FILM PROPERTIES OF POLYMERS USED IN ANHYDROUS SUNSCREEN FORMULATIONS 207 formed signifi cantly less permeable fi lms than Formulation C, which did not contain any polymer. Cumulative evaporimeter data indicated that the sunscreen phase had the high- est reduction in cumulative evaporation rate, specifi cally 39.3%/h, followed by the addi- tion of a fi lm former to the spray which reached an additional reduction of 17.9%/h in the best case. These fi ndings are quite reasonable, as sunscreen fi lter concentrations are typically much higher (typically 20–30% w/w) than polymer concentrations (typically 1–3% w/w) in the fi nal formulation. The data from the evaporimeter studies confi rmed that the sunscreen fi lters play a more important role in water vapor transmission than the polymers added to the formulation. This fi nding seems to correlate with previously presented data (6). It is also important to note that the addition of polymers to the sunscreen formulations increased its in vitro water resistance. MICROSCOPIC EVALUATION OF FILMS ON SKIN To better understand the deposition characteristics of the sunscreen systems on skin, we used SEM to carefully monitor the deposition behavior of sunscreen fi lms and to elucidate the architectural role played by several polymeric systems in the sunscreens. Figures 2 and 3 contain micrographs of corneocytes treated with all of the studied formulations at ×300 (Figure 2) and ×500 or ×1,000 (Figure 3) magnifi cations, respectively. Figure 1. Evaporation data obtained from sunscreen fi lms applied to ex vivo porcine skin in a Franz diffusion cell apparatus.

JOURNAL OF COSMETIC SCIENCE 208 Observation of the behavior of Formulation A demonstrated that this system did not leave any noticeable residue on the stratum corneum. The corneocytes appear very dis- tinct and no apparent fi lm was deposited on its surface. Such results are expected as For- mulation A contains about 93% (w/w) alcohol, which most likely evaporated before obtaining the micrographs. On the other hand, for Formulation B, which contained the polymeric fi lm former VA/butyl maleate/isobornyl acrylate copolymer at a level of 1% (w/w), we observed that the polymer formed a network over the stratum corneum. The network appeared a bit darker in the image than the corneocyte background. One interesting aspect of this fi lm former is its ability to form a clear, interconnected network over the stratum corneum as opposed to a distinct spray particle deposited on the surface. F igure 2. SEM micrographs of various sun care formulations deposited (sprayed) onto layers of stratum corne- um cells (magnifi cation = ×300). (A) Formulation A, (B) Formulation B, (C) Formulation C, (D) Formulation D, (E) Formulation E, and (F) Formulation F.