The protective effect of a sunscreen filter chemically induced in normal skin was tested by using direct sunlight exposure to assure effectiveness. The topical preparation was applied immediately after mixing. Washing with soap and water did not remove the protective filter. Greater protection resulted from repetitive use or increase of the applied quantity, or both. Separate application of either component of the mixture produced no significant protection in clinical trials and in vitro experiments.
FUSARO RM, RUNGE WJ, LYNCH FW, WATSON ACJ. Sunlight Protection in Normal SkinBy Absorptive Filter Chemically Induced in Stratum Corneum. Arch Dermatol. 1966;93(1):106–111. doi:10.1001/archderm.1966.01600190112025
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