The Science of Temperature: Understanding Cold and Heat Exposure for Women
Cold exposure advice was built on male physiology. Dr. Stacy Sims defines the temperature thresholds — and the preference for heat — that produce genuine adaptation in women.
Video·Huberman Lab Clips·10 min read·June 2026
Most cold exposure advice was built on male physiology. Dr. Stacy Sims explains the temperature thresholds, sauna benefits, and special cases that actually apply to women.
Deliberate cold exposure has become one of the most discussed recovery tools in performance and wellness circles. For many, the association runs deep — cold showers before dawn, plunges into near-freezing water, the ritual of discomfort as a path to resilience and clarity. But as that conversation has grown louder, a question has emerged with equal force: does the same advice apply to women? The short answer is no. The more important answer begins with understanding why — and that understanding starts with temperature.
I prefer heat for women. Everyone's a responder to the heat.
When a woman enters extremely cold water — temperatures at or below 50°F (10°C) — the body responds with severe vasoconstriction and a cascade of sympathetic nervous system activity. That cascade floods the system with stress signals designed for survival, not adaptation. Circulation constricts sharply, the heart races, and the physiological window for productive recovery closes before it truly opens. This is not a failure of tolerance. It is the body doing precisely what it was built to do — and in this case, that precision works against the clarity and resilience cold exposure is meant to build.
The experience is often described as a gasp, a full-body recoil, the sensation of survival instinct overriding intention. For recovery purposes, that response is counterproductive — the nervous system is not calibrated for adaptation in that state, and the environment of acute stress is one the body is trying to escape, not integrate. The discomfort that marks productive cold exposure and the discomfort that signals a physiological alarm are not the same thing. For women especially, the distinction lies in temperature.
The threshold that changes everything sits at 16°C — roughly 55 to 56°F, the temperature of a cold ocean bay in the early morning. At that level, the water is genuinely challenging. The body releases dopamine, sharpening alertness and lifting mood in the hours that follow. The cardiovascular system activates in ways that drive meaningful adaptation, and the cellular changes that make cold exposure worthwhile begin to take hold. Critically, 16°C does not trigger the extreme vasoconstriction that drives the body into a survival state — it is cold enough to build resilience, and cool enough to remain in the range where adaptation is actually possible.
For women training in open water — triathletes, marathon swimmers, anyone whose race begins with full immersion in conditions that cannot be controlled — preparation requires an additional layer of deliberateness. The face carries a dense concentration of cold receptors; when it meets cold water suddenly, the cardiovascular system responds with a reflex that can spike heart rate and constrict breathing in the opening seconds of competition. Targeted face-first exposure in training habituates the sympathetic nervous system to that initial surge. The goal is not to eliminate the reflex, but to modulate it — so that when the race begins, the body adapts with precision rather than retreating into alarm.
Underlying all of these nuances is a principle that holds across contexts: for women as a general population, heat is the more universally effective modality. Cold exposure has its place, and at the right temperature and with the right protocol, it can produce genuine benefit. But the blanket prescriptions built on male physiology — the near-freezing plunges, the extreme cold benchmarks — require meaningful adjustment before they translate to a different physiology. The thresholds differ; the responses differ; and the practice should honour that difference.
cold yeah for reasons I still don't cold yeah for reasons I still don't understand people have Associated me or understand people have Associated me or understand people have Associated me or this podcast with deliberate cold this podcast with deliberate cold this podcast with deliberate cold exposure I like deliberate cold exposure exposure I like deliberate cold exposure exposure I like deliberate cold exposure in the form of a cold shower or a cold in the form of a cold shower or a cold in the form of a cold shower or a cold plunge or an ice bath mostly for the plunge or an ice bath mostly for the plunge or an ice bath mostly for the effects that occur afterward oh yeah effects that occur afterward oh yeah effects that occur afterward oh yeah yeah and every time I do a post about yeah and every time I do a post about yeah and every time I do a post about deliberate cold exposure I get asked deliberate cold exposure I get asked deliberate cold exposure I get asked understandably so how does it affect understandably so how does it affect understandably so how does it affect women differently than men I prefer heat women differently than men I prefer heat women differently than men I prefer heat for women everyone's a responder to the for women everyone's a responder to the for women everyone's a responder to the heat you get better adaptations sauna heat you get better adaptations sauna heat you get better adaptations sauna yep sauna hot tub yep preferably a true yep sauna hot tub yep preferably a true yep sauna hot tub yep preferably a true finish sauna infrared doesn't it warms finish sauna infrared doesn't it warms finish sauna infrared doesn't it warms the skin but not the core we want thank the skin but not the core we want thank the skin but not the core we want thank you for saying that I'm not a big fan of you for saying that I'm not a big fan of you for saying that I'm not a big fan of infrared sauna because it doesn't get infrared sauna because it doesn't get infrared sauna because it doesn't get hot enough no yeah you can bring an hot enough no yeah you can bring an hot enough no yeah you can bring an infrared light into a traditional sauna infrared light into a traditional sauna infrared light into a traditional sauna if it can tolerate the heat yeah so the if it can tolerate the heat yeah so the if it can tolerate the heat yeah so the thing with cold water exposure is the thing with cold water exposure is the thing with cold water exposure is the whole conversation about ice cold ice whole conversation about ice cold ice whole conversation about ice cold ice baths and how cold it is it's too cold baths and how cold it is it's too cold baths and how cold it is it's too cold for women
for women for women because when we're looking at that because when we're looking at that because when we're looking at that severe immediate jump into that icy cold severe immediate jump into that icy cold severe immediate jump into that icy cold it causes such severe constriction and it causes such severe constriction and it causes such severe constriction and shut down so women do really well and shut down so women do really well and shut down so women do really well and get that whole dopamine response and get that whole dopamine response and get that whole dopamine response and everything if the water is around 16° C everything if the water is around 16° C everything if the water is around 16° C which is 55 to 56 Dees Fahrenheit which which is 55 to 56 Dees Fahrenheit which which is 55 to 56 Dees Fahrenheit which is chilly it's chil it's not warm no is chilly it's chil it's not warm no is chilly it's chil it's not warm no it's go dive in San Francisco Bay right it's go dive in San Francisco Bay right it's go dive in San Francisco Bay right and that is enough enough to offset that and that is enough enough to offset that and that is enough enough to offset that severe constriction survival but it is severe constriction survival but it is severe constriction survival but it is cold enough to invoke all the changes cold enough to invoke all the changes cold enough to invoke all the changes that we want with cold water that we want with cold water that we want with cold water exposure so it's a temperature Nuance exposure so it's a temperature Nuance exposure so it's a temperature Nuance that's that sex difference and like I that's that sex difference and like I that's that sex difference and like I said when I have Open Water swimmers who said when I have Open Water swimmers who said when I have Open Water swimmers who are going to do a long swim or they're are going to do a long swim or they're are going to do a long swim or they're going to do a triathlon and the water is going to do a triathlon and the water is going to do a triathlon and the water is colder I have them do cold water colder I have them do cold water colder I have them do cold water exposure especially face exposure into exposure especially face exposure into exposure especially face exposure into the cold water um to get them habituated
the cold water um to get them habituated the cold water um to get them habituated to that initial severe constriction and to that initial severe constriction and to that initial severe constriction and sympathetic activity that we don't want sympathetic activity that we don't want sympathetic activity that we don't want to happen before a to happen before a to happen before a rice with heat being the true like true rice with heat being the true like true rice with heat being the true like true heat that we're talking about with sauna heat that we're talking about with sauna heat that we're talking about with sauna we see a lot of metabolic changes for we see a lot of metabolic changes for we see a lot of metabolic changes for women so we're having better insulin and women so we're having better insulin and women so we're having better insulin and glucose control we're seeing uh a better glucose control we're seeing uh a better glucose control we're seeing uh a better um expression of our heat shock proteins um expression of our heat shock proteins um expression of our heat shock proteins and the uncoupling and and the and the uncoupling and and the and the uncoupling and and the rebuilding of those proteins better are rebuilding of those proteins better are rebuilding of those proteins better are cardiovascular responses and then for cardiovascular responses and then for cardiovascular responses and then for women as we get older and have the women as we get older and have the women as we get older and have the offshoot of hot flashes night sweats offshoot of hot flashes night sweats offshoot of hot flashes night sweats that kind of stuff if you're doing heat that kind of stuff if you're doing heat that kind of stuff if you're doing heat exposure you're sending a stronger exposure you're sending a stronger exposure you're sending a stronger stimulus to the stimulus to the stimulus to the hypothalamus and you're also getting a hypothalamus and you're also getting a hypothalamus and you're also getting a better serotonin production from the gut better serotonin production from the gut better serotonin production from the gut because we have 95% of our serotonin because we have 95% of our serotonin because we have 95% of our serotonin produced from the gut
produced from the gut produced from the gut which lends to better temperature which lends to better temperature which lends to better temperature control and shuts down hot flashes so control and shuts down hot flashes so control and shuts down hot flashes so it's not that you disapprove of the of it's not that you disapprove of the of it's not that you disapprove of the of using deliberate cold exposure you just using deliberate cold exposure you just using deliberate cold exposure you just recommend that women do deliberate cold recommend that women do deliberate cold recommend that women do deliberate cold exposure with temperatures that are exposure with temperatures that are exposure with temperatures that are maybe in the um low 50 degree Fahrenheit maybe in the um low 50 degree Fahrenheit maybe in the um low 50 degree Fahrenheit um Range as opposed to the really H um Range as opposed to the really H um Range as opposed to the really H frankly just painfully cold for anybody frankly just painfully cold for anybody frankly just painfully cold for anybody um you know 38 to you know 50 degree um you know 38 to you know 50 degree um you know 38 to you know 50 degree temperatures I've been asked whether or temperatures I've been asked whether or temperatures I've been asked whether or not pregnant women can do deliberate not pregnant women can do deliberate not pregnant women can do deliberate cold exposure probably no fewer cold exposure probably no fewer cold exposure probably no fewer than 2500 times on social media and I than 2500 times on social media and I than 2500 times on social media and I never have an answer and but I always never have an answer and but I always never have an answer and but I always default to the cautious answer which is default to the cautious answer which is default to the cautious answer which is uh please don't until you talk to uh please don't until you talk to uh please don't until you talk to somebody who actually has an answer yeah somebody who actually has an answer yeah somebody who actually has an answer yeah just because it sounds like a very just because it sounds like a very just because it sounds like a very precarious situation but in all honesty precarious situation but in all honesty precarious situation but in all honesty I don't know I'm just biting time there I don't know I'm just biting time there I don't know I'm just biting time there and just saying please go ask somebody and just saying please go ask somebody and just saying please go ask somebody who can give you a definitive answer yes who can give you a definitive answer yes who can give you a definitive answer yes so we see women who have a high risk for
so we see women who have a high risk for so we see women who have a high risk for miscarriage that anything that they do miscarriage that anything that they do miscarriage that anything that they do that's incredibly stressful for the that's incredibly stressful for the that's incredibly stressful for the first 12 to 20 first 12 to 20 first 12 to 20 weeks will put them at a higher risk for weeks will put them at a higher risk for weeks will put them at a higher risk for it so being very cautious especially it so being very cautious especially it so being very cautious especially with cold because we know that there are with cold because we know that there are with cold because we know that there are so many different nuances doing so many different nuances doing so many different nuances doing something like hot yoga when you're something like hot yoga when you're something like hot yoga when you're pregnant is not there is research so pregnant is not there is research so pregnant is not there is research so it's not it's not it's not detrimental yeah because when we're detrimental yeah because when we're detrimental yeah because when we're looking at blood flow diversion that way looking at blood flow diversion that way looking at blood flow diversion that way when you have slight when you have slight when you have slight hypoxia to the placenta and to the baby hypoxia to the placenta and to the baby hypoxia to the placenta and to the baby there is a rebound effect that increases there is a rebound effect that increases there is a rebound effect that increases the the the vascularization so that the baby has vascularization so that the baby has vascularization so that the baby has better nutrients we see this also with better nutrients we see this also with better nutrients we see this also with like exercise and exercise intensities like exercise and exercise intensities like exercise and exercise intensities this is why people are now saying you this is why people are now saying you this is why people are now saying you need to have some kind of blood flow need to have some kind of blood flow need to have some kind of blood flow change and increase in core temperature change and increase in core temperature change and increase in core temperature to create these vascular effects within to create these vascular effects within to create these vascular effects within the placenta to improve nutrient and the placenta to improve nutrient and the placenta to improve nutrient and nutrient delivery to the developing
nutrient delivery to the developing nutrient delivery to the developing fetus so Heat's good cold I'm not so fetus so Heat's good cold I'm not so fetus so Heat's good cold I'm not so sure of but probably not extreme heat sure of but probably not extreme heat sure of but probably not extreme heat not extreme heat so that's what I mean not extreme heat so that's what I mean not extreme heat so that's what I mean like hot yoga is not going to the sauna like hot yoga is not going to the sauna like hot yoga is not going to the sauna Hot Yoga sits around 40 degrees cels so Hot Yoga sits around 40 degrees cels so Hot Yoga sits around 40 degrees cels so what is that just around 100 degrees what is that just around 100 degrees what is that just around 100 degrees Fahrenheit and in that situation if Fahrenheit and in that situation if Fahrenheit and in that situation if you're feeling too hot you leave you lie you're feeling too hot you leave you lie you're feeling too hot you leave you lie down on the floor don't try to stay for down on the floor don't try to stay for down on the floor don't try to stay for the whole class um but it's not going to the whole class um but it's not going to the whole class um but it's not going to be detrimental unless you're pushing be detrimental unless you're pushing be detrimental unless you're pushing yourself too much again everything in yourself too much again everything in yourself too much again everything in moderation especially when you're moderation especially when you're moderation especially when you're pregnant it's almost the inverse of what pregnant it's almost the inverse of what pregnant it's almost the inverse of what we know for males which is if men want we know for males which is if men want we know for males which is if men want to conceive they should avoid the sauna to conceive they should avoid the sauna to conceive they should avoid the sauna because we know that heat is detrimental because we know that heat is detrimental because we know that heat is detrimental to sperm viability in a in a real way so to sperm viability in a in a real way so to sperm viability in a in a real way so much so that I tell guys if they are much so that I tell guys if they are much so that I tell guys if they are trying to get their partner pregnant trying to get their partner pregnant trying to get their partner pregnant that they should bring an ice pack into that they should bring an ice pack into that they should bring an ice pack into the sauna they should insulate that ice the sauna they should insulate that ice the sauna they should insulate that ice pack don't put it directly on the pack don't put it directly on the pack don't put it directly on the scrotum for for other reasons but that scrotum for for other reasons but that scrotum for for other reasons but that it's a you know that the effects of heat
it's a you know that the effects of heat it's a you know that the effects of heat the negative effects of heat on sperm the negative effects of heat on sperm the negative effects of heat on sperm are are real yeah but there's also an are are real yeah but there's also an are are real yeah but there's also an interesting it's not just a trend interesting it's not just a trend interesting it's not just a trend there's actually some research showing there's actually some research showing there's actually some research showing that um cooling the testicles leads to that um cooling the testicles leads to that um cooling the testicles leads to increases in testosterone which is on increases in testosterone which is on increases in testosterone which is on the face of It kind of um the face of It kind of um the face of It kind of um counterintuitive counterintuitive counterintuitive because turns out that it's about the because turns out that it's about the because turns out that it's about the Vaso Vaso Vaso constriction causing the subsequent constriction causing the subsequent constriction causing the subsequent increase in blood flow in inreased vasal increase in blood flow in inreased vasal increase in blood flow in inreased vasal dilation so the inverse of what you just dilation so the inverse of what you just dilation so the inverse of what you just said which is that during the heating said which is that during the heating said which is that during the heating process the hypoxia induces more process the hypoxia induces more process the hypoxia induces more vascularization of the of the placenta vascularization of the of the placenta vascularization of the of the placenta yeah so um when talking about yeah so um when talking about yeah so um when talking about temperature one always has to think temperature one always has to think temperature one always has to think about the surface of the body versus the about the surface of the body versus the about the surface of the body versus the brain response as we talked about brain response as we talked about brain response as we talked about earlier and then what's happening during earlier and then what's happening during earlier and then what's happening during the deliberate heat or deliberate Cold the deliberate heat or deliberate Cold the deliberate heat or deliberate Cold versus what's happening after the versus what's happening after the versus what's happening after the deliberate heat or deliberate cold right deliberate heat or deliberate cold right deliberate heat or deliberate cold right everything in biology is a process not everything in biology is a process not everything in biology is a process not an event yeah and I should make full an event yeah and I should make full an event yeah and I should make full disclosure I started as an environmental disclosure I started as an environmental disclosure I started as an environmental exercise physiologist in my PhD was all
exercise physiologist in my PhD was all exercise physiologist in my PhD was all in heat and heat research so I'm a in heat and heat research so I'm a in heat and heat research so I'm a little bit biased towards heat but I've little bit biased towards heat but I've little bit biased towards heat but I've done a significant amount of research in done a significant amount of research in done a significant amount of research in the hot and cold thank you for the the hot and cold thank you for the the hot and cold thank you for the disclosure I I see it more as a uh as an disclosure I I see it more as a uh as an disclosure I I see it more as a uh as an indication of of real knowledge so thank indication of of real knowledge so thank indication of of real knowledge so thank you this is an aspect of your training I you this is an aspect of your training I you this is an aspect of your training I I knew a little bit about based on your I knew a little bit about based on your I knew a little bit about based on your Publications but I didn't realize the Publications but I didn't realize the Publications but I didn't realize the depth of knowledge so we're all depth of knowledge so we're all depth of knowledge so we're all benefiting here [Music]
Transcript auto-generated by YouTube. Verbatim — duplicates intentionally preserved.
Traditional Finnish sauna is the modality of choice — not infrared, which warms the skin's surface without meaningfully raising core temperature. The distinction is not a matter of preference. Core temperature is what drives the physiological adaptations that make heat exposure genuinely transformative. Infrared can be a pleasant experience, but skin-level warmth and core-level heat are not interchangeable. The goal is to heat the body from within, and a traditional sauna accomplishes this in ways infrared does not reach.
You're sending a stronger stimulus to the hypothalamus and you're also getting a better serotonin production from the gut.
When core temperature rises under genuine sauna conditions, the cardiovascular response is pronounced, the hormonal signals intensify, and the cellular rebuilding that follows is more complete. Skin-level warming produces comfort; core-level heat produces change. For women seeking the full metabolic and neurological benefit that heat has to offer, the modality must reach deep enough to matter. A session that leaves core temperature unchanged has not delivered the stimulus.
Among the most significant benefits of regular sauna use is the improvement in metabolic function. Consistent heat exposure enhances insulin sensitivity and supports more precise glucose control — outcomes that matter across the lifespan, and that carry particular weight as hormonal changes alter metabolic baseline. Heat stress prompts the body to upregulate the systems that manage glucose regulation, delivering a benefit that compounds with consistent practice. For women navigating metabolic shifts at any life stage, this adaptation is one of sauna's most direct contributions to long-term vitality.
Heat shock proteins are among the body's most important cellular repair mechanisms. When core temperature rises under sauna conditions, heat shock protein expression increases, initiating the uncoupling and rebuilding of damaged proteins throughout the body. The result is cellular recovery — not simply as a response to exercise, but as an ongoing process of maintenance and longevity. The sauna, understood this way, is not a form of rest. It is deliberate regeneration.
The cardiovascular adaptations that accumulate from regular heat exposure add another dimension to sauna's value. Repeated sessions train the heart and circulatory system to respond more efficiently to thermal stress, building a cardiovascular resilience that extends well beyond each individual session. The body learns to manage circulation under demand — an adaptation that improves cardiovascular function across a range of contexts. For women, these changes accumulate into meaningful long-term benefit, particularly as cardiovascular health becomes an increasingly central concern with age.
For women navigating perimenopause and menopause, sauna offers a particularly direct and well-supported benefit. Hot flashes and night sweats arise when the hypothalamus — the brain's thermostat — loses its calibration as oestrogen levels shift. Regular heat exposure sends a stronger, more consistent thermal stimulus to the hypothalamus, helping to recalibrate that system over time. The result is a measurable reduction in hot flash frequency — achieved not through suppression, but through sustained physiological retraining. The body is reminded how to regulate itself.
A second mechanism deepens this benefit, and it is less widely understood. Ninety-five percent of the body's serotonin is produced in the gut — and serotonin plays a central role in temperature regulation, not only in mood. Sauna-driven heat exposure improves gut serotonin output, giving the hypothalamus better neurochemical support for maintaining equilibrium. When gut serotonin production is optimised, the system governing core temperature functions with greater precision, and the dysregulated surges that produce hot flashes diminish. Heat, in this respect, works with the body's own chemistry — and the steadiness that comes from stable temperature regulation extends into mood and mental clarity as well.
Pregnancy introduces a different framework — and with cold exposure, the appropriate starting point is caution. In the first 12 to 20 weeks, the physiological systems governing fetal development are particularly sensitive to acute stress. Extreme cold reliably induces a significant stress response, and in pregnancies that carry elevated miscarriage risk, the recommendation is clear: avoid it. The science here is not yet fully settled, and the prudent position is to seek clinical guidance rather than follow a general protocol.
Heat during pregnancy, by contrast, has a more nuanced and better-researched profile. Hot yoga, practiced at approximately 40°C (100°F), has research support behind it. At that temperature, a mild elevation in core temperature and the associated shift in blood flow create slight, transient hypoxia at the placenta. Rather than being harmful, this triggers placental vascularization — the growth of new blood vessels that improve nutrient and oxygen delivery to the developing fetus. The body responds to mild thermal challenge by building more capacity, and the fetus benefits directly from that adaptation.
The principle is calibrated challenge, not the avoidance of all thermal stress. Moderate heat in a managed environment produces adaptation; extreme heat sustained past the body's signals produces risk. A pregnant woman who becomes too warm should stop, rest, and cool — the session is never more important than the signal the body is sending. Mild hypoxia, within a physiologically manageable range, triggers growth; severe hypoxia, sustained, causes harm. Moderation here is not compromise — it is the mechanism itself.
The contrast with male fertility is almost precisely inverse. For men attempting to conceive, sauna use carries a documented risk: heat degrades sperm viability in ways that are both measurable and meaningful. Where moderate heat supports fetal development, sustained heat undermines sperm production at the point of origin. For men in this phase, avoiding prolonged heat exposure is the clear recommendation — and in contexts where sauna is an established part of a recovery protocol, active testicular cooling during sessions has been suggested as a mitigation.
Targeted cooling of the testes carries an additional dimension that is still emerging in research. The vasoconstriction produced by cold exposure, followed by the rebound vasodilation that occurs as the body returns to equilibrium, appears to support an increase in testosterone. The mechanism mirrors what happens with placental vascularization during pregnancy — a temporary reduction in blood flow triggers a compensatory increase, and in this case that increase delivers hormonal benefit. The same biological logic — controlled stress, withdrawal, rebound — appears to operate across different systems and different contexts.
Everything in biology is a process, not an event.
All of this — the heat adaptations, the cold thresholds, the hormonal responses, the cellular repair — points to a single organising insight. Biology is a process, not an event. What happens in the sauna or the cold plunge is the stimulus; what matters is what unfolds in the hours that follow. The body rebuilds, recalibrates, and adapts during the recovery window, not during the session itself. Understanding this reframes the practice: the goal is not to endure the heat or the cold, but to set adaptation in motion and allow the process to complete.
