Per- and polyfluoroalkyl substances (PFAS) often make headlines as health agencies worldwide work to regulate their use. While most restrictions focus on PFAS in drinking water, the primary exposure pathway, scientists are increasingly investigating alternative routes, such as dermal absorption from cosmetics, sunscreens, and other everyday products.
Per- and polyfluoroalkyl substances (PFAS) are a vast group of thousands of synthetic compounds characterized by their fluorinated alkyl chains. Notorious for their resistance to water, oil, and heat, PFAS have been extensively utilized in various industrial and consumer products, such as clothing, food packaging, cookware, and smartwatch bands (1). However, their environmental persistence and potential health risks have raised significant concerns among scientists and regulatory bodies.
Woman applying body cream on arm, beauty skin care concept, studio shot: © triocean - stock.adobe.com
One of the primary challenges in PFAS analysis is the ubiquitous presence of these compounds; it is believed that they are in the bloodstream of almost every person on the planet. The potential for contamination and interference can therefore not be underestimated. Laboratory equipment, consumables, and even personal care products used by analysts can introduce background PFAS, complicating accurate quantification. Rigorous quality control measures, such as using PFAS-free materials, is essential to mitigate these interferences. In addition, robust sample preparation protocols, such as solid-phase extraction (SPE) and matrix clean-up steps, can help to enhance method reliability.
The U.S. and the European Union (EU) are leading the charge when it comes to regulating PFAS. In April 2024, the U.S. Environmental Protection Agency (EPA) established the first-ever national, legally enforceable drinking water standards for six PFAS compounds: perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), perfluorononanoic acid (PFNA), perfluorohexanesulphonic acid (PFHxS), perfluorobutanesulfonic acid (PFBS), and GenX chemicals (2). Public water systems are required to monitor and reduce these PFAS levels to near-zero within three years, with an aim to protect approximately 100 million people from exposure. The EU is also focused on regulating PFAS through Regulation (EC) No 850/2004 (known as the “POP Regulation”) (3) and REACH (4), which came into force in 2007. The UK has been criticized in recent months for lagging behind Europe in its regulations.
While the EU is moving towards a group ban of non-essential uses of PFAS, the UK plans to regulate them in smaller groups, a risk-based approach at odds with the hazard-based approach favoured in Europe (5). Recent guidance issued by the Drinking Water Inspectorate (DWI) now requires water companies to enforce a cumulative list of 100 ng/l for a list of 48 PFAS (6). This guidance came into effect from January 2025. The regulatory framework for PFAS is evolving, with agencies like the EPA actively developing and updating methods for PFAS detection in various matrices. Continued collaboration between regulatory bodies and analytical laboratories are crucial to establish comprehensive guidelines that ensure consistency and comparability of data across studies.
Most regulations pertaining to PFAS focus on drinking water because ingestion is considered the primary route of exposure. But drinking water is not the only way that PFAS can enter the body, recent studies have found that PFAS can be found at high levels in common smartwatch and fitness bands (1), raising concerns about dermal exposure to these persistent chemicals. Professor Stuart Harrad from the University of Birmingham has been investigating how PFAS are absorbed through the skin using both liquid chromatography tandem mass spectrometry (LC–MS/MS) and gas chromatography–electron capture detection (GC–ECD).
“The dermal uptake of PFAS (and related compounds such as halogenated flame retardants) is essentially a two-step process. First, PFAS transfer from the source material—such as dust, fabrics, or cosmetics—to skin surface fluids, sweat, and sebum,” he told LCGC International in an interview. “This transfer is known as bioaccessibility. Once PFAS are in the skin fluids, they become available for potential transfer across the skin barrier into the bloodstream. The percentage of PFAS present in skin fluids that transfer into the bloodstream is referred to as the bioavailability. This process is influenced by kinetic factors, as the transfer from skin fluids across the skin barrier does not occur instantaneously. At the end of our experiments, we observed different percentages of PFAS distributed across: (a) the skin fluids (unabsorbed), (b) the skin itself (which if the experiments continued for a longer time, could potentially pass through into the bloodstream), and (c) the bloodstream (absorbed) (7).”
A study published in the journal Environment International was conducted using a human volunteer who applied a known dose of isotopically labeled PFOA mixed into sunscreen (8). “The peak concentration in the bloodstream occurred approximately three weeks after sunscreen application,” Harrad noted.
Harrad’s own research highlights the impact of the type of PFAS on absorption. Using in vitro 3D human skin equivalent models, his team had investigated the dermal permeation of 17 PFAS chemicals and found that, rather than acting as a barrier, the skin was able to absorb these compounds (9).
“We found an inverse correlation between LogKOW and the absorbed fraction, meaning shorter-chain PFAS were absorbed into the bloodstream more efficiently over 24 h compared to longer-chain PFAS. However, a significant proportion of longer-chain PFAS (for example, 68% for perfluorononanesulfonic acid [PFNS C9]) remained in the skin tissue, indicating they may eventually be absorbed but require more time. Another important influence is the composition of the skin surface fluids. Longer chain compounds are more bioaccessible in skin fluid with more sebum than sweat and vice versa,” Harrad explained.
Harrad shared the following insight when it comes to the potential long-term effects of chronic low-level dermal exposure to PFAS. Some PFAS raise major health concerns, including carcinogenicity—PFOA is classified as a known human carcinogen by the IARC. In addition, reduced immune responses to childhood vaccines such as diphtheria have been linked to PFOA, PFOS, PFHxS, and PFNA, prompting the European Food Safety Authority (EFSA) to set a tolerable weekly intake for these four PFAS at 4.4 ng/kg body weight/day.
Regulations specifically targeting dermal exposure to PFAS are relatively limited compared to those addressing ingestion. There are however references to skin exposure within broader guidelines. For example, under REACH, PFAS substances may be restricted or require specific risk assessments, including dermal exposure. For example, textiles, leather, and coated materials containing PFAS that come into direct contact with the skin are being closely examined. Ingredients in cosmetics in both the US and UK are monitored for their safety. The Modernization of Cosmetics Regulation Act of 2022 (MoCRA) will assess the safety of PFAS over time and requires FDA to publish a report on their findings. This will lay the groundwork for any future update to guidance and regulations.
The field of PFAS research is rapidly advancing and evolving, with chromatographic techniques playing a pivotal role in addressing these analytical challenges. Continuous method refinement, coupled with a proactive approach to contamination control and standardization, will enhance the accuracy and reliability of PFAS analysis, supporting environmental monitoring and helping to protect the public.
(1) Wicks, A.; Whitehead, H. D.; Peaslee G. F. Presence of Perfluorohexanoic Acid in Fluoroelastomer Watch Bands. Environ. Sci. Technol. Lett. 2024, 12 (1), 25–30. DOI: 10.1021/acs.estlett.4c00907
(2) US EPA, Per- and Polyfluoroalkyl Substances (PFAS) Final PFAS National Primary Drinking Water Regulation. https://www.epa.gov/sdwa/and-polyfluoroalkyl-substances-pfas (accessed-2025-01-21).
(3) EUR-Lex, Regulation (EC) No 850/2004 of the European Parliament and of the Council of 29 April 2004 on persistent organic pollutants and amending Directive 79/117/EEC. https://eur-lex.europa.eu/eli/reg/2004/850/oj(accessed-2025-01-21).
(4) European Commission, REACH Regulation. https://environment.ec.europa.eu/topics/chemicals/reach-regulation_en (accessed-2025-01-21).
(5) UK Failing to Match EU in Fight Against ‘Forever Chemicals’, Say Scientists. The Guardian, https://www.theguardian.com/environment/2025/jan/17/uk-failing-to-match-eu-in-fight-against-forever-chemicals-say-scientists (accessed-2025-01-21).
(6) Drinking Water Inspectorate, Guidance on the Water Supply (Water Quality) Regulations 2016 (as amended) for England and Water Supply (Water Quality) Regulations 2018 for Wales Specific to PFAS (per- and polyfluoroalkyl substances) in Drinking Water. https://dwi-production-files.s3.eu-west-2.amazonaws.com/wp-content/uploads/2024/08/22155613/DWI_PFAS-Guidance_Aug-2024_FINAL-2.pdf (accessed-2025-01-21).
(7) Namazkar, S.; Ragnarsdottir, O.; Josefsson, A.; et al. Characterization and Dermal Bioaccessibility of Residual- and Listed PFAS Ingredients in Cosmetic Products. Environ. Sci. Technol. Lett. 2024, 26 (2), 259–268. DOI: 10.1039/D3EM00461A
(8) Abraham, K.; Monien, B. H.; Transdermal Absorption of 13C4-Perfluorooctanoic Acid (13C4-PFOA) From a Sunscreen in a Male Volunteer – What Could be the Contribution of Cosmetics to the Internal Exposure of Perfluoroalkyl Substances (PFAS)? Environ. Int. 2022, 169, 107549. DOI: 10.1016/j.envint.2022.107549
(9) Ragnarsdottir, O.; Abou-Elwafa Abdallah, M.; Harrad, S. Dermal Bioavailability of Perfluoroalkyl Substances Using In Vitro 3D Human Skin Equivalent Models. Environ. Int. 2024, 188, 108771. DOI: 10.1016/j.envint.2024.108772