The fiber is not the whole story.
Polyester or nylon gets most of the attention when people discuss toxic chemicals in workout clothes. Those concerns are legitimate. But the base fiber is just the starting point. For women building a clean activewear wardrobe, understanding what happens after the fiber is produced is where the picture gets more complicated.
PFAS: The Finish That Stays
Per- and polyfluoroalkyl substances (PFAS) are a class of synthetic chemicals used in durable water repellent coatings, stain resistance treatments, and some odor-control finishes applied to activewear. They are sometimes called forever chemicals because they do not meaningfully break down in the environment or in the human body. For a comprehensive reference on PFAS in activewear, including how they enter garments, what the health research shows, and how to avoid them, the dedicated guide to PFAS in activewear covers it in full.
The EPA has linked PFAS exposure to thyroid disruption, immune system suppression, increased cholesterol levels, and elevated risk of certain cancers. PFAS compounds have been detected in the blood of virtually all Americans, according to CDC biomonitoring data, accumulating through food, water, air, and contact with treated surfaces, including clothing.
The issue moved into mainstream consumer awareness in April 2026 when the Texas Attorney General issued a Civil Investigative Demand to Lululemon, investigating whether the company misled consumers about the potential presence of PFAS in activewear marketed specifically to health-conscious buyers. The investigation examined Lululemon's restricted substances list, testing protocols, and supply chain practices. Lululemon stated it had phased out PFAS from its products in early 2024, acknowledging the chemicals had previously been used in its durable water repellent products. A separate class action lawsuit had already been filed in California, alleging Lululemon misled consumers through its sustainability advertising campaign while its clothing contained PFAS.
The Lululemon case illustrates a broader problem. A brand can add a chemical to its restricted substances list and still have products in circulation that predate that policy. A brand can market itself as wellness-focused while using finishing chemicals that contradict that positioning. And the consumer, reading a label that lists only fiber content, has no way to know any of this without independent verification.
Many activewear brands have made PFAS commitments. Whether those commitments are reflected in finished garments, verified by third parties, and applied to the full product range rather than a subset are separate questions. The label PFAS-free on a finished garment is not always independently tested.
Phthalates: The Plasticizers in Synthetic Fabric
Phthalates are a class of chemical plasticizers used in the manufacture of synthetic polymers, including polyester and PVC-based materials. They are also used in some printing inks applied to garments, including sublimation dyes common in patterned activewear.
Phthalates are endocrine disruptors. The National Toxicology Program has concluded that several phthalates are reproductive and developmental toxicants in animal studies. Human epidemiological research has associated phthalate metabolite levels with disruptions to thyroid hormone and testosterone levels. A review published in the International Journal of Hygiene and Environmental Health (Heudorf, U., et al., 2007) summarized phthalate exposure pathways and endocrine-disrupting mechanisms based on available human and animal data.
Phthalates are not bonded permanently into finished fabrics. They migrate out of the material over time, particularly under heat and friction, both of which are defining conditions of exercise. Wearing synthetic activewear during a workout creates conditions that favor phthalate migration toward the skin.
Formaldehyde: The Wrinkle-Free Finish
Formaldehyde-based resins are used as anti-wrinkle, shape retention, and shrink resistance treatments in textile finishing. Formaldehyde is classified as a human carcinogen by the International Agency for Research on Cancer (IARC). It is also a respiratory irritant and skin sensitizer at lower concentrations.
Textile formaldehyde levels in some garments, particularly those manufactured without strict chemical limits, can exceed the thresholds that the OEKO-TEX Standard 100 certification restricts. Garments with this certification have been tested for formaldehyde content and must meet limits that vary by garment category and intended wearer.
Research has shown that formaldehyde release from textiles increases under humid conditions. During exercise, when sweat creates a humid microclimate between the garment and the skin, release rates from treated fabrics can be higher than under dry conditions, adding to the case for certified garments in high-sweat activity contexts.
Heavy Metal Dyes
Textile dyes, particularly azo dyes and some reactive dyes used to achieve intense, stable colors in synthetic fabrics, can contain or release heavy metals including chromium, cobalt, cadmium, and lead as part of the dye chemistry or as contaminants in lower-quality dye formulations.
Heavy metals accumulate in the body over time. Chromium VI is classified as a human carcinogen by IARC. Cadmium and lead are established developmental toxicants. The primary concern with dye-related heavy metals in clothing is dermal absorption, particularly under the conditions of exercise: elevated skin temperature, open pores, and extended skin contact. The European REACH regulation restricts many harmful dye components in products sold in the EU. OEKO-TEX Standard 100 testing covers heavy metal content in the finished garment.
What Certification Actually Covers
OEKO-TEX Standard 100 is the most widely recognized independent certification for harmful substance testing in finished textiles. It tests for over 100 substances including PFAS (specific compounds), phthalates, formaldehyde, heavy metals, pesticide residues, and pH. Garments must be retested every year and meet tiered standards based on intended use and contact with skin. For a full explanation of what OEKO-TEX covers, what it does not, and how fiber-level certification differs from finished-product certification, the dedicated page on OEKO-TEX and activewear explains it directly.
The EU Ecolabel covers both environmental production criteria and some chemical substance restrictions. It is a production standard as much as a product standard.
Neither certification eliminates all risk or covers every possible chemical. But they provide an independently verified baseline that self-reported brand claims do not. The Lululemon investigation is a direct example of why this distinction matters: wellness positioning and a restricted substances list are not the same thing as independent, ongoing verification of what is actually in a finished garment.
TENCEL Lyocell as a Starting Point
The chemical finishing concerns described above apply to any fabric that receives synthetic chemical treatments after fiber production. Choosing a better base fiber is the first step, not the complete answer.
TENCEL Lyocell, the primary fiber in Bellissima's Sempre line, starts from a lower-risk position than polyester or nylon: no plastic polymer chemistry, no petroleum-derived manufacturing inputs, and a base fiber that carries OEKO-TEX Standard 100 and EU Ecolabel certification at the fiber level. Kaplan et al. (2014), in Fibers and Polymers, documented TENCEL's structural moisture management advantages, which reduce the bacterial growth conditions that make some chemical odor-control treatments seem necessary in the first place.
The finishing question still matters. A TENCEL garment treated with a PFAS-based performance coating would carry a different chemical profile than an untreated one. What TENCEL does is start the garment at a better baseline and reduce the need for some of the chemical interventions that create problems downstream.
Bellissima's Sempre Leggings use 92% TENCEL Lyocell and 8% spandex. No PFAS treatments, antimicrobial chemical finishes, or formaldehyde-based treatments are applied to the fabric.
Reading a Label With More Information
The ingredients list for a garment is the fiber content. Everything else that was done to the fabric before you received it is mostly invisible on the label.
What visible signals exist: fiber certification, brand transparency about chemical finishing practices, third-party certifications, and the reputation of the manufacturing country for chemical regulation. These are imperfect signals. They are also the ones available.
Understanding the categories of chemical finishing that commonly occur in activewear manufacturing is not about alarm. It is about having the context to evaluate the signals correctly. For a full reference on which fabrics carry the highest risk profiles, toxic fabrics to avoid covers each one. For how to assess your current wardrobe, how to tell if your activewear is toxic works through the process. And for the full non-toxic evaluation framework, the non-toxic activewear buying guide covers what to look for and what to avoid at every step.
Sources
Texas Attorney General. (2026, April 13). Attorney General Ken Paxton Launches Investigation into Lululemon Over Potential Presence of Toxic Forever Chemicals in Activewear. texasattorneygeneral.gov.
U.S. Environmental Protection Agency. (2024). Our Current Understanding of the Human Health and Environmental Risks of PFAS. EPA.gov.
National Toxicology Program. (2012). NTP Monograph: Phthalates. US Department of Health and Human Services.
Heudorf, U., et al. (2007). Phthalates: Toxicology and exposure. International Journal of Hygiene and Environmental Health, 210(5).
International Agency for Research on Cancer. (2012). Formaldehyde. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol. 100F.
Kaplan, S., et al. (2014). Thermal comfort of lyocell and other fibers in active wear. Fibers and Polymers, 15(6).
OEKO-TEX Association. (2024). OEKO-TEX Standard 100 Testing Criteria. oeko-tex.com.
