Synthetic Underwear, Microplastics & Male Fertility: The Connection

MicroPlastics Research DeskEditorial team

November 1, 2025

9 min read

Last reviewed: May 25, 2026 by the MicroPlastics Research Desk. Submit a correction or see our editorial standards.

Quick Answer

Polyester, nylon, and synthetic-blend underwear sit in continuous contact with reproductive-zone skin for 16+ hours a day, releasing microfibres and plasticisers into a region with high blood flow and sensitive temperature regulation. A 1993 Egyptian study by Shafik found polyester underwear reduced sperm count and quality in male dogs and humans, attributing the effect partly to electrostatic interference. The 2024 microplastics-in-semen studies (Hu, Zhao, Montano) add a new dimension, synthetic underwear is one of the most direct skin-contact sources. The solution: 100% cotton, organic cotton, merino wool, or hemp underwear for anyone trying to conceive or concerned about fertility.

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Synthetic underwear, microplastics and male fertility

Key Takeaways

Polyester / nylon underwear is continuous skin contact for 16+ hours/day directly on reproductive-zone skin.
Shafik 1993 study: polyester underwear in male dogs caused reduced sperm count + atrophy after 2-12 months. Effect reversed after switching to cotton.
2024 microplastic-in-semen studies (Hu, Zhao, Montano) found PET in 100% of human semen samples, polyester underwear is a plausible direct source.
Synthetic fabrics also release brominated flame retardants and plasticisers absorbed through skin.
Best alternatives: 100% organic cotton (Pact, Boody, Cottonique), merino wool (Wool&Prince, Smartwool), hemp (Hempys, WAMA).

Why underwear matters more than other clothing

Three factors make underwear uniquely high-risk for microplastic and chemical exposure:

Contact time. Most people wear underwear 16+ hours a day, every day. The only longer-contact garment is bedding.
Contact location. Direct skin contact on the genital and perineal area, where the skin is thinner and more permeable than skin elsewhere.
Movement and sweat. Friction increases fibre release; sweat acts as a solvent for plasticisers and brominated flame retardants.

The 1993 Shafik study

Ahmed Shafik at Cairo University published a series of studies between 1992 and 1993 examining the effect of polyester underwear on male reproductive function. Key findings:

In male dogs: 12 months of polyester underwear use caused reduced sperm count and testicular atrophy compared to cotton-wearing controls.
The effect was partly attributed to electrostatic charge from polyester fibres interfering with the reproductive system.
Effects reversed within months after dogs switched back to cotton.
Parallel observational data in men showed similar patterns.

The Shafik studies were small and the methodology has been questioned. But they sparked decades of interest in the question of whether synthetic intimate-wear affects fertility.

Combine with the 2024 microplastic-in-semen findings

The 2024 studies on microplastics in human semen (Hu et al., Zhao et al., Montano et al.) added a major data point. They found:

PET (polyethylene terephthalate) in 100% of human semen samples tested across multiple countries.
PET is the dominant polymer used in polyester clothing, including underwear.
Polypropylene and PVC were also detected.
Higher particle counts correlated with reduced sperm motility.

The studies don't identify underwear as the source, but given the extreme contact time on reproductive-zone skin, it's a biologically plausible major contributor. See our microplastics in semen article for the full study breakdown.

Underwear materials compared

Underwear materials ranked for microplastic and fertility-relevant exposure
Material	Microplastic safety	Notes
100% organic cotton	Lowest exposure	Best balance of safety, comfort, breathability
Standard cotton (non-organic)	Low	Cotton itself is plastic-free; may have pesticide residues from cultivation
Merino wool	Low	Natural antimicrobial; temperature-regulating; expensive
Hemp	Low	Plant fiber; durable; less common
Linen	Low	Plant fiber; cool; less commonly available as underwear
TENCEL™ Lyocell	Low (semi-synthetic from wood pulp)	Closed-loop processing; probably safer than viscose
Bamboo viscose	Low-moderate (semi-synthetic)	Processed with chemicals but plant-derived
Modal	Low-moderate (semi-synthetic)	Similar to viscose; wood-derived
Cotton-spandex blend	Moderate	5-10% spandex/elastane is plastic; rest cotton
Polyester / nylon	Higher exposure	Synthetic microfibre shedding + electrostatic effects (Shafik 1993)
Polyester satin / silk-look	Higher exposure	Most "silky" or "performance" underwear
Microfibre / "moisture-wicking" performance underwear	Highest exposure	Pure synthetic; designed for friction

Recommended natural-fibre underwear brands

Pact Apparel. Fair Trade certified organic cotton; widely available for men and women. $14-22.
Boody Bamboo Viscose, soft, OEKO-TEX certified; semi-synthetic but plant-derived. $12-22.
Cottonique 100% Organic Cotton, hypoallergenic; latex-free elastic alternatives for sensitive skin. $18-28.
WAMA Hemp Underwear. 100% hemp + organic cotton blends. $20-30.
Wool & Prince Merino Boxers, premium merino; expensive but long-lasting. $35-55.
Cosabella Organic Cotton. Italian-made organic cotton intimates. $30-50.
Calida Switzerland 100% Cotton. Swiss-made fully natural cotton. $25-45.
Hanes 100% Cotton Classic, basic mainstream pure cotton option. $10-15.

Special focus: trying-to-conceive (TTC) for men

Men trying to conceive should consider this one of the higher-impact fertility changes:

Switch all underwear to 100% organic cotton. Make the change at least 90 days before conception attempts (sperm regeneration cycle).
Switch sleepwear to natural fibers for the 8-hour nightly contact period.
Switch synthetic activewear, performance polyester is friction-heavy + sweat-heavy + close-contact.
Switch tight-fitting synthetic gym shorts for cotton or merino wool athletic shorts.
Pair with broader microplastic reduction, see our microplastics and fertility and preconception guides.

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Frequently Asked Questions

Does polyester underwear cause infertility?

A 1993 series of studies by Shafik at Cairo University found polyester underwear reduced sperm count and caused testicular atrophy in male dogs after 12 months, with similar patterns in observational human data. Effects reversed after switching to cotton. The 2024 microplastic-in-semen studies add new mechanistic plausibility.

What underwear is best for fertility?

100% organic cotton is the safest mainstream option. Merino wool (Wool & Prince), hemp (WAMA), and 100% standard cotton (Hanes Classic) are all evidence-supported. Avoid polyester, nylon, microfiber, and "performance" or "moisture-wicking" synthetic underwear when trying to conceive.

How long does it take to see fertility improvement from switching underwear?

Sperm regenerate on a ~72-90 day cycle. Switching underwear at least 90 days before conception attempts allows a full new sperm generation under reduced-exposure conditions. Combine with broader microplastic reduction (filtered water, no plastic food storage, etc.) for maximum effect.

Is bamboo viscose underwear safe?

Bamboo viscose is semi-synthetic, plant-derived but chemically processed. It is dramatically safer than polyester/nylon but slightly less clean than 100% cotton or wool. OEKO-TEX certified bamboo viscose (Boody) is a reasonable middle option.

Does spandex / elastane in underwear matter?

Cotton-spandex blends (5-10% spandex) are commonly used for stretch. The spandex is plastic but the predominant cotton dominates the fabric chemistry. This is significantly better than full-synthetic underwear. For maximum reduction, look for natural-rubber waistband alternatives (Cottonique, Pact organic).

What about underwear during pregnancy or breastfeeding?

The same principles apply, synthetic fabrics shed fibers and chemicals into close-contact skin. For pregnancy and breastfeeding, prioritize 100% organic cotton next-to-skin. See our microplastics in pregnancy by trimester guide.

Sources

Shafik A (1993). Effect of different types of textiles on male sexual activity. European Urology.
Hu CJ, Garcia MA, Nihart A, et al. (2024). Microplastic presence in dog and human testis and its potential association with sperm count. Toxicological Sciences.
Zhao Q, Zhu L, Weng J, et al. (2024). Detection and characterization of microplastics in the human testis and semen. Science of the Total Environment.
Levine H, Jørgensen N, Martino-Andrade A, et al. (2023). Temporal trends in sperm count: a systematic review and meta-regression analysis. Human Reproduction Update.

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