Toxic compounds found in synthetic and natural hair extensions

By Dr. Liji Thomas, MDReviewed by Lauren HardakerFeb 16 2026

A first-of-its-kind chemical analysis reveals that many widely used hair extensions contain hazard-listed substances, highlighting gaps in labeling and oversight while underscoring that the presence of chemicals does not necessarily mean proven health harm.

Study: Identifying Chemicals of Health Concern in Hair Extensions Using Suspect Screening and Nontargeted Analysis. Image credit: Vershinin89/Shutterstock.com

Hair extensions are a poorly regulated, largely uncharacterized category of cosmetic aids that potentially expose consumers to an unknown array of chemicals. A recent study in the journal Environment & Health analyzed 44 hair samples: 43 from commercially available products and one pooled, donated hair sample.

Global hair extension market grows amid oversight gaps

Hair extensions may consist of human hair or other fibers, natural or synthetic. These may be treated with multiple chemicals, such as fire retardants, waterproofing agents, pesticides, antimicrobials, and conditioners. The US is the largest importer, with global trade projected to exceed $14 billion by 2028.

Common hairstyling techniques release volatile organic chemicals (VOCs). Many hair care products contain metals and organic chemicals, some carcinogenic. Regulatory oversight has been limited for multiple reasons, including opaque labeling, inadequate data on exposure and toxicity, and a lack of strong data linking exposures to health outcomes when long latency periods are involved.

Consumer items and chemical exposure

Earlier studies by the Environmental Protection Agency (EPA) recognized chemical exposures associated with consumer product use. These chemicals may be linked to reproductive health effects, impaired fetal development, and increased cancer risk. Notable examples include formaldehyde in personal care products, polybrominated diphenyl ethers used as flame retardants in textiles and furnishings, and per- and polyfluoroalkyl substances (PFAS), which are used to provide water-repellent properties.

Despite this, few consumer products or the chemicals used in such products are comprehensively regulated by the US Food and Drug Administration or the EPA. State regulations, such as California’s Proposition 65, address part of this gap by mandating warning labels for products that expose consumers to hazardous chemicals, and they have been associated with safer product reformulations and lower chemical exposure.

Chemicals and hair extensions

Hair extensions are disproportionately used by Black women, with annual use reported at about 70%, compared with approximately 10% among White, Latina, and Vietnamese women. These products remain in close contact with the scalp and neck for extended periods and are often heat-treated during styling. They may expose consumers via inhalation, dermal contact, or ingestion of leached chemicals, particularly if chemicals transfer to the hands or mouth.

Considering these risks, the current paper sought to chemically profile 44 hair samples, including 43 commercial products and one pooled donated hair sample.

Advanced screening maps hidden chemical mixtures

The researchers used nontargeted analysis to identify as many chemicals as possible in the samples and applied suspect screening to match detected compounds against existing databases. Samples were analyzed using two-dimensional gas chromatography coupled with high-resolution mass spectrometry. The resulting mass spectra were compared to entries in the National Institute of Standards and Technology library and processed using the Highlight machine-learning platform.

Synthetic and natural fibers show chemical diversity

The 44 samples comprised 28 specified polymer products, including 16 Kanekalon, 3 Aquatex, 2 Spetra, and 7 Mastermix, as well as 8 unspecified synthetic fibers and 8 natural fibers. The natural group included four human hair products, two banana fiber products, one silk eyelash extension, and one pooled sample of donated human hair clippings. All Kanekalon samples were labeled flame-resistant, and additional unspecified synthetic products also claimed flame-retardant properties. In total, ten products carried heat-resistance claims.

Chemical categories

The analysis revealed 933 chemical signatures, meaning features detected by the analytical platform that do not necessarily represent fully identified chemicals. These signatures were detected 5,275 times across all samples. From these, 169 chemicals were putatively or definitively identified at confidence levels 1 or 2, meaning that the majority of detected signatures were not structurally confirmed.

Structural clues and public hazardous chemical lists were used to classify the identified chemicals into ten groups. These included distinct structural categories such as halogenated aromatics, halogenated non-aromatics, other aromatic heteroatom-containing compounds, other non-aromatic heteroatom-containing compounds, hydrocarbon groupings, and a category for unknowns. The study prioritized chemicals of concern, including organohalogen flame retardants, phthalates, and organotins, which are associated with endocrine disruption or carcinogenic potential.

Biobased fibers were generally more chemically complex than synthetic fibers, with raw human hair showing the greatest diversity of signatures, including both synthetic and naturally derived chemicals. Kanekalon samples had the fewest signatures. Unspecified synthetic fibers had the highest median number of total signatures and hazard-list chemicals. However, the “nontoxic” product had fewer than 50 signatures, compared with more than 200 for most other unspecified samples.

Halogenated aromatic signatures appeared across all synthetic fiber categories, particularly in unspecified fibers, though not in every individual sample. Overall, the greatest total numbers of chemicals and chemical signatures fell within categories not specifically defined as hazardous, including “other hydrocarbon” and “other non-aromatic heteroatom” groups.

Hazard-list chemicals

Of the 169 identified chemicals, 48 appeared on at least one public hazard list. Moreover, 91% of samples contained one or more chemicals listed under California’s Proposition 65. Only two samples, one unspecified synthetic fiber and one Spetra product, had no detected hazard-list chemicals.

Halogens

Chlorine levels were very high in Kanekalon and Aquatex samples, consistent with the chemical composition of their underlying polymers. Spetra samples had no detectable halogens, supporting their chloride-free labeling. Mastermix samples contained bromine in all cases, and some also showed low levels of fluorine, possibly related to color-stabilizing additives. Unspecified synthetic fibers varied widely in halogen content and often exhibited the highest overall halogen levels.

Fluorine and bromine were detected in select synthetic categories, with bromine consistently observed in Mastermix samples and fluorine detected in some Mastermix and Aquatex products. A targeted assay for 40 PFAS compounds did not detect those specific PFAS, although the authors note that many PFAS types, including certain neutral and ultrashort-chain compounds, were not covered by the assay.

Other chemicals

Phthalates were found in approximately half of the samples, with the greatest variety detected in biobased fibers. Banana fiber products labeled as “phthalate-free” nonetheless contained hazard-list chemicals, including bis(2-ethylhexyl) phthalate (DEHP). Four types of flame retardants were detected across the samples. Unknown chemicals classified at confidence level 4 were most commonly detected in unspecified and banana fiber samples.

Organotins

Organotins are commonly used as stabilizers in polyvinyl chloride (PVC) polymers and are classified as substances of very high concern in the European Union. Reported hazards include mutagenicity, reproductive and immune toxicity, and skin sensitization. No previous study has monitored organotin exposure related to hair extension use at the population level.

Organotin compounds were present in 10% of the samples and were detected exclusively in unspecified synthetic fibers. In some cases, tin concentrations exceeded 0.4% by weight. The European Union prohibits the use of certain dibutyltin compounds in general consumer items when tin concentrations exceed 0.1%. Tin was also measured in water and weak-acid leachates, suggesting the potential for leaching under use-relevant conditions and indicating that a mild acid prewash would not fully remove these compounds.

Strengths and limitations

This study applied nontargeted analysis in a novel way to profile the chemical composition of hair extensions, addressing an understudied potential source of consumer exposure. It examined both synthetic and natural fibers across a wide chemical space.

However, more than 80% of the detected chemical signatures could not be identified using existing library databases. The high-throughput nature of the data precluded manual characterization of each signal, and chemicals more amenable to liquid chromatography were not captured by the analytical approach. Further refinement of the findings will depend on the availability of additional mass spectra and analytical standards.

Transparency gaps highlight need for disclosure

The authors describe this work as the most comprehensive publicly available chemical analysis of hair extensions to date. However, the study does not establish exposure levels or quantify health risks associated with the detected chemicals.

Future research should focus on verifying the identities and sources of these compounds, quantifying their concentrations, and assessing real-world exposure pathways. Such work will be essential to inform consumer decision-making and guide policies that may require clearer ingredient disclosure from manufacturers.

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