Which PFAS species have documented dermal absorption in 3D human skin models and what are their reported transfer rates?
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Executive summary
A 2024 in vitro study using 3D human skin equivalent models tested 17 PFAS and found dermal uptake for most compounds: 15 of the 17 showed at least 5% systemic absorption under the study conditions (exposure 500 ng/cm2 in methanol, 24–36 h) [1][2]. Short‑chain PFAS tended to penetrate more readily than long‑chain PFAS, with specific examples including perfluoropentanoic acid (PFPeA) and perfluorobutane sulfonate (PFBS) showing the highest absorbed fractions in that dataset [1].
1. The data headline: 15 of 17 PFAS showed measurable dermal absorption
The Environment International study reported that, under the experimental conditions used, 15 out of 17 tested PFAS produced “substantial” dermal absorption—defined in press summaries as at least about 5% of the applied dose—when applied to multilayer 3D human skin equivalents (500 ng/cm2 in methanol for 24–36 hours) [2][1]. Multiple press outlets and institutional releases reiterated that most tested PFAS crossed or were taken up by the skin model and that a sizeable fraction of the applied dose could be absorbed or remain within skin layers [3][4][5].
2. Which PFAS were documented to cross the skin and what transfer rates were reported
The peer‑reviewed paper and summaries give specific absorption fractions for several compounds: perfluoropentanoic acid (PFPeA) had the highest reported absorbed fraction at about 58.9%, and perfluorobutane sulfonate (PFBS) was reported at about 48.7% absorbed [1]. Perfluorooctanoic acid (PFOA), one of the most regulated PFAS, was reported to have an absorption into the “bloodstream” equivalent of 13.5% of the applied dose in the study’s experimental setup, with an additional ~38% of the applied dose retained in the skin tissue at the end of exposure [5][2]. The study also flagged FBSA (a short‑chain sulfonic species) as able to penetrate human skin in vitro [6].
3. Chemical patterns: chain length and physicochemical predictors of uptake
The study found a clear inverse relationship between carbon chain length and absorbed fraction for both perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs): absorbed fraction decreased as chain length increased, with strong correlations reported (r ≈ 0.97 for PFCAs and PFSAs, p-values ≈ 0.001–0.004) [1]. Physicochemical metrics such as logKOW also correlated inversely with dermal permeation, indicating more hydrophilic/shorter chain PFAS permeated the skin model more readily [1].
4. Experimental context and why numbers are not a direct real‑world exposure map
All absorption figures reported derive from a controlled in vitro protocol: a 500 ng/cm2 dose delivered in methanol for 24–36 hours to multilayered lab‑grown skin equivalents—not intact human volunteers or complex product matrices—so the absolute percentages reflect that specific setup [1][2]. The paper and commentators note the need for standardized conditions and caution in extrapolating to real consumer exposures, where vehicles, skin condition, repeated low doses, and product formulation will alter kinetics [6][7][8]. Independent human volunteer studies of PFOA show widely varying dermal kinetic estimates across different methods, underlining that dermal uptake estimates can span several orders of magnitude depending on design [8].
5. Implications, alternatives and open questions
The findings challenge the longstanding assumption that ionized PFAS cannot breach the skin barrier and raise plausibility that everyday contact with PFAS‑containing products could contribute to internal exposure, especially for short‑chain replacements; however, regulators and exposure scientists emphasize that dermal uptake relative to ingestion may still be lower for some PFAS and that more work is needed to quantify real‑world risk [9][8]. Study limitations—vehicle, dose, model system—mean the field still needs human volunteer data, product‑matrix studies, and standardized protocols before definitive exposure conversions can be made [6][7].