Synthetic Underwear, Microplastics & Male Fertility: The Connection

Last updated: May 25, 2026

Why underwear matters more than other clothing

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

1. Contact time. Most people wear underwear 16+ hours a day, every day. The only longer-contact garment is bedding.
2. Contact location. Direct skin contact on the genital and perineal area, where the skin is thinner and more permeable than skin elsewhere.
3. 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

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:

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

See related: microplastics in semen, microplastics in clothing, and microplastics and skin absorption.