Short answer
Heated car seats do warm your scrotum a little. In the only controlled experiment we could find, 90 minutes on a heated seat left the scrotum about half a degree warmer than the same time on an unheated one. But we couldn't find any study that measured sperm in men who use seat heaters, and a large study of couples found little link with how long it took to conceive. Not a crisis. Still, if you're trying for a baby, switching it off costs nothing.
Bit of a niche worry, this, but a fair one on a frosty February commute. Here's what the research measured, and what it didn't.
How much do heated seats warm your testicles?
Jung et al., 2008: 30 men, heated vs unheated seat
What the research found: Thirty healthy men with no history of infertility sat for 90 minutes on a heated car seat and, on a separate occasion, 90 minutes on an unheated one, in random order and in standardised clothing. By the end, scrotal temperature was 0.5°C higher on the left and 0.6°C higher on the right with the heater on. The heated seat overtook the highest temperatures reached on the unheated seat after about a third of the session (Jung et al., 2008).
What it doesn't prove: It measured temperature, not sperm. The authors suggested frequent use adds to the heat stress that comes from sitting for long periods, but the study can't tell you whether half a degree during your drive changes your sperm count.
Does driving itself heat things up?
Bujan et al., 2000: nine men, two hours at the wheel
What the research found: Nine volunteers walked for 40 minutes, then drove for 160 minutes. After two hours of driving, scrotal temperature was 1.7 to 2.2°C higher than while walking (Bujan et al., 2000).
What it doesn't prove: Again, no sperm were counted, and nine men is a very small group. It shows that a couple of hours in a driving position warms things up.
Posture seems to do a lot of the work. In laptop studies, sitting with thighs close together was the main cause of scrotal warming, and sitting with legs apart reduced it (Sheynkin et al., 2011). Our laptop and sperm guide has the full story.
Do heated seats lower sperm count or fertility?
McKinnon et al., 2022: 3,041 couples trying to conceive
What the research found: Men in a large North American study reported their heat habits, including seat heaters, saunas, hot baths and tight underwear, and couples were followed while trying to conceive. Seat heater use showed little association with the chance of conceiving each cycle. Hot tubs, baths and recent fever showed weak links. Men reporting four or more heat exposures had an estimated 23% lower chance of conceiving per cycle than men with none, more so in men aged 30 and over (McKinnon et al., 2022).
What it doesn't prove: Heat habits were self-reported once, and the estimates for multiple exposures were uncertain, with confidence intervals that included no effect. It's reassuring about seat heaters on their own. It hints that heat may add up.
How much heat is enough to affect sperm?
The clearest effects come from bigger doses. Ten men who had two 15-minute saunas a week for three months saw sperm count and motility fall sharply, then fully recover within six months of stopping (Garolla et al., 2013). In another study, twenty men had ten 30-minute sessions of testicular warming in a 43°C water bath, and sperm concentration and motility dropped before recovering (Rao et al., 2015). A heated seat is a much gentler, shorter bump. NICE says raised scrotal temperature is linked with reduced semen quality, while it's uncertain whether measures like looser underwear improve fertility (NICE, 2026).
Should you switch off your heated seat?
If you're trying to conceive, or waiting on a semen test, it's an easy, free change. If you're not, there's no evidence you need to shiver. Either way:
- Use the seat heater to warm up, then turn it off once the cabin is warm.
- Take breaks on long drives. The Highway Code already recommends at least 15 minutes after every two hours of driving (Rule 91), which also gets you out of that warm seated position.
- Wear loose trousers and underwear with room in them for long drives.
- Tackle the bigger heat sources first: saunas, hot tubs, long hot baths and a laptop on your lap.
- Drive for a living? NICE advises clinicians to ask about occupation, so mention it if you see your GP about fertility.
For the full list of everyday heat sources, read our guide to protecting sperm from heat, or take the free five-question Heat Check, an educational habits quiz rather than a fertility test. Every source we use is in our research hub.
Full disclosure: we make a merino boxer with a reusable cooling insert for hot days and long drives. We sell it as comfort. It hasn't been tested against heated seats and hasn't been shown to improve sperm or fertility. If you're curious, you can reserve a founder kit.
Frequently asked questions
Do heated seats cause infertility?
There's no evidence they do. They raise scrotal temperature slightly, and the one large couples study found little association with conception.
How hot does a heated seat make your testicles?
In one experiment, about 0.5 to 0.6°C warmer than an unheated seat after 90 minutes.
Are long drives bad for sperm?
Two hours of driving raised scrotal temperature by around 2°C compared with walking in a small study, but sperm weren't measured. Regular breaks are wise anyway.
Should I stop using heated seats before a semen test or IVF?
It's a sensible, free precaution while you're trying. Tell your clinic about any fever or illness too.
References
- Jung A et al. Influence of heating car seats on scrotal temperature. Fertil Steril, 2008. PMID 17919605
- Bujan L et al. Increase in scrotal temperature in car drivers. Hum Reprod, 2000. PMID 10831568
- Sheynkin Y et al. Protection from scrotal hyperthermia in laptop computer users. Fertil Steril, 2011. PMID 21055743
- McKinnon CJ et al. Male personal heat exposures and fecundability: a preconception cohort study. Andrology, 2022. PMID 35924639
- Garolla A et al. Seminal and molecular evidence that sauna exposure affects human spermatogenesis. Hum Reprod, 2013. PMID 23411620
- Rao M et al. Effect of transient scrotal hyperthermia on sperm parameters, seminal plasma biochemical markers, and oxidative stress in men. Asian J Androl, 2015. PMID 25652627
- NICE. Fertility problems: assessment and treatment (NG257), 2026. nice.org.uk
- Department for Transport. The Highway Code, Rule 91. gov.uk
Last reviewed 24 September 2026.
