In the UVB range, 23 of 30 had an MPF of 1.2 or above. Yellow soft paraffin had the highest protection factor in the UVB range. Of 78 centres surveyed, 57 returned completed questionnaires (73%). Seventeen of 57 (30%) centres routinely used emollients immediately prior to administering phototherapy treatments. The remaining 40 of 57 (70%) did not. Forty-five (79%) responding centres recommended the use of emollients after phototherapy. This study has revealed considerable variability in the practice of emollient use before phototherapy treatments. Although the majority of centres included in this study did not routinely use emollients, almost one third did. Our in vitro measurement of 30 emollients revealed marked variation in UV transmission, with many emollients blocking sufficient UV to affect the response to therapy.