Here’s something nobody warned you about: the underwear you grabbed off the shelf at Target last week might be doing more harm than a pair of jeans two sizes too small. And no, this isn’t about style or comfort — it’s about what the fabric is actually doing to your body while you go about your day.
The fabric in question? Polyester. That smooth, stretchy, affordable material that makes up more than 60% of the world’s clothing production — and almost certainly lines your underwear drawer right now.
You’re Basically Wrapping Yourself in Plastic
I don’t mean that metaphorically. Polyester is derived from petroleum — the same stuff we pump out of the ground to make gasoline. To create the fabric, small pellets of plastic are melted down and pushed through an extruder to form fiber strands. Those strands become the boxer briefs or bikini-cut underwear sitting in your dresser. When doctors say polyester underwear is like wrapping your private parts in plastic, they’re being literal.
Dr. Scott D. Miller, medical director at Wellstar Urology in Atlanta, has been blunt about this. He’s called pure polyester “probably the worst fabric for underwear,” explaining that while it’s lightweight, it’s neither absorbent nor breathable. Think about that for a second. The area of your body that sweats the most, stays the warmest, and has the most sensitive skin — and we’re covering it in something that traps every bit of heat and moisture against it.
What Happens When Things Can’t Breathe Down There
Your body naturally produces sweat in the genital area throughout the day. In breathable fabric, that moisture evaporates. Problem solved. But polyester and other synthetic materials hold that sweat against your skin like a wet blanket you can’t take off.
This creates a warm, damp environment — which is exactly what bacteria and yeast need to throw a party. Dr. Andrea Braden, a board-certified OB-GYN in Atlanta, puts it simply: air circulates better with cotton underwear versus polyester, and that circulation matters for vulvar health.
Women who regularly wear non-breathable underwear report more frequent yeast infections and bacterial vaginosis. For men, the consequences include jock itch, fungal infections, and — here’s where it gets really alarming — potential fertility problems. But we’ll get to that in a minute.
The Study That Made Every Man in the Room Uncomfortable
In the early 1990s, an Egyptian surgeon and researcher named Dr. Ahmed Shafik ran a series of experiments that should have made international headlines. In a 1992 study, 14 healthy men wore a polyester scrotal sling. Within an average of 140 days, every single participant became azoospermic. That means their sperm count dropped to zero.
Zero. Every single one of them.
In a parallel 24-month study from 1993, dogs wearing polyester showed dramatic drops in sperm count and motility, while dogs wearing cotton showed no changes at all. When the polyester was removed, most of the dogs recovered. A third human study that same year found that polyester had an “injurious effect” on male sexual function.
Dr. Shafik’s explanation? Polyester generates electrostatic fields that can disrupt testicular function and hormone signaling — an effect that cotton doesn’t produce. Now, these studies involved small sample sizes and a specialized device rather than ordinary boxers, but the results were dramatic and reversible. More recently, a 2018 Harvard study evaluating semen parameters from almost 700 men found that men who primarily wore boxers had a 25% higher sperm concentration than those who didn’t.
The temperature issue matters here too. For sperm production to work properly, testicles need to stay slightly cooler than core body temperature. Polyester traps heat against the body, potentially raising scrotal temperatures enough to impair both sperm production and quality.
The Chemicals You Never Knew Were in Your Underwear
Let’s say the moisture thing doesn’t bother you. Let’s say you’re not trying to have kids. There’s still the chemical problem — and this one is genuinely unsettling.
Recent studies have found that one in three underwear products contain bisphenols like BPA, BPS, and BPF. These are endocrine-disrupting chemicals that mess with your hormone system. They don’t just sit there inert in the fabric — they can be absorbed through your skin, especially in the warm, moist conditions that synthetic underwear creates.
Then there are PFAS, sometimes called “forever chemicals” because they don’t break down in the environment or in your body. These are used to make fabrics water-resistant and stain-proof. Dr. Marta Venier, an assistant professor at the University of Indiana in Bloomington, has pointed out that these products come into contact with extremely sensitive body parts where dermal absorption is higher than on regular skin.
PFAS exposure has been linked to liver and kidney damage, thyroid disease, behavioral disorders, and cancer. Studies have detected PFAS in 65% of children’s synthetic clothing. Even those trendy period panties? They’ve been found to contain dangerous levels of PFAS too.
An NBC investigation found fast-fashion retailers selling clothing coated with formaldehyde, phthalates, and PFAS — chemicals that accumulate in the body over time. And here’s the kicker: Shannon Fitzgerald, a toxicologist and pharmacist, has said that “residual concentrations” of these chemicals are continuously released from the fabric. Washing the garment doesn’t reduce exposure. Wearing it doesn’t reduce exposure. The chemicals just keep coming.
The “Cotton Gusset” Trick That Doesn’t Actually Work
You’ve probably noticed that even synthetic underwear usually has a small cotton panel sewn into the crotch area. That little strip is called the gusset, and most people assume it makes their polyester underwear safe. It doesn’t.
Cleveland Clinic OB-GYN Dr. Erica Newlin has addressed this directly: that small cotton panel doesn’t fully protect you from the surrounding synthetic fabric and won’t breathe like 100% cotton. The rest of the underwear is still trapping heat, still holding moisture, and still pressing synthetic chemicals against your skin. It’s the textile equivalent of putting a screen door on a submarine.
Dr. Newlin recommends cotton as the daily go-to because it’s less likely to cause allergic reactions and it actually wicks away excess sweat and moisture. If you have extra-sensitive skin, she suggests plain white cotton — no dyes, no frills. And yes, she says non-cotton underwear is fine to wear occasionally, but for regular daily wear, all-cotton wins.
A Brief History of How We Got Here
Synthetic fabrics were originally created in the 1930s to replace natural fabrics with stronger, lighter, and cheaper versions. That economic incentive hasn’t changed. Polyester is still dramatically cheaper to produce than cotton, which is why brands from Hanes to Victoria’s Secret rely heavily on synthetic blends.
One of the first red flags came back in 1984, when researchers evaluated over 24,000 workers in a textile factory that produced synthetic fabrics. They followed the workers for 14 years and found that those handling synthetics had a higher incidence of colorectal cancer. Later research at the University of Birmingham showed that when you sweat, your body’s natural oils can actually dissolve the plastics in synthetic materials — pulling chemicals directly into your skin.
What Doctors Actually Want You To Buy
The advice from the medical community is surprisingly unanimous and refreshingly simple. Cotton. Just buy cotton.
Dr. Suzy Lipinski, a board-certified OB-GYN at Pediatrix Medical Group in Denver, also recommends hemp, bamboo, and linen as solid alternatives. Bamboo in particular is growing in popularity because it’s gentle on sensitive skin and naturally breathable. Cotton stands out because it’s comfortable, cool, moisture-wicking, and absorbent — though those qualities vary based on the quality of the fiber and the weave.
Organic cotton is even better, since it’s grown without synthetic pesticides and herbicides and is naturally hypoallergenic. If you’re someone who deals with recurring infections or irritation, it might be worth the slight price bump.
A few other tips doctors agree on: change your underwear at least once a day. If you’ve been sweating heavily from a workout or hot weather, swap to a fresh pair. Wash new underwear before wearing it — this removes chemicals left over from manufacturing, storage, and transport. Use hypoallergenic, fragrance-free detergent, and consider running a double rinse cycle. Some doctors even recommend going commando at night to let things air out, especially if you’re dealing with a yeast infection or vulvar irritation.
Most gynecologists and hygiene experts also suggest replacing your underwear every six months to a year. Old underwear can harbor bacteria that washing — especially cold water cycles — doesn’t fully eliminate.
Look, nobody wants to think this hard about underwear. But you’re wearing it for roughly 16 to 24 hours a day, against one of the most absorbent and sensitive parts of your body. The fabric you choose is one of those small decisions that quietly shapes your health — and right now, most of us are getting it wrong.
