ahcadvocacy
New member
We get a lot of questions about hot tubs and their safety while TTC. I am not a doctor, but I sure have read a bunch on the topic. We also get questions about saunas, jacuzzis, hot yoga, fevers, hot baths or showers, and I’m going to attempt to get to the nitty gritty so you can make the best decisions for yourself weighing the benefits vs the risks.
Testes function better below human core body temperature - they actually get raised or lowered to maintain a temperature of about 35 °C. (wikipedia) If you submerge them in hot water, they can’t self-regulate.
So, hot tubs are not great for sperm. How bad are they? (Well, taking a dip every 3 months is not a valid form of birth control - right?). In a fairly small study, infertile testes-havers that spent more than 30 minutes in a hot tub per week were asked to abstain and those who did saw great improvement. (Shefi et al 2007). Not hot tubs, but testes-havers who worked in bakeries were found to have 22.7% prevalence of infertility over 3% in the control group. (Al-Otaibi 2018). Anything further is beyond my scope - please enjoy this lovely review paper. Figure 1 is great - hot tubs and professional baking are definitely “toxic exogenous factors”.
If you’ve had a bad semen analysis, please talk to your doctor about laptops, tight pants, cats etc. Way way beyond my scope.
There is lots of evidence that high core body temperature (above 39° C or so) can act as a teratogen (causes an increases in abnormalities with embryos or fetuses). (Edwards 1986, Edwards 2006. Higher core body temperature can be caused by fever, excessive exercise, or you guessed it, hot tubs. Most of the research available focuses on the effects on pregnancy, not on conception, just a heads up if you’re clicking on links.
Organization of Teratology Information Services (OTIS) says keep it below 101º F.
ACOG says below 102.2º F (39° C).
Because homeostasis and physics.
If you hooked a human up directly to 240-volt hot tub heater, and it dumped 6000 watts into them… it would take 2 minutes. And they’d be dead. Not great.
If we rolled you up in a magic perfectly insulating blanket that didn’t allow you lose any heat, assuming you run at about 90 watts? An hour and a half. Maybe two hours, if we cut you an air hole.
The answer is somewhere between those two things. Probably about 30 minutes is a bad idea.
It’s important to note that humans have a fairly high specific heat capacity. It takes a lot of energy to change our temperature. If you’ve ever found yourself too hot or cold via environmental exposure, I’m sure you remember how long and how much effort it took to get back to normal.
Because you feel hot before you get hot. Your skin is designed to protect you from environmental stuff, and you will start to feel sweaty, hot, tired, dizzy, nauseous, and uncomfortable. Most people will want to get out before your core body temperature gets into the danger zone. General safety recommendations are that you should get out after 15-30 minutes, and that you not be under the influence of drugs or alcohol - because falling asleep is the way most people get dangerously overheated.
They’re in the same club at hot tubs - when you’re submerged and can’t thermoregulate in many of your normal ways, you’re at higher risk for overheating. Consider the above risk management techniques where possible.
You’re good. Both of these things are constantly losing heat to the environment, it would be very challenging to raise your core body temperature this way.
Water is a better conductor of heat than air, so it would take longer to affect your core body temperature than a hot tub. I cannot pinpoint the duration of exposure that would be problematic, but it’s the same as hot tubs- if you’re feeling too hot (dizzy, nauseous, tired), go cool down.
Take some acetaminophen, drink water, rest. Treating the fever reduces the risk.
Yeah, don’t exercise until you overheat. It’s not easy to do, though.
Please enjoy.
It’s fine, don’t fall asleep on it.
Cool! Do whatever feels right to you.
(CW: Pregnancy)
So, there was a really interesting review paper (Ravelli et al 2018) on pregnant women and activities that are generally considered higher risk for raising core body temperature. Very good, thorough paper. Their conclusion:
Admittedly, that’s the ACOG level (102.2°F or 39°C), not the OTIS recommendation. OTIS says anything higher than 101 is a concern, it’s very easy to get to 102 and you might not feel uncomfortable - I believe these are very cautious recommendations.
So, this is my opinion based on my best review of the available evidence. I personally agonized over sauna use, and ended up doing a lot of homework because of it. I hope it enables other people to make a more informed risk-benefit analysis when it comes to things that bring us comfort, help us cope, or make us feel good. Remember that while a particular activity may not worth the risk to you, for others the benefits may outweigh the risks.
Edited: Formatting
What’s the big worry with Hot Tubs?
…For people with testes:
Testes function better below human core body temperature - they actually get raised or lowered to maintain a temperature of about 35 °C. (wikipedia) If you submerge them in hot water, they can’t self-regulate.
So, hot tubs are not great for sperm. How bad are they? (Well, taking a dip every 3 months is not a valid form of birth control - right?). In a fairly small study, infertile testes-havers that spent more than 30 minutes in a hot tub per week were asked to abstain and those who did saw great improvement. (Shefi et al 2007). Not hot tubs, but testes-havers who worked in bakeries were found to have 22.7% prevalence of infertility over 3% in the control group. (Al-Otaibi 2018). Anything further is beyond my scope - please enjoy this lovely review paper. Figure 1 is great - hot tubs and professional baking are definitely “toxic exogenous factors”.
If you’ve had a bad semen analysis, please talk to your doctor about laptops, tight pants, cats etc. Way way beyond my scope.
… For uterus havers
There is lots of evidence that high core body temperature (above 39° C or so) can act as a teratogen (causes an increases in abnormalities with embryos or fetuses). (Edwards 1986, Edwards 2006. Higher core body temperature can be caused by fever, excessive exercise, or you guessed it, hot tubs. Most of the research available focuses on the effects on pregnancy, not on conception, just a heads up if you’re clicking on links.
Organization of Teratology Information Services (OTIS) says keep it below 101º F.
ACOG says below 102.2º F (39° C).
Why this is complicated:
Because homeostasis and physics.
- Humans like a narrow range of temperature, and we are constantly working to regulate that in many ways. We sweat, our blood vessels dilate, and we have behavioural responses - drinking cool water, seeking cooler environments.
- Let’s talk physics. You’re a human that weighs 150lbs. You’re roughly cylindrical, and you have the density of a human. You are sitting in a hot tub that is heated to maintain a temperature of 40 °C. Your body temperature averages out to 37 °C. How long can you sit in the hot tub before your core body temperature reaches the same temperature as the hot tub?
- You have a surface area, and your skin temperature is lower than your internal temperature. A hot tub overwhelms most of your methods of losing heat, but some portion of you is still above water, breathing air and losing heat through your head.
- Is the hot tub outside? Is it snowing? Did you go skiing? Did other people get in as well? Did you have a cover on it? How’s the insulation, does it only have a 120-volt heater? There may be many things that are going to be working against it boiling you like a lobster.
If you hooked a human up directly to 240-volt hot tub heater, and it dumped 6000 watts into them… it would take 2 minutes. And they’d be dead. Not great.
If we rolled you up in a magic perfectly insulating blanket that didn’t allow you lose any heat, assuming you run at about 90 watts? An hour and a half. Maybe two hours, if we cut you an air hole.
The answer is somewhere between those two things. Probably about 30 minutes is a bad idea.
It’s important to note that humans have a fairly high specific heat capacity. It takes a lot of energy to change our temperature. If you’ve ever found yourself too hot or cold via environmental exposure, I’m sure you remember how long and how much effort it took to get back to normal.
Why none of this matters so much:
Because you feel hot before you get hot. Your skin is designed to protect you from environmental stuff, and you will start to feel sweaty, hot, tired, dizzy, nauseous, and uncomfortable. Most people will want to get out before your core body temperature gets into the danger zone. General safety recommendations are that you should get out after 15-30 minutes, and that you not be under the influence of drugs or alcohol - because falling asleep is the way most people get dangerously overheated.
So, what could you do to decrease risk?
- Decrease exposure time - 10 minutes or less.
- Decrease temperature - can’t go above 102 if the water is below 102
- Sit with your just your legs in.
- Take regular breaks
- Have a timer or clock to keep track of time
- Have somebody else with you to make sure you don’t fall asleep
- Take a thermometer with you. For science.
What about steam rooms, saunas, jacuzzis?
They’re in the same club at hot tubs - when you’re submerged and can’t thermoregulate in many of your normal ways, you’re at higher risk for overheating. Consider the above risk management techniques where possible.
What about hot baths/showers?
You’re good. Both of these things are constantly losing heat to the environment, it would be very challenging to raise your core body temperature this way.
Hot yoga?
Water is a better conductor of heat than air, so it would take longer to affect your core body temperature than a hot tub. I cannot pinpoint the duration of exposure that would be problematic, but it’s the same as hot tubs- if you’re feeling too hot (dizzy, nauseous, tired), go cool down.
Fever?
Take some acetaminophen, drink water, rest. Treating the fever reduces the risk.
Exercise?
Yeah, don’t exercise until you overheat. It’s not easy to do, though.
Microwaved heat pack for cramps?
Please enjoy.
Electric heating pad for cramps?
It’s fine, don’t fall asleep on it.
This doesn’t feel worth the risk.
Cool! Do whatever feels right to you.
(CW: Pregnancy)
So, there was a really interesting review paper (Ravelli et al 2018) on pregnant women and activities that are generally considered higher risk for raising core body temperature. Very good, thorough paper. Their conclusion:
Admittedly, that’s the ACOG level (102.2°F or 39°C), not the OTIS recommendation. OTIS says anything higher than 101 is a concern, it’s very easy to get to 102 and you might not feel uncomfortable - I believe these are very cautious recommendations.
Let’s all be cool
So, this is my opinion based on my best review of the available evidence. I personally agonized over sauna use, and ended up doing a lot of homework because of it. I hope it enables other people to make a more informed risk-benefit analysis when it comes to things that bring us comfort, help us cope, or make us feel good. Remember that while a particular activity may not worth the risk to you, for others the benefits may outweigh the risks.
Edited: Formatting
I never said it couldn't be done, just that it was harder. I would argue that insemination is easier than finding a third party surrogate. 
I'm a software engineer focused on avionics data processing plus an uncompleted 3 years of a chemistry undergrad before I switched majors to CompSci & Math (got bored with running test tubes through machines). I married a Mechanical Engineer that focuses on modelling HVAC systems. I'll ask him later tonight for his thoughts on this whole equation.