NEW EVALUATION TECHNIQUES FOR SUNSCREENS ,591 IN VITRO STUDIES WITH HUMAN EPIDERMIS Specimens of Caucasian human skin were surgically obtained at autopsy, and the intact epidermis was separated from the underlying tissues by the stretch technique (9). Histological examination of the epidermal skin revealed good, white, entire epidermis, with a total thick- ness of 40 /•, comprised of stratum corneum (16 /• thick), and stratum malphighian (24/• thick). The epidermal section was then mounted on a quartz slide for total transmission and reflection measurements. The same measurements were repeated after the physical/chemical sunscreen was applied to the epidermis. The total transmission of the epidermal 100 •) 7o 20 I0 ................ - .-i 11 -- ! i 250 300 350 400 WAVELENGTH rnp Figure 9. Total transmission of human epidermis (in vitro) using spectrophotometer with integrating spheres. ---- human epidermis and - - - human epidermis with sunscreen product, 5% amyl-p-dimethylaminobenzoate d- 10% talc in an opaque cream base, applied specimen was similar to that found by Everett et al. (10) using a similar technique of measurement. The application of the chemical/physical sunscreen to the epidermis considerably reduced the total transmission of both ultraviolet and visible light to less than 3% of the light pene- trating the epidermis originally (Fig. 9). In the regions where the skin normally transmitted the greatest amount of light (320-700 m/•) the physical sunscreen component (talc) of the combination sunscreen product lowered the total transmission markedly. In the sunburn re- gion (280-320 m/•) the total transmission was also markedly reduced because of the chemical sunscreen component.

592 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS A considerable quantity of the light in the sunburn and solar carcino- genic portion of the spectrum penetrates through normal epidermal layers to the dermis. The application of the sunscreen markedly re- duces this penetration. The reduction in transmittance corresponds somewhat roughly to the observed erythemal protection obtained with this chemical/physical sunscreen product. The initial reflection spectra obtained from. these epidermal skin specimens (Fig. 10) were characteristic of those observed for other specimens by Everett et al. (10). The addition of a chemical/physical 100 ÷ 9O 80 7O 60 50, 40 = 30= 20= 10. I i i 250 330 350 403 WAVELENGTH Figure 10. Percent reflection of human epidermis (in vitro) using spectrophotometer with integrating spheres. -- human epidermis and ..... human epidermis with sunscreen product, 5% amyl-p-dimethylaminobenzoate -4- 10% talc in an opaque cream base, applied sunscreen product altered the reflection spectra in the sunburn region only a little. In the visible (370-700 m/•), the addition of the sunscreen markedly increased reflection to one and one-half times normal reflect- ance. In the region where the chemical sunscreen of the product as well as the skin absorbed the strongest (280-350 m/•) the skin and sunscreen combination reflected less light than was reflected by the skin initially. Throughout the shorter portion of the spectrum (230-280 m/•) the skin alone and skin with sunscreen reflected the same. IN glvo REFLECTION STUDIES WITH HUMAN SKIN Based on the in vitro studies, in vivo studies were attempted, using the dorsal surface skin of subject's hand in place of the epidermis speci- men. Three in vivo studies indicate very little difference between the