For 15 years I managed my hormones with sleep, food, and training, and never once thought about my shorts. Then I read the research on endocrine disruptors, and the gear I wore two hours a day turned out to sit in the middle of it.
Endocrine disruptors are chemicals that interfere with the hormone system, and several common ones show up in synthetic activewear. That overlap is the reason Fight Form builds from natural fiber. Here's what the science actually says, and what it doesn't.
So what is an endocrine disruptor?
An endocrine disruptor is a chemical, or a mixture of chemicals, that interferes with any aspect of how your hormones work. That's the definition used in the Endocrine Society's 2015 scientific statement, the field's consensus document on the subject.1 The mechanism is more specific than "chemical bad." These molecules can mimic a natural hormone and trick a receptor into firing, or block a receptor so a real hormone can't bind.2
Your endocrine system runs on small signals. Hormones travel in tiny concentrations and tell tissues when to grow, when to burn fuel, when to make sperm, when to release testosterone. A molecule that resembles a hormone closely enough to bind the same receptor can scramble that signaling at the low amounts found in everyday products. That's the whole problem in one sentence.
What endocrine disruptors do to male hormones
In men, the concern centers on the hormones that govern testosterone and sperm production. The Endocrine Society statement gives male reproductive health its own section, covering semen quality and testicular endpoints alongside hormone signaling.1
Two chemicals do most of the work here, and both are common in synthetic gear. Phthalates, the plasticizers that keep plastic soft, have been associated with lower serum testosterone in men at ordinary exposure levels in large population data.3 Bisphenol A, or BPA, tracked with a reduced free androgen index and higher estradiol in adult men in a separate study.4 The links are associational, drawn from population data, and clothing is never isolated as the single source. Nobody has run the clean experiment of "wear synthetic shorts, measure your testosterone." But the pattern is hard to miss. The same families of chemicals keep landing on the wrong side of male hormone measures.
Why the low dose is the part people get wrong
Small doesn't mean safe here. The intuition that a tiny dose is automatically a harmless dose does not hold for endocrine disruptors. The Endocrine Society statement documents dose-responses that are non-monotonic, meaning a low dose can produce an effect that a higher dose does not, because hormone receptors evolved to respond to very small concentrations.1
Two things follow from that. A "trace amount" on a spec sheet is not automatically reassuring, because trace amounts are the range hormones already operate in. And exposure does not arrive one chemical at a time. The same statement defines a disruptor as a chemical or a mixture, because real life is a mixture: the waistband, the print, the gym dust, the food packaging, all at once.1 The honest way to read this is as a cumulative load. You lower it by removing the sources you actually control.
Where endocrine disruptors hide in men's activewear
In a typical pair of synthetic training shorts, the disruptors cluster in a few predictable places. Look at the printed graphics, the sublimated panels, and the rubberized grip on the waistband. All of it is made with plasticizers, the phthalate and BPA chemistry above. The fabric itself sheds microplastics. And water- and stain-repellent finishes can add PFAS, a separate class with its own hormonal and health record.
| Chemical | Where it shows up in activewear | What studies link it to in men |
|---|---|---|
| Phthalates | Plasticizers in prints, sublimated graphics, stretch waistbands | Lower serum testosterone (population data) |
| BPA | Plasticizers in coatings and rubberized panels | Lower free androgen index, higher estradiol |
| Microplastics | Shed by polyester and nylon fabric | Detected in human blood and testis tissue |
| PFAS | Water- and stain-repellent finishes | Endocrine, immune, and fertility effects |
I wrote the part-by-part breakdown of a fight short elsewhere, so I won't repeat it here. For the component view, are MMA shorts toxic? takes a short apart piece by piece, and PFAS in fight shorts covers the finishes and what has actually been tested.
First drop. 500 units. Late 2026.
Access before the public.
Why training gear raises the dose
Two pairs of shorts with the same chemistry aren't the same exposure. What moves a chemical out of fabric and into a body is heat, moisture, friction, and time in skin contact. Training maximizes all four at once.
A hard session runs hot and soaked for one to two hours, with the fabric pressed against you the entire time. Compression cuts and fitted liners increase the contact. And the part of male anatomy most relevant to the hormones above sits directly under the shorts, in the warmest, most enclosed spot on the body. What changes is the dose: how much of the chemistry moves into you, several times a week, for years. A combat athlete is closer to the worst case the exposure studies imagine than to the calm, dry wearer they usually model.
What the research finds in the body
The reason this moved from theory to something I act on is where the particles have turned up. Researchers have detected plastic particles in human blood,5 and a 2024 study found microplastics in 100 percent of the human testis samples it tested.6 The testis study could confirm only that the particles were present, not what they do there, so this is early science rather than a closed case. I take it seriously anyway.
I want to be careful with that, because the distance between "present in tissue" and "causes harm" is real and worth stating plainly. But set it next to the hormone associations and the direction is consistent: the same synthetic materials keep appearing where male reproductive health is measured. The precautionary call, lowering a source you can control, does not require waiting for the final study.
How to lower your exposure from gear
You can't control the food packaging or the gym dust. But the layer against your skin for hours a week is a variable you fully choose. Start there.
The reliable move is to remove the sources rather than chase a low number on a label. A natural fiber shell sheds no microplastics. A fluorine-free construction carries no PFAS finish. A clean, low-print build cuts the plasticizer load that rides in graphics and rubberized waistbands. A natural fiber liner keeps synthetic shedding off the skin in the spot that gets the most heat and contact.
That's the short Fight Form set out to build. The Fight Short and Training Short use an organic cotton and TENCEL lyocell shell, a merino wool brief liner, and a natural rubber waistband, with no polyester, spandex, or PFAS. The materials breakdown lists every fiber by name, and if you are deciding which cut to wear, the BJJ and MMA shorts buyer's guide sorts it by sport, inseam, and pockets.
The bottom line
Endocrine disruptors are chemicals that interfere with your hormones, and synthetic activewear is a small, avoidable source of several of them: phthalates and BPA in prints and waistbands, microplastics shed by the fabric, PFAS in finishes. In men, those chemistries track with lower testosterone, a lower free androgen index, and higher estradiol, and the particles now show up in human blood and testis tissue. None of it is acute poisoning, and none of it is fully settled. Both are true at once. Training gear is simply worn in the conditions that raise the dose, and the layer against your skin is the variable you control. That's why we build from natural fiber.