A STUDY OF THE EFFECT OF ANATOMICAL SITE ON SUN PROTECTION FACTOR EFFICIENCY USING A NOVEL UV DELIVERY DEVICE

The design and performance of an instrument used to determine sun prot ection factor (SPF) efficiency anywhere on the body are discussed, The instrument, MICRO-SPF, delivered ultraviolet light (UV) to much small er skin surface areas (similar to 1.5 mm diameter) than those (greater than or equal to 10 mm diameter) irradiated by conventional UV delive ry systems (i.e., stand-alone solar UV simulators). The MICRO-SPF is a microprocessor-controlled fiber optic delivery system that can be opt ically interfaced to most solar UV simulator housings. Electromechanic al shutters were microprocessor-cont-rolled synchronously to allow all five elements of a geometric dose series to be administered simultane ously. SPF efficiency produced using the MICRO-SPF was compared with S PF efficiency produced using a conventional solar UV simulator. No sta tistically significant difference was observed between SPFs produced u sing the MICRO-SPF and SPFs produced using the conventional solar UV s imulator for an estimated SPF 4 product and an estimated SPF 15 produc t. The effect of anatomical site on UV exposure time for minimal perce ptible erythema (MPE) and on SPF efficiency was examined using the MIC RO-SPF on the cheek, back, volar forearm, and outer calf. Exposure tim e for MPE for each anatomical site was statistically significant (p < 0.0001) from ail other anatomical sites; average exposure rimes for MP E were 29.4 sec for back, 33.8 sec for face, 47.8 sec for volar forear m, and 61.8 sec for outer calf. Despite differences in natural photopr otection found for anatomical sites studied, no statistically signific ant difference was observed for comparison of SPF efficiency between a natomical sires. These results provide evidence that although signific ant physiological differences exist in skin as a function of anatomica l sire, sunscreen film formation and, therefore, sunscreen efficiency for the products tested may be unaffected by these differences.