The impact of emollients on phototherapy: A review

When treating psoriasis, various topical emollients exist that can affect the penetration of ultraviolet radiationin phototherapy. Compared with normal-appearing skin with a reflectance of 4% to 5%, psoriatic skin hashigher reflectance as a result of its increased air-to-corneocyte interfaces. Studies have tested the effect ofemollients on light penetration by assessing psoriatic plaque clearance, differences in minimal erythemadose, and physical properties of the emollient (eg, monochromatic protection factor and absorbance). Psoriatic plaque clearance was found to improve with serous (thin liquid)-based emollients (eg, Vaseline oil[Unilever, Blackfriars, London, UK], mineral oil, and glycerol), whereas clearance decreased with salicylic acid and viscous-based emollients (eg, petrolatum). Emollients with high ultraviolet absorbance properties increased minimal erythema dose, and those with low absorbance properties decreased minimal erythema dose. Interestingly, when a liquid emollient with a refractive index close to that of normal appearing skin was applied, there was a net increase in light absorption, or a reduction in reflection that exceeded the emollient's innate ability to absorb light.