A study once found that polyester could temporarily bring men's sperm counts to zero.
But before you throw out your entire underwear drawer, there's more to the story.
Let's talk about what's happening in your pants.
Polyester is everywhere. It's in your gym shorts, your shirts, your socks, even in your kid's toys.
It's cheap, durable, stretchy and relatively easy to care for. There's a reason clothing manufacturers love it.
But lately the internet has been doing its thing, and waging guerilla warfare against the reputation of plastic garments.
Is polyester underwear actually bad for men?
Depending on who you ask, polyester is either an ordinary fabric or a testosterone frying, fertility crushing menace to your manhood.
The truth is more nuanced.
Because researchers really did conduct experiments involving polyester underwear and fertility. And one of those experiments produced a result that's eyebrow raising at worst.
Let's get into it.
The Polyester Experiment That Made Men's Sperm Counts Drop to Zero
In 1992, researcher Ahmed Shafik published a study titled Contraceptive Efficacy of Polyester-Induced Azoospermia in Normal Men.
The experiment involved 14 healthy men who wore specially designed polyester slings around their scrotums continuously for 12 months.
'Ouch' you think. Rightfully so.
These weren't ordinary boxer briefs. They were polyester supports designed to remain in close contact with the scrotum, day and night. The sartorial equivalent of a drag queen tucking for almost A YEAR STRAIGHT.
The researchers monitored semen samples, testicular volume, temperature differences, and reproductive hormone levels throughout the experiment.
The results were straightforward, but in 2026 are misrepresented for special interests on a regular basis.
CONCLUSION: All 14 participants developed azoospermia
Azoospermia is the medical term for having no sperm detectable in the semen.
On average, participants reached that point after approximately 140 days of wearing the polyester slings.
That's a remarkable finding, particularly considering that the participants had normal fertility at the beginning of the study.
But........
Did Polyester Lower Their Testosterone?
No significant decrease in reproductive hormone levels was detected
Despite the participants experiencing dramatic changes in sperm production, the researchers did not find statistically significant changes in their reproductive hormones.
Testosterone production and sperm production are related, but they're not the same biological process.
A man can have normal testosterone levels and still experience severely impaired sperm production.
And that's precisely why claiming that this experiment proves polyester underwear destroys testosterone is misleading.
The study found an association between continuous polyester sling use and suppressed sperm production under its experimental conditions.
It did not demonstrate that polyester causes testosterone depletion.
Regardless of what kind of underwear you sell, it's important to truthfully reporesent what the scientific method has uncovered.
What Happened When the Men Stopped Wearing Polyester?
Here's another detail that frequently gets left out of doomer social media bait.
Their sperm production rapidly recovered.
After the 12-month experiment ended, the participants stopped wearing the polyester ball crushers.
Their sperm concentrations returned to baseline levels after an average of approximately 157 days.
Testicular volume and temperature differences also returned toward their original measurements.
And among the five couples who planned to conceive afterward, all five achieved pregnancies.
That doesn't make the original findings not noteworthy.
But it does mean the study observed a reversible effect under its specific conditions. It's not proof of permanent infertility caused by everyday polyester clothing.
Why Did the Researchers Think Polyester Affected Sperm Production?
The researchers proposed two possible explanations.
1. Electrostatic charges
Polyester can accumulate static electricity through friction.
If you've ever pulled a polyester shirt out of the dryer and heard it crackle, you've experienced this phenomenon firsthand.
The researchers measured electrostatic potentials associated with the polyester slings and proposed that the resulting electrical field might interfere with sperm production.
Another experiment involving 21 volunteers found higher electrostatic measurements with polyester underwear than with cotton underwear.
Interesting? Absolutely.
Definitive proof of a fertility-damaging mechanism? Not remotely.
The idea that fabric-generated electrostatic fields can meaningfully disrupt sperm production inside the human body remains a hypothesis that hasn't been convincingly established through independent research.
2. Changes in testicular temperature regulation
There's a reason your testicles live outside your body.
Normal sperm production depends partly on maintaining a temperature below core body temperature.
The 1992 researchers observed changes in the temperature difference between the rectum and testes during sling use.
They suggested that disrupted temperature regulation might help explain the findings.
Unlike the proposed electrostatic mechanism, the relationship between testicular heat exposure and sperm production has a substantial physiological basis.
However, that doesn't mean every polyester garment causes meaningful overheating, or that every increase in scrotal temperature leads to infertility.
Fabric construction, garment fit, airflow, and environmental conditions all matter.
So Does Normal Polyester Underwear Make Men Infertile?
Here's where we need to separate a fascinating experiment from an established medical conclusion.
We do not have convincing evidence that wearing ordinary polyester boxer briefs causes infertility in men.
The original sling experiment involved only 14 participants, lacked a comparable randomized control group, and used an unusual garment worn continuously for an entire year.
That's a very different situation from putting on clean boxer briefs in the morning and changing them the next day.
And other research hasn't consistently reproduced the dramatic results.
In a separate study involving 21 healthy men, researchers examined polyester-lined athletic supports worn during the day for 52 weeks.
The supports increased scrotal temperature by approximately 0.8–1.0°C.
Yet the researchers did not observe significant deterioration in sperm concentration, motility, morphology, or several other measures of sperm function.
In other words, not every experiment involving polyester supports has produced the same fertility effects.
That matters.
Science isn't about finding one alarming study and declaring the case closed. It's about looking at the full body of evidence, including findings that complicate the original theory.
What About Tight Underwear and Sperm Count?
There is some evidence suggesting that underwear style and fit may be associated with differences in sperm production.
A 2018 study of 656 men attending a fertility center found that men who primarily wore boxer shorts had approximately 25% higher sperm concentrations and 17% higher total sperm counts than men who typically wore other underwear styles.
The boxer-wearing group also had lower levels of follicle-stimulating hormone, or FSH, a hormone involved in regulating sperm production.
Buuuuuut this was an observational study.
It couldn't establish that the underwear itself caused those differences.
And it wasn't designed to determine whether polyester, cotton, or another particular fabric was responsible.
Other research examining couples trying to conceive has found no significant association between underwear choice and how long it took them to achieve pregnancy.
So while avoiding excessive heat and choosing comfortable, appropriately fitting underwear may be reasonable, the evidence doesn't justify treating a particular underwear style as a guaranteed fertility intervention.
Is Polyester Underwear Bad for Testosterone?
Let's stick to Einstein's method.
There is currently no convincing human evidence that ordinary polyester underwear lowers testosterone levels.
The famously referenced polyester sling experiment did not detect significant changes in hormone levels.
The animal studies sometimes cited in discussions of polyester and fertility have also reported sperm-production changes without statistically significant hormonal changes.
That doesn't establish that polyester is completely harmless under every imaginable circumstance.
It means the specific claim that wearing polyester underwear tanks your testosterone isn't supported by the available evidence.
There's a difference.
If a brand tells you its underwear will increase your testosterone simply because it doesn't contain polyester, you should consider if you want to patronize someone who hard sells you with stretched truth.
Your hormones are at the mercy of your diet, lifestyle, and the guidance of a certified endocrinologist.
So Why Would Anyone Avoid Polyester Underwear?
Even without dramatic claims about testosterone there are perfectly reasonable reasons to prefer other fabrics.
Polyester is synthetic, and the way a polyester garment feels depends heavily on its construction.
Quality polyester (yes there are different grades) is lightweight and effective at moving moisture away from the skin.
Other polyester garments can feel less comfortable, retain odors, or create an unpleasant experience during long, sweaty days.
Meanwhile, fabrics like cotton, modal, and bamboo-derived viscose offer different combinations of softness, absorbency, drape, and moisture management.
No single fiber automatically wins every category. It's a preferential game of whack-a-mole.
And contrary to what some marketing might suggest, bamboo viscose isn't a magical health fabric either. It's a manufactured cellulosic fiber produced through chemical processing.
The sensible approach is to choose underwear based on its actual performance: comfort, fit, breathability, support, durability, and how it feels against your skin.
Not on unsupported promises about transforming your hormone levels.
Our Take at Maison Gallus
We think men's underwear should do everything well.
It should feel good against your skin.
It should provide support.
It should be comfortable, yet flattering.
And it definitely shouldn't require a scientific conspiracy theory to convince you to buy it.
At MG we use bamboo-derived viscose in our flagship Dawnbreakers boxer briefs because we like its softness, feel, and comfort characteristics.
We're not going to promise that switching underwear will double your testosterone.
We're not going to tell you polyester is secretly a form of birth control (because otherwise it would already be a billion dollar product).
And yeah we're absolutely not going to pretend a 14-person experiment from the early 1990s settles the claim that "polyester gives you female levels of T".
Your underwear is one of the few things you wear against your most sensitive anatomy every single day. You might as well choose something that feels great.
Your package deserves some consideration.
Frequently Asked Questions
Does polyester underwear lower sperm count?
Some small experimental studies have reported reduced sperm production associated with prolonged polyester garment use, including a 1992 study in which 14 men developed reversible azoospermia while wearing specialized polyester scrotal slings. However, these findings have not established that ordinary polyester underwear reduces sperm counts during typical daily use.
Does polyester underwear lower testosterone?
There is no convincing evidence that normal polyester underwear lowers testosterone. The well-known polyester sling study reported no statistically significant changes in measured reproductive hormone levels.
Can polyester underwear cause infertility?
There is insufficient evidence to conclude that ordinary polyester underwear causes infertility. The most dramatic experimental findings involved unusual, continuous-use garments and small sample sizes.
Is cotton or bamboo underwear healthier than polyester?
Neither cotton nor bamboo-derived viscose has been conclusively demonstrated to improve testosterone or fertility compared with polyester. The best choice depends on comfort, fit, fabric construction, and personal preferences.
Is polyester underwear safe to wear every day?
For most men, ordinary polyester underwear is not known to cause infertility or testosterone suppression. People who experience irritation, discomfort, or excessive heat may prefer different materials or garment designs.
Scientific References
-
Shafik A. (1992). Contraceptive efficacy of polyester-induced azoospermia in normal men. Contraception. https://pubmed.ncbi.nlm.nih.gov/1623716/
-
Shafik A. (1992). Effect of different types of textile fabric on spermatogenesis. I. Electrostatic potentials generated on surface of human scrotum by wearing different types of fabric. https://pubmed.ncbi.nlm.nih.gov/1503251/
-
Shafik A. (1993). Effect of different types of textile fabric on spermatogenesis: an experimental study. https://pubmed.ncbi.nlm.nih.gov/8279095/
-
Effect of increased scrotal temperature on sperm production in normal men. (1997). https://pubmed.ncbi.nlm.nih.gov/9240266/
-
Type of underwear worn and markers of testicular function among men attending a fertility center. (2018). https://pmc.ncbi.nlm.nih.gov/articles/PMC6530653/
-
Choice of underwear and male fecundity in a preconception cohort of couples. https://pmc.ncbi.nlm.nih.gov/articles/PMC6214186/
This article is for general educational purposes and is not a substitute for medical advice. Anyone concerned about fertility or hormone levels should consult a qualified healthcare professional.