Photoprotective action of emollients in ultraviolet therapy of psoriasis.

An in vitro technique was used to measure the monochromatic protection factors of all emollients available on prescription. The action spectra for ultraviolet erythema and erythema in psoralen-sensitized skin were used to calculate, for each emollient, erythema protection factors relevant to UVB phototherapy and psoralen photochemotherapy, respectively. Of the 40 products tested, 22 (55%) had a UVB erythema protection factor > 1.2 at an application density of 2 microliters/cm2, and 31 (78%) at an application density of 4 microliters/cm2. Fewer products, 25% at 2 microliters/cm2 and 50% at 4 microliters/cm2, had a psoralen erythema protection factor > 1.2. A protection factor of 1.2 is equivalent to a reduction in ultraviolet dose of 17%, and is thus likely to be of clinical importance. These results allow a choice of emollient products which may improve response by increasing transmission of radiation through psoriasis scale without a concomitant decrease in transmission due to a sunscreening action.