Researchers in 2024 found microplastics in every human semen sample they tested in a multi-site Chinese cohort (Zhang et al., eBioMedicine, 2024). A separate meta-analysis in Human Reproduction Update reported that average sperm concentration fell from about 101 million per milliliter in 1973 to 49 million per milliliter in 2018 (Levine et al., 2023). The environment is not a side note in male fertility. It is part of the daily exposure load.
Heat from a warming climate reaches the testicles
The testicles sit outside the body for a reason. Sperm production runs best when scrotal temperature stays a few degrees below core body temperature. The cremaster muscle raises and lowers the testicles to manage that gap. The skin on the scrotum also sweats to shed heat. When outside heat overwhelms those systems, sperm parameters fall.
Sauna-level heat temporarily lowers sperm count and can worsen morphology (Garolla et al., Human Reproduction, 2013). The effect reverses once the heat exposure stops. A 2007 study in Fertility and Sterility found the same recovery pattern after men stopped regular wet heat exposure (Shefi et al., 2007). Short-term heat is real but not permanent.
Climate change extends the problem in time. Hotter summers and longer heat waves increase the number of hours the scrotum has to work against outside heat. Men who work outdoors in hot climates get a heavier dose of this heat load. A laptop resting on the lap can raise scrotal temperature enough to matter (Sheynkin et al., Human Reproduction, 2005). Tight underwear does something similar. Men who reported looser, boxer-style underwear had higher sperm concentration and total count in a fertility-center cohort (Minguez-Alarcon et al., Human Reproduction, 2018). Heat is cumulative. More hours per day means more exposure.
Whether regular heat exposure shifts circulating testosterone long term is not settled by large trials. Heat stresses the temperature-sensitive cells. A single session does not crash testosterone. The acute, reversible effect on sperm parameters is the settled part.
Air pollution and oxidative stress
Air pollution reaches the testicles through the bloodstream. Fine particles carry metals and polycyclic aromatic hydrocarbons, which can trigger oxidative stress in developing sperm. Oxidative stress is a form of cell damage that affects sperm DNA and membrane integrity. A 2021 review in Frontiers in Endocrinology summarized how environmental chemicals, including airborne pollutants and phthalates, interfere with male reproductive hormones and sperm production as a group (Rodprasert, Toppari, and Virtanen, 2021). Men are rarely exposed to one chemical at a time, so the combined burden matters more than any single source.
Endocrine disruptors from plastics and pesticides
Phthalates and bisphenols are plasticizers used in food packaging, fragrances, and personal care products. They mimic or interfere with hormone signaling. A 2024 meta-analysis in Toxics pooled human studies and found that higher BPA exposure was associated with lower sperm concentration and motility (Lu et al., 2024). The evidence is observational, not experimental, but the direction is consistent. Pesticide exposure can affect the same endocrine pathways. The body clears some of these compounds through the liver and kidneys, but daily re-exposure keeps the load present.
Microplastics in the reproductive tract
Microplastics have now been detected inside male reproductive tissue. Zhao and colleagues reported this in Science of the Total Environment in 2023, and Li and colleagues confirmed it in 2024. One study found microplastics in all semen and urine samples it tested and linked mixed exposure to poorer sperm parameters in statistical models (Zhang et al., eBioMedicine, 2024). Another found microplastics in human and dog testes and reported an association with sperm count (Hu et al., Toxicological Sciences, 2024).
Presence is established. Whether that presence causes harm is still open. None of these studies proves microplastics cause lower fertility in humans. None traces the particles in tissue back to clothing. They may come from food, water, air, or all three. The measured statement is that reproductive tissue is no longer shielded from plastic exposure.
Reducing the controllable exposures
The largest controllable exposures are heat, plastic food contact, and the underwear you wear all day. You can reduce those without overhauling your life.
- If you are trying to conceive, limit wet heat exposure like hot tubs and saunas, and avoid resting a laptop directly on your lap.
- Choose underwear that lets air move. A relaxed fit with breathable fabric keeps the area closer to the temperature it prefers than tight, heat-trapping underwear does. That describes airflow and temperature, nothing more.
- Reduce plastic food contact. Store hot food in glass or stainless steel. Do not microwave plastic. Filter drinking water if microplastics are a concern.
- Wash produce to remove surface pesticide residue. Buying organic reduces some pesticide exposure but does not change the packaging.
- Eat zinc-rich foods. Oysters, pumpkin seeds, beef, and beans contain zinc, which is involved in normal sperm production. Keep this at the food level.
If you are trying to conceive, a reproductive urologist can order a semen analysis. That gives you a baseline and takes the guesswork out of the conversation.
What the evidence does not settle
Several gaps remain. No study measures microplastic shedding from worn underwear under sauna heat and sweat. No study attributes the microplastics found in human tissue to clothing versus other sources. The long-term effect of chronic mild scrotal heat from everyday clothing or regular sauna on circulating testosterone in humans is unsettled. The acute, reversible effect on sperm parameters is the part that is well characterized.
This content is for educational purposes only and is not medical advice. Oakman products are designed for physical comfort and cooling; they make no claims about fertility, sperm quality, or hormone levels. Consult a healthcare professional for personalized advice.