Are There Chemicals In Your Gym Clothes?
Yes. The question worth asking is which ones, how much, and whether any of it comes off onto you.
Here is what goes into synthetic activewear, in the order it gets added.
Antimony trioxide. The catalyst used to polymerise PET. It does not wash out because it is in the fibre, not on it. Present in 80 to 85% of all virgin polyester.
Disperse dyes. Polyester is chemically inert and will not hold colour without high heat, pressure and a stack of auxiliary chemicals. That is why synthetic kit comes in colours natural fibre cannot reach.
Anti-odour finishes. Added because the fibre smells. Usually silver or a quaternary ammonium compound. They wash out within a few cycles, which is why the smell comes back.
Softeners and coatings. Applied to make plastic feel less like plastic. Also where phthalates turn up, in plastisol prints and rubberised logos rather than the fibre itself.
The one that actually comes off.
Most of the above stays put. Antimony does not.
Testing published in Regulatory Toxicology and Pharmacology measured 125 to 470 micrograms per gram of antimony in finished polyester, and found a fraction of it migrating into artificial sweat under standard test conditions.
The first extraction released the most, which is why washing a new synthetic garment before wearing it is worth doing.
Antimony in finished polyester, micrograms per gram
Antimony is a polymerisation catalyst. It is only in polyester because polyester has to be made rather than grown. Source: Biver, Turner and Filella, 2021.
Natural fibre needs none of it. You cannot add a catalyst to something that grew.
The certifications that actually test for this.
OEKO-TEX Standard 100
Every component tested against a list of harmful substances. Extractable antimony is capped at 30 mg/kg. If a brand carries this, the testing has been done by a third party.
GOTS
For organic fibre. Requires at least 95% certified organic content for the organic label, bans chlorine bleach and toxic heavy metals, and restricts processing chemicals to an approved list. Audited annually across the whole supply chain.
Words that mean nothing
Natural. Clean. Non-toxic. Eco. None of these are defined, audited or enforceable. If a brand uses the adjective without naming the standard behind it, there is no standard behind it.
What we carry, and what we do not.
GOTS for the organic cotton. RWS for the merino. OEKO-TEX Made in Green for the finished garment, which requires the material testing plus manufacture in audited facilities. WRAP for the production sites.
No anti-odour finish, because merino does not need one. No softener, because the fibre is already fine enough. No disperse dye chemistry, because natural fibre takes colour without it.
Four certifications and a short ingredient list. That is the whole story.
Read the tag, not the campaign.
The composition label is the only part of a garment that cannot spin you. Turn it inside out and look. If it lists polyester, polyamide, nylon or elastane in any percentage, everything above applies to it.
No mystery blends. No proprietary technology.
The short version
Yes, there are chemicals in synthetic gym clothes. Antimony from manufacture, disperse dyes for colour, anti-odour finishes to mask a problem the fibre creates, and softeners to make plastic feel acceptable.
Natural fibre needs none of them, because it grew rather than being synthesised. Look for OEKO-TEX and GOTS on the label, and treat every unqualified adjective as decoration.
We cover what all this does to skin in is polyester bad for your skin, and the elastane question in alternatives to elastane and spandex.