The popular framing among wellness creators and eco-conscious consumers positions polyester as a single, monolithic problem. Plastic fiber. Microplastics. Full stop. The reality is more granular. One compound embedded in nearly all polyester textiles receives almost no attention in the consumer conversation: antimony trioxide, the catalyst used in the production of the majority of global PET.
What the popular framing says
Scroll through non-toxic activewear content on TikTok or Instagram and the narrative is consistent. Polyester is bad because it is plastic. Plastic sheds microfibers. Microfibers pollute oceans and possibly enter your body. The framing is not wrong, but it is incomplete.
The conversation rarely distinguishes between the polymer backbone itself (polyethylene terephthalate) and the residual chemicals left behind from manufacturing. Polyethylene terephthalate (PET) is the most common type of polyester used in textiles and antimony is present in 80-85% of all virgin PET because antimony compounds (mainly Sb2O3) are used as catalysts in its production. This is not a theoretical concern. It is a measurable, extractable residue present in the majority of polyester garments sold today.
When Mamavation tested 32 pairs of activewear for PFAS indicators, the investigation surfaced important data about forever chemicals. Yet antimony, which is present in virtually every polyester sample regardless of PFAS treatment, was not part of that testing scope. The compound sits in a regulatory blind spot: present in most polyester, subject to voluntary certification limits, but not restricted by any binding textile law in the United States or the European Union.
What the data actually says
The most rigorous study on antimony release from polyester textiles was published in Regulatory Toxicology and Pharmacology in 2021. Researchers at the University of Plymouth and University of Geneva determined the release of antimony (at total concentrations ranging from about 125 to 470 μg g⁻¹) from polyester textile samples designed to be in contact with human skin using standard artificial sweat solutions.
The key finding: between about 0.05 and 2% of total antimony (or 0.1-1 μg g⁻¹) was mobilized into artificial sweat. This is not a static number. Extraction rates changed with experimental conditions:
In other words, the conditions that define an intense workout (body temperature, acidic sweat, prolonged contact with compression garments) are precisely the conditions that maximize antimony mobilization from polyester fibers.
The regulatory context
There is no binding regulatory limit on antimony concentrations in polyester apparel in the United States or European Union. The EU Ecolabel sets a voluntary ceiling for total antimony in raw polyester fibers, but this threshold applies to fibers before wet processing, not finished garments.
The OEKO-TEX™ STANDARD 100 label requires that extractable antimony is less than 30 μg g⁻¹ for clothing textiles. This is a meaningful limit. It addresses extractable antimony rather than total content, which is the more relevant metric for skin exposure. However, OEKO-TEX certification is voluntary. The majority of activewear sold globally carries no antimony certification of any kind.
OEKO-TEX™ STANDARD 100 uses risk-based testing, with stricter limits for items worn close to the body like bras, underwear, and activewear. The more skin contact, heat, and sweat involved, the stricter testing thresholds.
The carcinogenicity question
In 1989, the International Agency for Research on Cancer (IARC) concluded that Diantimony Trioxide is possibly carcinogenic to humans (Group 2B). The US National Toxicology Program has subsequently strengthened this assessment.
The NTP concluded that antimony trioxide is reasonably anticipated to be a human carcinogen based on sufficient evidence of carcinogenicity from studies in experimental animals and supporting evidence from mechanistic studies. In experimental animals, inhalation exposure to antimony trioxide caused lung tumors in rats and mice of both sexes, adrenal gland tumors in female rats, skin tumors in male mice, and tumors of the lymphatic system in female mice.
It is important to note: these carcinogenicity findings are based on inhalation studies, not dermal exposure. The relevance to textile contact is indirect but not irrelevant.
Where the popular framing is right
The wellness community's instinct that polyester activewear carries chemical risks beyond microplastic shedding is correct. The mechanism is real: chemicals can migrate from textiles into sweat and subsequently be absorbed through skin.
A 2024 study from the University of Birmingham provided direct evidence for this pathway. The results showed that as much as 8% of the chemical exposed could be taken up by the skin, with more hydrated, or 'sweatier,' skin absorbing higher levels of chemical. This study examined brominated flame retardants in microplastics, not antimony specifically. But the mechanism, sweat-facilitated dermal absorption of polymer additives, applies broadly.
More sweaty skin resulted in higher bioavailability of PBDEs from dermal contact with MPs than dry skin. The principle is consistent: hydrated skin is more permeable than dry skin.
The concern is also directionally correct about activewear being a higher-risk category than casual clothing. Hair follicles and sweat and sebaceous gland density can influence dermal absorption. Different anatomical sites in humans display a hierarchy of absorption. The combination of compression, heat, sweat, and prolonged wear creates conditions that favor transdermal chemical transfer.
Where the popular framing is wrong, and the mechanism for why
The popular framing fails in two critical ways.
First, it conflates polyester-the-polymer with polyester-the-finished-garment. The PET polymer itself is chemically stable. The risk comes from residual manufacturing chemicals: antimony from catalysis, formaldehyde from wrinkle-resistant finishes, disperse dyes that can migrate under sweat conditions. When Ecocult had a garment tested that passed OEKO-TEX certification, the lab found "formaldehyde close to the limit, 9 ppm of antimony, .07 ppm of tetraethyltin, and .01 ppm of DMF." The garment technically passed. The consumer still experienced a reaction.
Second, the framing ignores the exposure pathway distinction. Dermal absorption of antimony from textile contact is not equivalent to inhalation exposure in occupational settings. The carcinogenicity data for antimony trioxide comes primarily from inhalation studies in industrial workers and laboratory animals. A consumer wearing polyester leggings is not experiencing occupational-level exposure via the same route.
However, this does not mean consumer exposure is negligible. Combining moisture, warm temperature, and increased blood flow to the skin contributed to an ideal environment for accelerating dermal absorption of several pesticides. The dermal pathway exists. What remains uncertain is the cumulative health significance of this specific exposure pathway over years of activewear use.
The relevant number is not how much antimony is in the polyester fiber. It is how much antimony is extracted under sweat conditions and subsequently absorbed through skin. The 2021 Plymouth study provides the first half of this equation. The dermal absorption coefficient for antimony under real-world activewear conditions remains incompletely characterized.
What this means for a product founder
If you are sourcing polyester for activewear, the antimony question is unavoidable. Here is what the data supports:
Require OEKO-TEX STANDARD 100 certification
The 30 μg g⁻¹ extractable antimony limit is the only standardized threshold that addresses the exposure-relevant metric. Total antimony content is less meaningful than extractable antimony. A fabric with 200 μg g⁻¹ total antimony but low extractability may pose less exposure risk than a fabric with 150 μg g⁻¹ total antimony and high extractability.
Ask about catalyst alternatives
Antimony trioxide is the dominant catalyst, but it is not the only one. Titanium-based and germanium-based catalysts exist. They are more expensive. Supply chains rarely default to them. But if antimony-free polyester matters to your brand positioning, these alternatives are technically available.
Consider the garment's use case
A polyester blouse worn over a cotton base layer in an air-conditioned office presents a different exposure profile than compression leggings worn during a 90-minute hot yoga session. Design choices (fiber selection, layering, intended use duration) affect total exposure.
Pre-wash instructions matter
The Plymouth study noted that since the first fraction of either extractions mobilized the greatest quantity of antimony, exposure can be minimized by washing articles before use. A pre-wear wash removes the most readily mobile residue. This is not a solution to the underlying chemistry, but it is a practical risk-reduction step.
For founders exploring the plastic-free activewear guide, antimony is one of several reasons to consider natural fiber alternatives. Merino wool, Tencel lyocell, and organic cotton are produced without antimony catalysis. They are not without their own manufacturing chemistry, but they sidestep this particular compound entirely.
OHZEHN-TEX™ requires full catalyst disclosure from polyester suppliers and defaults to OEKO-TEX STANDARD 100 compliance as a minimum threshold for any synthetic component.
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The peer-reviewed data is clear on the mechanism: antimony mobilizes from polyester into sweat, and sweat-moistened skin absorbs chemicals more readily than dry skin. What remains uncertain is the cumulative health significance of this exposure pathway over years of activewear use. The absence of regulatory limits does not mean the absence of risk. It means the risk has not yet been quantified to the satisfaction of regulators.
Sources
https://www.sciencedirect.com/science/article/pii/S0273230020302506 https://mamavation.com/product-investigations/non-toxic-activewear-guide-pfas-workout-leggings-yoga-pants.html https://vibrantbodycompany.com/blogs/education/oeko-tex-certified-meaning https://www.antimony.com/regulations-compliance/classification/ https://pmc.ncbi.nlm.nih.gov/articles/PMC8149478/ https://ntp.niehs.nih.gov/whatwestudy/assessments/cancer/completed/antimonyt https://www.birmingham.ac.uk/news/2024/toxic-chemicals-from-microplastics-can-be-absorbed-through-skin https://www.sciencedirect.com/science/article/pii/S0160412024002216 https://pmc.ncbi.nlm.nih.gov/articles/PMC7010093/ https://ecocult.com/does-oeko-tex-certification-mean-a-product-is-safe/ https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/skin-absorption https://wearbonta.com/blogs/news/oeko-tex-certified-vs-conventional-activewear-why-we-lead-in-non-toxic-performance https://ohzehn-tex.com/plastic-free-activewear/