Scientists find 169 chemicals (and 48 of them are harmful) in hair extensions

©Lindsay Cash via Unsplash

The global market for hair extensions is worth billions of dollars and is expected to exceed 14 billion by 2028. Yet despite their widespread use, these products are still among the least regulated and least studied cosmetics in the market.

A group of researchers from the Silent Spring Institute looked into that gap. In the journal Environment & Health, the researchers published what they themselves describe as "the most complete public analysis ever conducted on hair extensions".

What's hidden in hair extensions?

To find out what's really in hair extensions, the researchers sourced 43 of the top-selling products on the U.S. market, selected based on their popularity on social media, label claims and variety of materials: from synthetic Kanekalon fibers to raw, human hair, as well as banana fiber, silk and hybrid blends.

Each sample was analyzed with two-dimensional gas chromatography coupled with high-resolution time-of-flight mass spectrometry (GCxGC-TOF-MS), an advanced technique that can detect volatile and semi-volatile compounds even in very small traces. Data processing was entrusted to Highlight, an AI platform developed specifically for large-scale, non-targeted chemical analyses.

The result? As many as 933 different chemical signatures, accounting for a total of more than 5,200 detections across all samples combined. Of these, the researchers were able to confidently identify 169 chemicals, then estimated their potential risk.

The substances of greatest concern

Among the compounds identified, 48 are listed on at least one of the official hazardous substance lists, including California's well-known Proposition 65, which mandates warning labels for products containing carcinogens or reproductive toxins. 91% of the samples analyzed contained at least one substance from this list.

These are the categories that rang the most alarm bells:

Organotin compounds

Nearly 10% of the samples analyzed contained organotin compounds, a chemical class normally associated with PVC stabilizers and antifouling marine paints. Four samples of synthetic fibers of unspecified type showed tin concentrations above 0.4% by weight, a value exceeding the limit set by the European Union (0.1%).

Among the compounds identified are mainly dibutyldichloroethin, classified in the EU as a substance of particular concern and banned in consumer products above certain levels, and tributyltin chloride, a known endocrine disruptor that causes metabolic changes in laboratory animals similar to metabolic syndrome, in addition to insulin resistance and lipid disorders. This substance was historically widely used in marine paints, but has since been banned due to its pronounced aquatic toxicity.

Of particular concern, leaching analyses showed that these compounds can partially migrate in water under conditions that mimic a normal shower, with even stronger leaching in an acidic environment - such as that created with apple cider vinegar, a home remedy often recommended as a pre-wash treatment for synthetic extensions before use.

Flame retardants and halogenated compounds

Most synthetic extensions analyzed are marketed as flame retardant or heat resistant, properties achieved by incorporating halogenated compounds into the polymer. All Kanekalon fibers showed very high concentrations of chlorine - up to 277,000 micrograms per gram - in line with the presence of a vinyl chloride polymer and chlorinated flame retardants.

In contrast, high levels of bromine were found in Mastermix fibers, between 25,000 and 44,400 micrograms per gram, indicating brominated polymers or brominated flame retardants. Aquatex fibers, sold as water-repellent, contained significant concentrations of fluorine: a possible signal for the presence of PFAS substances, the infamous 'forever chemicals'. even though available targeted analyses did not allow confirmation of specific PFAS.

Phthalates, nitroaromatics and known carcinogens

Among the other confirmed or provisionally identified substances on hazard lists are bis(2-ethylhexyl) phthalate (DEHP), a plasticizer with effects on the reproductive system, dibutyl phthalate, styrene (probably carcinogenic), tetrachloroethane (highly toxic to liver and kidneys) and benzophenone, found in numerous samples of varying types, including Kanekalon, Mastermix and even some extensions of human hair. The insecticide permethrin was also found in a sample of raw human hair, presumably as a residue of insect treatment during processing.

Who is most at risk?

For many consumers, hair extensions are not a product you use once in a while: they are worn for days to weeks, in direct contact with the scalp, neck and skin. They are wet in the shower, heated with straighteners and blow dryers, and sometimes worn by children. Hairdressers deal with them daily.

The researchers point out an important issue of health justice: in the United States, more than 70% of black women use hair extensions at least once a year, while among white women the proportion remains below 10%. This is a market that particularly weighs on a community that is already disproportionately exposed to environmental pollution and which, due to lack of product transparency and limited regulatory oversight, must (out of necessity) make its choices virtually 'blind'.

'Green' claims not always reliable

For extensions sold as ecological or nontoxic, the results are striking. Spetra fibers, labeled 'toxin-free' and 'phthalate-free', were found to be among the cleanest of all the products studied, in line with claims. But the banana fibers - sold as biodegradable, PVC-free and phthalate-free - did contain bis (2-ethylhexyl) phthalate in both samples analyzed.

Only two products from the full panel contained no chemicals on any hazard list. That result shows that compliance with certain standards is possible, but by no means the rule.

What the researchers call for

The study's authors call for more transparency about fiber composition, stricter regulations - especially for organotin compounds, which are already banned in the EU but not in the US - and more attention from health authorities.

Practically, they recommend further investigation of exposure routes (inhalation, skin contact, ingestion), especially among the most vulnerable groups, and the development of more accurate quantification methods for the compounds identified. They further encourage manufacturers to reformulate their products and eliminate hazardous substances, pointing out that safer alternatives are already on the market.

How we can protect ourselves

Although the study covers products sold in the United States - where cosmetic legislation is less stringent than in the European Union - the problem is no stranger to the European market, where some products are imported through online channels or through barbershop wholesalers of dubious provenance.

Some practical tips to reduce exposure:

- Preferably choose extensions made from untreated human hair, which usually contain fewer synthetic chemicals than synthetic fibers.

- Check whether the products purchased bear a CE mark, as a minimum guarantee that they meet European standards.

- Avoid heating synthetic fibers unnecessarily, as heat accelerates the release of volatile compounds.

- Ventilate the room during and after inserting the extensions.

- Ask manufacturers for maximum transparency about the composition.

(©Environment & Health via GreenMe 2026/Managing Editor: Julie Morgan - The Press Junction/Picture: ©picture alliance/dpa/dpa-POOL | Peter Kneffel)