1. The polyester fertility experiments
Last time I mentioned polyester and fertility, you lot went absolutely bananas. So I went back down the rabbit hole, and somehow it gets even stranger.
In one 1993 experiment, male dogs were made to wear underwear made from either polyester or cotton for two years. The polyester group developed lower sperm counts, poorer sperm movement and more abnormal sperm. After the polyester was removed, their sperm gradually recovered.
Then researchers did a similar experiment with35 female dogs wearing underwear made from polyester, polyester/cotton, cotton, wool, or no underwear for 12 months. Eight dogs wearing polyester-containing fabrics developed lower progesterone during oestrus and failed to conceive. After the underwear was removed, their progesterone returned to normal and they subsequently conceived. The researchers proposed that electrostatic fields generated by the fabric might have interfered with ovarian function.
And then there's the human study.
Fourteen fertile men wore a polyester sling around their balls, day and night, for a year. Every one of them eventually reached azoospermia — meaning no detectable sperm in their semen — after roughly five months. Once the polyester was removed, sperm production returned.
The theory put forward by the researcher was that electrostatic charges generated by polyester could interfere with reproductive function.
Now, an enormous caveat before anyone throws £600 worth of gym kit into a skip:these were tiny, unusual studies, largely conducted by the same researcher, and they haven't been convincingly replicated. They do not prove your polyester leggings are making you infertile.
But that's actually not the part I find most interesting. What interests me is how quickly reproductive hormones and fertility can apparently respond to our environment — and how little attention most of us pay to that until the day we decide we want a baby.
Maybe fertility deserves our attention long before then.
2. So what is poor fertility actually a symptom of?
Poor fertility isn't a diagnosis in itself. Sometimes it's a reproductive problem, but sometimes it's a clue that something bigger is going on.
Your body needs enough energy, good sleep, functioning thyroid and sex hormones, manageable stress and adequate nutrients to keep reproduction running properly. When those things start going wrong, reproductive function can be one of the systems that takes the hit.
In women that might show up as irregular or disappearing periods, inconsistent ovulation or changes in libido. In men it can look like lower testosterone, poorer sperm production, reduced libido or changes in sexual function.
And that's why this matters even if babies are nowhere near your plans.A body that's struggling to maintain normal reproductive function may also be struggling with energy availability, recovery, metabolic health, stress or hormonal signalling more broadly.
Think of fertility less as a pass/fail baby-making test and more as another vital sign worth paying attention to.
You don't wait until you want a child to start caring about your sleep, blood pressure or blood sugar.
Why should your reproductive health be any different?
3. What's hiding in plain sight?
This is where the polyester story becomes much bigger than polyester.
Synthetic clothing gets our attention because it's weird and tangible, but our reproductive systems are exposed to a constant combination of modern pressures: bad diet, chronic stress, poor sleep, shift work, excessive heat, environmental chemicals and simply not giving the body enough energy to recover properly.
Trying to eliminate every possible exposure would drive you mad, and the evidence behind each one varies massively. The goal isn't to become terrified of your leggings, your frying pan leaching chemicals and the BPA ridden receipt someone just handed you.
It's to recognise that hormones don't exist separately from your lifestyle.
If your menstrual cycle disappears, your libido suddenly falls off a cliff, erectile function changes or other aspects of reproductive function noticeably shift, don't dismiss it simply because you're not trying to have children.
Your fertility is not just your ability to make a baby. It's one piece of information about how your body is functioning right now.
HEALTH HACK
Get a blood work MOT.
I can’t recommend blood work enough if you want to know what’s actually going on under the hood. How you feel matters, but tangible numbers give you something concrete to work with rather than guessing.
It can highlight deficiencies, poor recovery or areas that need more attention. Think of it as a baseline for your health, not something you only investigate when something goes wrong.
Contact your GP, or for a quicker and often more comprehensive service, tryMedichecks, Thriva or Randox Health.
