Four Fabrics. Fifty Men. Twelve Months. Only Two Groups Had A Problem — And Both Of Them Were Wearing Polyester.

Fifty Potent, Sexually Active Men. Five Groups. One Variable: The Fabric.

Dr. Ahmed Shafik ran the kind of experiment nobody runs anymore. He recruited fifty men — all potent, all sexually active at baseline — and split them into five equal groups. Four groups were given underpants made from a single textile each. The fifth was the control. Then everyone went about their lives for a year.

Sexual behaviour was assessed at baseline, at 6 months, at 12 months, and again 6 months after the underwear was removed. The measure was the ratio of potent intromissions to mounts — the I/M ratio — with a response counted as potent only if the man achieved erection, intromission and ejaculation. Alongside that, Shafik measured the electrostatic potentials generated on the penis and scrotum using an electrostatic kilovoltmeter.

Both Polyester Groups Dropped Significantly. Both Natural-Fibre Groups Didn't Move.

At both the 6-month and 12-month checks, the I/M ratio in the polyester and poly-cotton groups was significantly reduced compared with their own pre-test baseline and with the controls, at p < .001. Two patterns fell out of the data, and both of them point the same direction: the more polyester, the worse the result — and the longer it was worn, the worse the result.

That dose-response relationship is the part worth sitting with. If the effect were noise, you wouldn't expect more polyester and more time to both make it worse in the same consistent direction. The cotton and wool groups, meanwhile, showed insignificant changes for the entire study period — they were simply unaffected.

The Polyester Pants Generated An Electrostatic Field. The Cotton And Wool Generated None.

This is where the study gets interesting. Shafik didn't just record the outcome — he measured a physical difference between the fabrics. The polyester-containing pants generated electrostatic potentials on the penis and scrotum. The cotton and wool textiles generated none at all. Not less. None.

His proposed explanation was that those potentials could induce electrostatic fields in the intrapenile structures, and that this could account for the diminished sexual activity. In his companion work he measured roughly 338.9 V/cm² across the scrotal area on 100% polyester, against a zero reading on 100% cotton.

Be clear about what that is: a plausible mechanism the author proposed to explain his own findings, not a proven causal pathway. Shafik measured the field and observed the decline; he did not demonstrate that one produced the other. We'd rather tell you that than oversell it.

Six Months After They Took The Polyester Off, Everything Went Back To Baseline.

This is the single most useful sentence in the whole paper, and it's the reason we built a company instead of just writing a scary blog post. Six months after removal of the underpants, the I/M ratio had returned to pre-test levels in both of the groups that had worn polyester-containing pants.

Whatever the polyester was doing, it wasn't permanent. The variable was the fabric, and the fabric is the one thing in this entire conversation you can change this week without a prescription, a supplement, or a single lifestyle sacrifice.

What This Study Doesn't Prove. We'd Rather You Hear It From Us.

Fifty men across five groups means ten men per arm. That is a small study. It comes from a single research group — Shafik published a related body of work on textiles and reproductive function through the 1990s — and it has not been widely replicated since. The I/M ratio is an unusual outcome measure for human research, and any self-reported sexual-behaviour data carries the obvious risks.

So no, one 1996 paper with ten men per group does not settle the question of what polyester does to the human body. Nobody should tell you it does, and we won't. What it does do is put a specific, measurable, peer-reviewed finding on the table that the underwear industry has had thirty years to respond to and hasn't.

Here's the asymmetry that actually matters. If the research is wrong, you wore really comfortable certified organic cotton for no reason. If it's right, you avoided the whole thing for the price of switching what's in your drawer. You don't need certainty to make that trade — you just need to stop wearing the plastic.