Sperm motility is the measure of how well sperm can move and swim toward an egg, a critical factor in male fertility. Healthy sperm motility depends on a delicate balance of conditions including temperature, lifestyle and environmental exposures. Testicles operate optimally a few degrees Fahrenheit cooler than core body temperature, which is why the testicles sit outside the body [1]. Keeping the testicles cooler during heat exposure, through breathable fabric and active cooling, is an exposure you can easily control.
How Heat Affects Sperm Motility
Heat exposure raises scrotal temperature, which can impair sperm production and function. Leydig cells, which produce testosterone, and sperm cells are both highly sensitive to temperature. When scrotal temperature rises, the enzymes these cells rely on become less active, slowing sperm production and reducing motility [2].
Studies show that even moderate heat exposure, like prolonged sitting or wearing tight, non-breathable underwear, can raise scrotal temperature enough to affect sperm parameters. Sauna use, for example, has been shown to reduce sperm motility. The effect is reversible, but it reverses only once the heat exposure stops, not when you step out of the room. Men who used a sauna twice a week for three months were back to normal six months after they stopped [3].
Garment choice matters too. Tight, synthetic underwear traps heat and restricts airflow, raising scrotal temperature. Breathable, airflow-friendly fabrics let heat escape instead of trapping it against the skin, so scrotal temperature stays lower [5].
Other Factors That Influence Sperm Motility
Beyond heat, lifestyle and environmental factors also play a role. Bisphenol A, the plastic additive better known as BPA, has been linked to lower sperm counts [4]. Phthalates are a related group of plastic additives that turn up in the same everyday products. Stress, poor diet, and lack of exercise can further compound these effects.
Both are avoidable without much effort. Store food and pantry staples in glass rather than plastic, never microwave food in a plastic container, and skip plastic wrap on anything hot. Those three habits close most of the everyday routes into the body.
What You Can Do About It
While some factors like environmental exposures are harder to control, others are manageable. Choosing breathable, natural-fiber underwear helps keep scrotal temperature lower during daily activities. For heat exposure like sauna sessions, a removable cold pack worn during the session cools the testicles directly and offsets the rise in scrotal temperature.
How Oakman Helps
Oakman boxer briefs are designed to keep the testicles cooler during heat exposure, whether in daily life or during sauna sessions. The fabric is TENCEL-branded MicroModal, naturally derived from wood pulp, which breathes better than synthetic materials and doesn't shed microplastics like polyester underwear [6].
The removable cold pack, made of medical-grade nylon, sits in a front pocket with a layer of soft fabric between it and the skin. It cools the testicles directly during sauna sessions, keeping them nearer the temperature they work best at.
The athletic fit includes a gusset, an extra panel that gives the testicles room and airflow, so scrotal temperature stays lower than it would in tight, heat-trapping underwear. Together these features keep the testicles cooler than tight, heat-trapping underwear does.
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Frequently asked questions
Does underwear affect sperm motility?
Yes. Tight, non-breathable underwear can raise scrotal temperature, which may impair sperm motility. Breathable, airflow-friendly fabrics let heat escape rather than trapping it against the skin.
Can heat exposure permanently damage sperm motility?
Heat exposure reduces sperm motility. It is reversible, but recovery starts when the heat exposure stops rather than at the end of a session, and in the study that followed men afterwards it took six months.
What fabrics are best for keeping scrotal temperature lower?
Natural fibers like TENCEL-branded MicroModal breathe better than synthetics and help keep scrotal temperature lower.
How does sauna use affect sperm motility?
Sauna use temporarily raises scrotal temperature, which can reduce sperm motility. Active cooling during the session helps offset this effect.
This is for general educational and informational purposes only and is not medical advice. It makes no claim about fertility, sperm, or testosterone outcomes from any product. Always talk with a qualified healthcare provider before making changes to your diet, exercise, or health routine. These statements have not been evaluated by the Food and Drug Administration. Oakman products are apparel and are not intended to diagnose, treat, cure, or prevent any disease.
References
- Ivell R. (2007). Lifestyle impact and the biology of the human scrotum. Reproductive Biology and Endocrinology (BioMed Central). [Link]
- Durairajanayagam D, Agarwal A, Ong C. (2015). Causes, effects and molecular mechanisms of testicular heat stress. Reproductive BioMedicine Online. [Link]
- Garolla A, et al.. (2013). Seminal and molecular evidence that sauna exposure affects human spermatogenesis. Human Reproduction. [Link]
- Lu L, Liu Y, Yang Y, He J, Luo L, Chen S, Xing H. (2024). Bisphenol A Exposure Interferes with Reproductive Hormones and Decreases Sperm Counts: A Systematic Review and Meta-Analysis of Epidemiological Studies. Toxics (MDPI). [Link]
- Jung A, Leonhardt F, Schill W-B, Schuppe H-C. (2005). Influence of the type of undertrousers and physical activity on scrotal temperature. Human Reproduction (Oxford University Press). [Link]
- Napper IE, Thompson RC. (2016). Release of synthetic microplastic plastic fibres from domestic washing machines: Effects of fabric type and washing conditions. Marine Pollution Bulletin (Elsevier). [Link]
