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IN VITRO PERCUTANEOUS ABSORPTION OF ACRYLAMIDE AND STYRENE FROM COSMETIC VEHICLES THROUGH FUZZY RAT AND HUMAN SKIN

ABSTRACT Acrylamide (ACR) and styrene (STY) are residual monomers that remain as impurities in polymers used in hair, nail, and skin care products. These residual monomers may be substantially absorbed through skin. Acrylamide is known to be a neurotoxin in humans and a carcinogen in animals, while styrene has been reported to cause neurotoxic effects in humans and animals and carcinogenic effects in rodents. Therefore, studies were conducted to measure the extent of ACR and STY absorption in fuzzy rat and human skin relevant to exposures from personal care products using in vitro diffusion cell techniques. [14C]-ACR was applied to skin in flow through diffusion cells for 24 h using an oil-in-water (O/W) emulsion at doses of 2.2 and 13.3 μg/cm2 (fuzzy rat skin) and 0.2, 2.2, and 13.3 μg/cm2 (human skin). [14C]-ACR was also applied to human skin using a 2% polyacrylamide gel cream at a dose of 0.3 μg/cm2. [14C]-STY was applied to fuzzy rat and human skin using the O/W emulsion at a dose of 4.1 μg/cm2. The total amount of ACR or STY that penetrated into skin layers and receptor fluid at the end of the 24 h experiment was measured and expressed as the percent of applied dose penetrated. Absorption was defined as the amount of ACR or STY absorbed into the receptor fluid. At the both the 2.2 and 13.3 μg/cm2 dose levels using the O/W emulsion, ACR was rapidly absorbed through both fuzzy rat and human skin, with peak absorption occurring at 6 h. For fuzzy rat skin, total ACR penetrated was 52.9±1.3% at the lower dose level and 49.7±2.4% at the higher dose level. For human skin, total ACR penetrated was very similar with and 48.9±1.4% (0.2 μg/cm2 dose level), 49.5±4.4% (2.2 μg/cm2 dose level), and 60.6±12.1% (13.3 μg/cm2 dose level). The total ACR penetrated was reduced to 38.7±11.9% when ACR was applied using the 2% polyacrylamide gel cream (0.3 μg/cm2 dose level). The amounts of total STY that penetrated into fuzzy rat and human skin using the O/W emulsion vehicle were identical at 1.3% (4.1 μg/cm2 dose level). Although absorption of STY was relatively low, it was nevertheless rapid with peak absorption occurring at 6 h. Approximately 84–92% of the total ACR or STY penetrated was absorbed into the receptor fluid while only 8–16% of the total ACR or STY penetrated remained in the skin at 24 h. For these monomers, rodent skin satisfactorily simulated the barrier properties of human skin; there was no significant difference in ACR and STY absorption between fuzzy rat and human skin.