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March 1991

Efficiency of Opaque Photoprotective Agents in the Visible Light Range

Author Affiliations

From the Departments of Dermatology, Wellman Laboratories of Photomedicine and Massachusetts General Hospital, The Beth Israel Hospital, Boston, Mass. Dr Levin is now in private practice in Atlanta, Ga.

Arch Dermatol. 1991;127(3):351-355. doi:10.1001/archderm.1991.01680030071009

• "Opaque" physical sunscreens are important for photoprotection of individuals with visible light and UV-A photosensitivity such as those with porphyria, drug photoallergy, and polymorphous light eruption. Diffuse spectral transmittance of various thicknesses of opaque sunscreen formulations were measured from 350- to 800-nm range using a spectrophotometer equipped with an integrating sphere. Transmission through 20% zinc oxide paste was high and decreased minimally despite large increases in the sunscreen layer thickness. Adding a visible light absorber such as iron oxide to scattering sunscreens, however, substantially lowered transmittance below that predicted by the product of the transmittances for each component alone. Opaque sunscreens protected against hematoporphyrin derivative photosensitization of albino guinea pig skin; these results were quantitatively consistent with the in vitro findings. Poor photoprotection against visible light is obtained with white paste sunscreens, even if thick layers are applied. The addition of pigments to such sunscreens, however, greatly enhances photoprotection and cosmetic acceptability.

(Arch Dermatol. 1991;127:351-355)

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