Search for the best underwear for sperm health and most guides hand you the same two-option answer: boxers or briefs. A 2018 study of men at a fertility center found higher sperm concentration and total count among those who reported wearing mostly boxer-style underwear compared to tighter styles (Minguez-Alarcon et al., Human Reproduction, 2018). That result gets quoted constantly. It also stops the conversation a step too early.
What gets left out is that fabric and fit change the environment around the testicles in ways the boxers-versus-briefs framing never touches. The research has moved on. If you are trying to keep that area cooler and cleaner, the relevant questions are what the fabric does with heat and moisture, and what the fabric is made of.
The testicles run on a narrow thermal budget
Sperm production works best a few degrees below core body temperature. A 2013 study in Human Reproduction reported that sauna-level heat temporarily lowered sperm count and worsened morphology, with the effect reversing once heat exposure stopped (Garolla et al., Human Reproduction, 2013). A separate study of men who stopped regular wet heat exposure found semen parameters recovered over time (Shefi et al., Fertility and Sterility, 2007).
Underwear is not a sauna. The point is that small daily heat sources stack. Tight underwear and long sitting both raise scrotal temperature. A 2005 study found sitting raised scrotal temperature compared with walking, and tighter underwear raised it further (Jung et al., Human Reproduction, 2005). Another study measured scrotal temperature rising during laptop use with the computer on the lap (Sheynkin et al., Human Reproduction, 2005).
None of this proves a specific pair of underwear causes infertility. It shows that fit and daily habits change local temperature, and local temperature matters for sperm production.
Scrotal skin is more absorbent than most of your body
The skin on the scrotum responds to more than heat. It is one of the most permeable patches of skin on the body. A 1971 human absorption study dosed different body sites with the same compound and found scrotal penetration far above the forearm baseline, near the top of the range across tested sites (Maibach et al., Archives of Environmental Health, 1971). The anatomy explains why. Thinner outer skin layer, more follicles, more blood supply.
Heat and damp increase that uptake. A 2020 ex-vivo study found raising skin temperature from 25 to 39 degrees Celsius increased absorption of test compounds by more than 200 percent (Toxicology in Vitro, 2020). Earlier work showed occlusion and skin hydration also raise penetration (British Journal of Dermatology, 1988). Add those pieces together and you get a highly permeable area, covered, warm, and damp. That describes the inside of most men's underwear on an active day.
This is general dermatology. What is missing is a measured dose from modern underwear, and no study has quantified that. But the general finding puts material choice in the same conversation as fit.
Fabric chemistry does not always stay put
Most men assume fabric sits there inert. Standard test methods show otherwise. In a 2021 study using standardized artificial sweat, researchers measured trace antimony migrating out of polyester textiles (Regulatory Toxicology and Pharmacology, 2021). Polyester is made with an antimony catalyst, and a small fraction can mobilize into sweat. A 2016 textile study found residual formaldehyde from cotton finishes released into synthetic sweat (Textile Research Journal, 2016). The amounts are trace. The tests exist because fabric chemistry does not always stay bound to the fiber.
Synthetic garments also shed microfibers during ordinary wear, not only in the wash. A 2020 study measured polyester clothing releasing microfibers into the air as a person moved, at a magnitude in the same ballpark as laundering when scaled (De Falco et al., Environmental Science and Technology, 2020). Separately, researchers have detected microplastics in human testicular tissue and semen. One study using Raman methods found microplastics in every seminal fluid sample tested (Li et al., Science of the Total Environment, 2024). Another detected microplastics in human and dog testes (Hu et al., Toxicological Sciences, 2024).
None of these studies traced the particles to clothing. The human data show presence and association, not proven harm from underwear. That is an important line to hold.
Cotton, polyester, and what the fiber actually does
Fabric choice usually gets treated as a comfort argument. For the scrotal environment, the relevant distinction is what a fiber does with heat and moisture, and what it is made of.
Cotton absorbs moisture and holds it. Studies on moisture management show cotton stays damp longer than regenerated cellulosic or blended fabrics (Jhanji et al., Fashion and Textiles, 2015). In a hot room or after a workout, damp cotton pressed against the skin keeps the area warm and hydrated. Organic cotton does not change this. The organic label describes how the crop was grown, not how the fabric behaves in heat.
Polyester moves moisture faster than cotton, but it is plastic. That is the material that sheds microfibers during wear and can carry antimony residue. Conventional elastane and spandex are also polyurethane, a plastic. Most natural fiber underwear still runs a plastic thread through the waistband and legs for stretch.
Regenerated cellulose fibers such as modal and lyocell manage moisture and air movement well in controlled tests (Ozdemir, Journal of Engineered Fibers and Fabrics, 2017, and Kucukali-Ozturk et al., Fibers and Polymers, 2023). When a naturally derived fiber sheds, the shed material is biodegradable cellulose, not a persistent plastic microfiber. That distinction is the defensible one. It does not mean natural fibers shed less. Some bench tests show cellulosic knits shed as much or more fiber by mass as polyester. The point is what the fiber is.
What to look for if you want to keep things cool
No single underwear is the right choice for every man. The research points to a few physical features for men who want to keep that area closer to the temperature it prefers.
- Fit that lets air move. Relaxed boxer-style fits and gussets built for air movement allow more evaporation than tight briefs or compression shorts. The Minguez-Alarcon study found looser boxer-style underwear associated with higher sperm concentration and total count in a fertility-center cohort, an association, not a controlled experiment. Physical studies on scrotal temperature support the mechanism: looser fit and movement lower scrotal temperature (Jung et al., Human Reproduction, 2005, and Mieusset et al., Journal of Andrology, 2007).
- Fabric that manages moisture without being a persistent plastic. Modal and lyocell wick moisture and breathe better than cotton in controlled tests. The stretch component matters too because conventional elastane is plastic. One option built around these physical points is Oakman's boxer brief, which uses a relaxed non-constrictive fit with a gusset for airflow, siro-spun TENCEL MicroModal, and ROICA V550, a degradable elastane from Asahi Kasei. That is a material and cooling choice, not a fertility guarantee.
- Watch the daily heat stack. Laptop on the lap, long uninterrupted sitting, and tight synthetic briefs all push scrotal temperature in the same direction. If you use a sauna and want to keep the area cooler during a session, physical cooling during the heat exposure is the relevant move, not cooling afterward as if it undoes the exposure. Some men use a cold pack against the area during a sauna session and wear breathable fabric the rest of the day.
The useful move is to stop stacking avoidable heat and persistent plastic against a region that is temperature-sensitive and highly absorptive.
Where the evidence gets thin
This topic attracts overstatement, so the gaps matter. No study has measured microfiber shedding from worn underwear under sauna heat and sweat. No study has traced microplastics in human testes to clothing rather than other sources. The long-term effect of chronic mild scrotal heat from everyday clothing or regular sauna on circulating testosterone is unsettled. The well-characterized piece is the acute, reversible effect of heat on sperm parameters (Garolla et al., Human Reproduction, 2013, and Shefi et al., Fertility and Sterility, 2007). The microplastics and fertility human data are associations, not proven cause.
If a post or product tells you underwear will protect your sperm, that claim is not supported by the published research I have read. What is supported: local heat is measurable, skin permeability is real, fabric chemistry migration is documented, and fit changes scrotal temperature. Use those four facts to choose.
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.
Frequently asked questions
do boxers actually improve sperm health
A 2018 study of men at a fertility center found higher sperm concentration and total count among those who reported wearing mostly boxer-style underwear compared to tighter styles. That finding is an association, not a controlled experiment. Physical studies support the mechanism: looser fit and movement lower scrotal temperature, and sperm production likes a cooler environment.
what should I look for in underwear for sperm health
Look for a relaxed fit that lets air move instead of trapping heat, and fabric that manages moisture without being a persistent plastic. Modal and lyocell wick moisture and breathe better than cotton in controlled tests, and they shed biodegradable cellulose rather than plastic microfibers. Avoid stacking avoidable heat from tight briefs, laptop use, and long sitting.
does polyester underwear affect sperm health
Polyester moves moisture faster than cotton, but it is plastic. Studies have measured polyester shedding microfibers during wear and trace antimony migrating into artificial sweat. The link to sperm health in humans is not proven, but the material choice matters because scrotal skin is highly permeable and heat plus damp increases absorption.
can I wear a sauna suit and protect sperm health
No, a sauna suit does not protect sperm health. Sauna-level heat temporarily lowers sperm parameters, and the scrotum is one of the most permeable skin areas, so trapped heat and damp can increase absorption. If you use a sauna, keep the area cool during the session rather than trying to cool it down afterward.