Polyester: the Birth Control You Didn’t Sign Up For
Wearing activewear (polyester) daily? It might be silently disrupting your hormones.
Leggings. Sports Bras. Underwear. Activewear. We’re basically wrapped in plastic… and science is sounding the alarm.
recent studies
In one study - pregnant dogs wore different fabric garments. Only those in 100% polyester showed low progesterone (a key pregnancy hormone) and miscarriage. When they wore natural fibres again, hormones normalised and they conceived healthy pups. It wasn’t random - it was polyester.
Another study showed male dogs wore polyester pants for 24 months. The result included significant drop in sperm count, more abnormal sperm and testicular damage.
Once polyester was removed, 10 out of 12 recovered. But 2 remained infertile. The damage isn’t always reversible.
A clinical human study had 14 men wear a polyester sling on their scrotum for 12 months. All 14 became infertile. Zero sperm. Shrinking testicles. No pregnancies. Once the sling was removed, fertility returned. Synthetic fabrics directly impacted sperm production.
Researchers believe this was due to:
Disrupted temperature regulation
Electrostatic charges from polyester
This next one shocked us - microplastics were found in human ovarian follicular fluid. It was found in 14 of 18 women undergoing IVF, particles were small enough to enter the bloodstream, reaching the ovaries and granulosa cells (which nurture your eggs). This is also linked to changes in FSH — a hormone tied to fertility struggles.
Plastic isn’t just “around” us anymore. It’s in us.
what do polyester, spandex, and nylon all have in common?
They’re synthetic, plastic-based, and worn close to our most sensitive hormonal centers. Your skin absorbs more than you think — especially in high-sweat, high-friction areas.
These materials:
trap heat
create electrostatic friction
shed microplastics
can release BPA, a known endocrine disruptor
findings from mainstream brands
A 2023 report from the Center for Environmental Health (CEH) found that multiple mainstream brands of sports bras and leggings exposed wearers to up to 40x the safe BPA limit!
In a 2022 investigation, 63% of tested sports bras and athletic leggings from major brands contained detectable levels of PFAS (associated with potential hormone imbalance, gut issues, fertility struggles, and more).
This needs to become a more widely discussed. public health conversation.
could htis be a missing puzzle piece?
If you’re actively healing your hormones — working on fertility, PCOS, thyroid, metabolism, or period pain — this isn’t something you should discount addressing. It could be the missing piece of the puzzle.
Our clothes are part of our internal environment, and your environment plays a direct role in hormonal balance.
best plastic-free fibers
brands that tested positive for organic fluorine (a marker for PFAS chemicals)
Nike
Patagonia
The North Face
New Balance
Athleta
Champion
Asics
Adidas
Fablectics
FILA
Reebok
Gaiam
Lululemon
Align
Mizuno
LulaRoe
Old Navy
OYA
Femtech
Vuori Yogalicious
* found from Mamavation’s 2023 testing on yoga pants + leggings
