Boxers, Cycling, and Cooling Gadgets: What You Can Stop Worrying About

Evidence-based · Written by Dr. Lejla Fazlicic, D.Ac, L.Ac · All key claims cited to peer-reviewed research

The short answer: Boxers or briefs? It is one of several widely repeated pieces of male fertility advice rest on evidence that is thinner than the advice sounds. Underwear type has been directly tested for its supposed temperature mechanism and no temperature difference was found. Measured scrotal temperature during moderate cycling is lower than during quiet sitting. Laptop cooling pads failed in the one study that tested them, and scrotal cooling devices have never been tested in a trial worth acting on. None of this means heat is irrelevant, and it is not a claim that anything you have already done was wrong. It means the list of things worth your attention is shorter than the internet suggests.

Start With the List, Not the Worry

Most fertility advice works by addition. Every article hands you one more thing to monitor, and each one arrives with the same implied weight as all the others, so the list grows and nothing ever leaves it. By the time a couple reaches a first or second IVF cycle, that list can run to twenty items, most of them unranked and several of them contradictory.

This article does the opposite. It goes through the heat advice that circulates most widely and asks a plain question of each item: when researchers actually went and measured this, what did they find. In several cases the honest answer is that the proposed mechanism was tested directly and did not appear. That is a useful finding, not a disappointing one, because it lets you take the item off the list.

One framing point before the detail, and it applies to nearly everything below. Almost all of these studies measured semen parameters, not pregnancy and not live birth. A study can show a difference in sperm concentration between two groups of men and still tell you nothing about whether either group had more babies. Where a study did look at pregnancy and live birth, it is flagged, because those are rare and they matter more.

If you want the underlying biology first, the pillar article on how heat affects sperm covers what temperature does to sperm production and over what timescale. This piece assumes that groundwork and goes after the specific claims.

Boxers or Briefs: Does Underwear Type Affect Fertility?

This is the single most repeated piece of male fertility advice in existence, and it is the one with the most interesting evidence trail, because the evidence points in two directions at once.

The strongest study in favour is a 2018 cross-sectional analysis of 656 male partners attending a fertility centre. Fifty-three percent usually wore boxers. Those men had 25% higher sperm concentration (95% CI 7% to 31%), 17% higher total sperm count (95% CI 0% to 28%), 33% higher total motile sperm count (95% CI 5% to 41%), and 14% lower serum FSH (95% CI −27% to −1%).¹ The concentration finding is the headline, and it is a real difference in a reasonably large sample. Three things temper it. The total-count estimate was modest and borderline, with a 95% confidence interval from 0% to 28%. There was no association with morphology or sperm DNA damage. And the design is cross-sectional with self-reported underwear in a fertility-clinic population, so it can describe an association but cannot show that changing underwear changes anything. No pregnancy or fertility outcome was measured.

Now the part that rarely gets quoted. The entire rationale for the advice is thermal: briefs hold the testicles closer to the body, therefore briefs run hotter. In 1998 researchers measured that directly in 97 consecutive subfertile men, recording scrotal, core, and skin temperatures. Mean scrotal temperature was 33.8 ± 0.8 °C in boxer wearers and 33.6 ± 1.1 °C in brief wearers, which is not a significant difference. There was no difference in the core-to-scrotal gradient and no difference in semen parameters. A separate crossover arm, in which 14 men switched underwear type and were remeasured, found the same.² The authors' conclusion was unusually direct: "Routinely advising infertility patients to wear boxer shorts cannot be supported by available scientific evidence."

Hold those two studies next to each other. One found a difference in sperm concentration between boxer wearers and brief wearers. The other went looking for the temperature difference that was supposed to cause it and did not find one. That does not make the 2018 result wrong, but it does mean the mechanism everyone assumes is doing the work has been tested and did not show up. Something else may explain the association, including the possibility that men who wear boxers differ from men who wear briefs in ways that have nothing to do with their scrotal temperature.

The largest UK study sits in between. CHAPS-UK compared 939 men with low motile sperm concentration against 1,310 referents across 14 fertility clinics, and found boxer shorts protective, with an odds ratio of 0.76 (95% CI 0.64 to 0.92).³ A real signal, and a small one. What is more striking is what the authors concluded from their own full dataset of lifestyle factors: "Common lifestyle choices make little contribution to the risk of low MSC," and "delaying assisted conception to make changes to lifestyle is unlikely to enhance conception." That second sentence was written by researchers who had just found a statistically significant underwear effect, and it is the sentence worth carrying with you.

A 2026 narrative review of the whole area lands in the same place: "Underwear choice has been variably associated with modest differences in sperm production parameters, although findings are inconsistent and clinical fertility outcomes have not demonstrated clear associations... underwear choice alone is unlikely to meaningfully influence fertility outcomes for men."⁴ The same review notes that evidence on fabric composition remains limited and that controlled comparisons are lacking, so if anyone has told you cotton versus synthetic matters, there is no body of research behind it.

The practical verdict. Switching to boxers is free, harmless, and takes no effort. If he prefers them, or if doing it settles something for the two of you, do it. What it does not deserve is a place on a list of things to feel anxious about, and it is certainly not worth delaying a cycle for.

Does Cycling Affect Sperm Quality?

Here the evidence contains a genuine surprise, and it runs against the intuition almost everyone has.

In a standardised laboratory study, 25 men cycled for 60 minutes at 25 W in a 22 °C room while scrotal temperature was measured continuously. The saddle surface reached 35.59 °C, which is warm. Scrotal temperature barely moved, going from 35.75 to 35.82 °C on the left side. More interesting still, scrotal temperature during cycling was significantly lower than during the ten minutes of sitting that preceded it, by 1.31 °C on the left and 1.46 °C on the right, with p < 0.001.⁵ The likely explanation is airflow: pedalling moves air across the groin in a way that sitting still does not. The authors concluded that "moderate cycling... is not a major genital heat stress factor."

Read the caveats honestly, because they are real. Twenty-five watts is light effort, the session was an hour, and it was indoors under controlled conditions. This study says nothing about a four-hour road ride in summer, and nothing about saddle pressure, which is a separate non-thermal mechanism involving perineal compression rather than temperature.

Two larger observational studies found signals at high volume. In 2,261 men providing 4,565 semen samples, regular exercise overall was not materially associated with any semen parameter, but bicycling for five or more hours per week was associated with low sperm concentration (OR 1.92, 95% CI 1.03 to 3.56) and low total motile sperm (OR 2.05, 95% CI 1.19 to 3.56).⁶ Note the threshold. Five hours a week is committed cycling, not a commute. Note also the wide confidence intervals, the self-reported activity, and the fact that the mechanism was never identified, so pressure is at least as plausible as heat.

The most important study in this whole article is the one that measured what people actually want to know. In the EARTH cohort, 231 men provided 433 semen samples, and 163 couples went through 421 IVF or IUI cycles. Bicycling for 1.5 or more hours per week was associated with 34% lower sperm concentration (95% CI 4, 55%), P for trend 0.05. And then the finding that almost never gets repeated: "Paternal physical and sedentary activities were not related to clinical pregnancy or live birth rates following infertility treatment."⁷

That is the shape of this entire field in one study. A measurable difference appeared in the semen parameter, and it did not carry through to clinical pregnancy or live birth. Semen concentration is a proxy. It is a useful proxy, and it is not the outcome you are trying to reach.

The practical verdict. If he cycles a few hours a week and enjoys it, the honest position is that one cohort saw a signal from 1.5 hours a week and another only from five, both with wide confidence intervals, no identified mechanism, and no effect on clinical pregnancy or live birth. That is not a strong enough basis to give it up, and exercise has value that has nothing to do with sperm. For someone training at very high volume who wants to modify one variable, a temporary reduction is a reasonable personal choice. It is not a proven way to improve semen measures, pregnancy, or live-birth outcomes. If saddle discomfort or numbness is part of the picture, that is a fitting and pressure question for a bike fitter, and any persistent symptom belongs with his doctor.

Do Scrotal Cooling Devices and Laptop Cooling Pads Work?

These are the products marketed directly at couples preparing for treatment, often at meaningful cost, and they are where the evidence is weakest relative to the confidence of the marketing.

On scrotal cooling devices, the relevant document is a systematic review of eight studies, whose literature search closed in 2010. Its conclusion is worth quoting in full: "There was insufficient evidence to draw any firm conclusions about the impact of scrotal cooling on male fertility. A positive trend of improved male fertility was however observed. There is therefore a need for well designed randomised controlled trials."⁸ That is a fair summary of an unresolved question, and it is not a basis for spending money. A positive trend across eight heterogeneous studies is a reason to run a trial, not a reason to buy a device.

Laptop cooling pads have been tested more specifically, and the result is cleaner. Researchers measured scrotal temperature in 29 men using laptops in different configurations. Their stated conclusion was: "Scrotal shielding with a lap pad does not protect from scrotal temperature elevation."⁹ Only two things reduced the rise: sitting with the legs apart, and shorter sessions. The pad, which is the thing people buy, did not do the job it is sold to do. The laptop and driving question is covered properly in its own article in this cluster, so the point here is narrower, that the accessory sold as the solution has been tested and did not work.

Does Laptop Wi-Fi Damage Sperm?

This claim has an unusually traceable origin. In 2012, researchers took aliquots of sperm, placed them in petri dishes under a laptop connected to Wi-Fi, and left them for four hours.¹⁰ They reported reduced motility and increased DNA fragmentation, and the finding travelled around the internet at speed.

Two things about it. First, it is an ex vivo study, meaning sperm in a dish, not sperm in a man. Sperm in a dish have no scrotum, no blood supply, no thermoregulation, and none of the antioxidant environment of seminal plasma. Second, the paper drew two published rebuttal letters challenging its methods and interpretation, which is a strong signal of contested findings.

It is also not a heat study, despite being filed under heat advice almost everywhere it appears. There is no reliable in vivo human evidence that laptop Wi-Fi affects a man's sperm. This experiment does not provide a reliable basis for advice about Wi-Fi use, laptop placement, or fertility in living people.

Seven Claims, Side by Side

Look down the middle column. In every row except the last two, the proposed effect either failed to appear when measured directly, or appeared only as an association with no outcome behind it. And in the two rows that do carry weight, the studies are small and they measured semen, not babies.

Do Any Guidelines Recommend Boxers or Avoiding Heat?

No. Neither of the two major English-language guidelines tells men to change their underwear or avoid heat in order to improve fertility, and the reasons they give are instructive.

The AUA and ASRM position is not that heat has been ruled out. It is that when they searched for systematic reviews of sufficient quality on heat exposure and on underwear type, none met their inclusion criteria. There was not enough to work with. A guideline that stays silent where the evidence is thin is doing its job.

What Is Worth Attention, and What You Can Put Down

Here is the shorter list, which is the point of the article.

Worth some attention. Repeated, deliberate, intense heat — regular sauna sessions several times a week — produced reversible changes in a small sauna study, with complete reversal by six months after stopping.¹¹ Hot tubs are usually filed alongside saunas, but the one large cohort that measured hot baths and hot tubs against conception found no clear signal, with a confidence interval that included no effect at all.¹⁵ Pausing it during preparation is cheap and reversible. Genuine occupational heat, where a working day involves sustained high scrotal temperature, is the other one with a plausible signal behind it.¹² Both are covered in more depth in the article on saunas, hot tubs and fever.

What you can put down. Underwear type as a source of anxiety. Ordinary cycling. Laptop cooling pads. Wi-Fi. Scrotal cooling devices, at least until there is a trial worth reading. Fabric composition, on which the evidence is limited and the controlled comparisons have not been done.⁴ None of these has earned a place on a list you check at two in the morning.

One more thing worth saying plainly. If he made none of these changes, that is not something to look back on with regret, because no study has shown that any of them changes an outcome. The largest cohort to measure conception directly against heat exposures — 3,041 couples, including tight-fitting underwear, laptop hours and time spent sitting — found little association with any of them¹⁵. That is not reassurance offered to be kind. It is what the studies show, including the one study here that followed couples all the way to clinical pregnancy and live birth and found no relationship with paternal physical activity.⁷

If you want a preparation window that is actually anchored in biology rather than in accumulated worry, the piece on what one full sperm production cycle can and cannot change sets out the realistic timeframe. And any decision about treatment timing, medication, or a semen analysis result belongs with your reproductive endocrinologist or urologist, not with an article.

Related reading

• How heat affects sperm — the pillar article on the underlying biology and timescale.
• Saunas, hot tubs and fever: what the studies measured — the exposures that do have a measurable effect.
• How to lower sperm DNA fragmentation across one full sperm cycle — what the two-to-three-month window is actually for.
• Sperm DNA fragmentation testing: cost, methods and how to read the result — before you assume a number means something.

Frequently Asked Questions

Should my partner switch from briefs to boxers?

Only if he wants to. One cross-sectional study of 656 men found 25 percent higher sperm concentration in boxer wearers, but no difference in percent motility, morphology or sperm DNA damage, and it measured no pregnancy outcome. A separate study measured scrotal temperature directly in 97 men and found no meaningful difference between boxers and briefs, which undercuts the mechanism the advice is built on. NICE states that it is uncertain whether wearing loose-fitting underwear improves fertility. Switching is simple, so it is a reasonable thing to do, and it is not something that deserves worry.

Does cycling lower sperm count?

Not through heat, on the available measurements. In a controlled laboratory study, scrotal temperature during 60 minutes of moderate cycling was significantly lower than during the sitting that came before it, by roughly 1.3 to 1.5 degrees Celsius, probably because of airflow. Two larger observational studies did find associations with lower sperm concentration, but at reported cycling levels of 1.5 hours per week or more in one fertility-treatment cohort and five hours per week or more in another study. These were associations, not established thresholds, and neither study identified heat as the mechanism; saddle pressure is as plausible as temperature. Most importantly, the one study that followed couples through IVF and IUI found that paternal physical activity was not related to clinical pregnancy or live birth rates.

Do scrotal cooling devices work?

There is not enough evidence to say. A systematic review of eight studies concluded that there was insufficient evidence to draw any firm conclusions about the impact of scrotal cooling on male fertility, noted a positive trend, and called for well designed randomised controlled trials. That is an open research question rather than a product recommendation, and no fertility guideline recommends these devices.

Does laptop Wi-Fi damage sperm?

There is no reliable evidence that it does in a living person. The claim traces to a single 2012 study in which sperm samples in petri dishes were placed under a Wi-Fi connected laptop for four hours, and that paper drew two published rebuttal letters. Sperm in a dish have no thermoregulation, no blood supply and none of the protective environment they have in the body, so the finding does not transfer. It is also not a heat study, despite usually being filed as one.

Which heat exposures are actually worth avoiding before IVF?

Two are worth some attention. The first is repeated deliberate intense heat, such as regular sauna use, where a small study found measurable falls in count, motility and chromatin quality that fully reversed six months after the sessions stopped, with total sperm count still reduced at three months. The second is genuine occupational or sustained daily heat, where men with sustained scrotal temperatures above 35 degrees Celsius had markedly lower median sperm concentration. Both findings come from small studies that measured semen parameters rather than pregnancy or live birth, so hold them lightly, and raise any specific concern with your reproductive endocrinologist or urologist.

References

1. Mínguez-Alarcón L, et al. Type of underwear worn and markers of testicular function among men attending a fertility center. Hum Reprod. 2018;33(9):1749–56. https://doi.org/10.1093/humrep/dey259
2. Munkelwitz R, Gilbert BR. Are boxer shorts really better? A critical analysis of the role of underwear type in male subfertility. J Urol. 1998;160(4):1329–33. https://pubmed.ncbi.nlm.nih.gov/9751347/
3. Povey AC, et al. Modifiable and non-modifiable risk factors for poor semen quality: a case-referent study (CHAPS-UK). Hum Reprod. 2012;27(9):2799–806. https://doi.org/10.1093/humrep/des183
4. Zleczewski M, et al. Garment fit, scrotal thermoregulation, and male fertility outcomes: a narrative review. Transl Androl Urol. 2026;15(5):184. https://doi.org/10.21037/tau-2026-1-0139
5. Jung A, et al. Influence of moderate cycling on scrotal temperature. Int J Androl. 2008;31(4):403–7. https://doi.org/10.1111/j.1365-2605.2007.00783.x
6. Wise LA, et al. Physical activity and semen quality among men attending an infertility clinic. Fertil Steril. 2011;95(3):1025–30. https://doi.org/10.1016/j.fertnstert.2010.11.006
7. Gaskins AJ, et al. Paternal physical and sedentary activities in relation to semen quality and reproductive outcomes among couples from a fertility center. Hum Reprod. 2014;29(11):2575–82. https://doi.org/10.1093/humrep/deu212
8. Nikolopoulos I, et al. Scrotal cooling and its benefits to male fertility: a systematic review. J Obstet Gynaecol. 2013;33(4):338–42. https://doi.org/10.3109/01443615.2012.758088
9. Sheynkin Y, et al. Protection from scrotal hyperthermia in laptop computer users. Fertil Steril. 2011;95(2):647–51. https://doi.org/10.1016/j.fertnstert.2010.10.013
10. Avendaño C, et al. Use of laptop computers connected to internet through Wi-Fi decreases human sperm motility and increases sperm DNA fragmentation. Fertil Steril. 2012;97(1):39–45. https://doi.org/10.1016/j.fertnstert.2011.10.012
11. Garolla A, et al. Seminal and molecular evidence that sauna exposure affects human spermatogenesis. Hum Reprod. 2013;28(4):877–85. https://doi.org/10.1093/humrep/det020
12. Hjollund NH, et al. Diurnal scrotal skin temperature and semen quality. Int J Androl. 2000;23(5):309–18. https://doi.org/10.1046/j.1365-2605.2000.00245.x
13. American Urological Association / American Society for Reproductive Medicine. Male Infertility Guideline (2020, amended 2024). https://www.auanet.org/guidelines-and-quality/guidelines/male-infertility
14. NICE NG257. Advice about factors that can affect fertility, recommendation 1.11.1. https://www.nice.org.uk/guidance/ng257/chapter/Advice-about-factors-that-can-affect-fertility
15. McKinnon CJ, et al. Male personal heat exposures and fecundability: a preconception cohort study. Andrology. 2022;10(8):1511–1521. https://doi.org/10.1111/andr.13242

If you would like help sorting which of this applies to the two of you and which parts you can set down for good, Book a free 15-minute call. It is a conversation about your preparation, not a substitute for the advice of your reproductive endocrinologist or urologist.