Women and heat risk: Expert Q&A with Gabrielle Giersch and Nisha Charkoudian
Published: October 29, 2025
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Women have long been underrepresented in biomedical research, and studies on heat exposure are no exception. This gap has fueled myths and misconceptions about how women biologically respond to heat and debates on whether they face greater risks than men due to physiological differences.
To dig into the science, we spoke with two experts who have reviewed the evidence on women, heat, and health. In this conversation with Gabrielle Giersch and Nisha Charkoudian, they share what the research really tells us about women’s risk of heat illness and argue that young healthy women do not have a physiologically-based increased risk of heat illness compared to young men.
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Q: Are healthy women more vulnerable to heat compared to healthy men during physical activity, for example, an athletic event?
A: No, they are not. There is no evidence to suggest that women are at increased risk of heat illness, or that women are more vulnerable to heat stress, when groups of young, healthy men and women are compared directly using robust statistical analyses.
Q: Some evidence says that women sweat less than men. If that is true, that must mean they are more vulnerable to heat.
A: This is a common misconception. Sometimes, but not always, research has shown that women sweat (on average) less than men. However, it’s important to note that there is a huge amount of variability across people in terms of how much people sweat. You could easily have women who sweat heavily, men who sweat only lightly, and everything in-between.
Even in people who sweat more, this is not necessarily an advantage in terms of heat vulnerability, as not all sweat leads to heat dissipation. For example, if a person is exercising in a warm, dry environment, sweating works to cool the body by evaporation (the evaporating sweat absorbs heat). But, if the sweat can’t evaporate (like if you have heavy clothing on or the environment is very humid), then it’s basically “wasted” water for no reason; it doesn’t cool you down. Remember that sweating is literally releasing water from your body, so if you are at risk of getting dehydrated, being prone to heavy sweating will cause you to lose more water and get more dehydrated than if you don’t sweat much.
Q: Are there differences in how young, healthy men and women should prepare for physical activity in the heat?
A: Not necessarily. For everyone, you should begin any exercise session in the heat as hydrated as possible (one way is to see that you are sufficiently hydrated is by urine that is light yellow or clear). You should try to replace sweating losses during exercise, so if an individual tends to sweat more or less, they should consume fluid relative to the amount of sweat they lose. It’s very easy to determine your individual sweating rate: weigh yourself (preferably without clothing) before exercise, exercise as you normally would (i.e, running or cycling) for 30 minutes without fluid (or know the amount of fluid you ingest, like a 20oz bottle), weigh yourself again after, and complete the equation below. Then, during future exercise, try to match the amount of fluid you’ll lose.
Sweat loss = (pre-exercise nude mass – post-exercise nude mass) + fluid consumed or urine produced
Sweating rate = Sweat loss / time
For example: If Sarah weighs 75kg before exercise, 74.75kg after exercise and she consumed 500mL (1mL=1g) of fluid during her 30 min exercise, her sweat loss would be .75L or 1.5L per hour.
There’s no evidence to suggest that these recommendations should be different between men and women.
Q: Women are generally smaller than men, so doesn’t this make them more vulnerable to the negative effects of a hot environment?
A: No. It is true that the physical size of the human body matters when we are trying to cool off in a hot environment. Larger people have larger body surface area (BSA: the area of the whole surface of the body) and larger body mass (they are heavier), but smaller people have a higher ratio of these two, called the BSA/mass ratio. Women tend to be smaller than men (on average) – and since we create body heat based on our body mass (for example, muscles working during exercise) and we dissipate heat based on our body surface area, having a higher ratio of BSA/mass means that women can dissipate heat more effectively in many scenarios. This is also why children or smaller humans are at increased risk of hypothermia when exposed to very cold environments.
The specifics matter, such as clothing and humidity, so it isn’t the case that women are always at an advantage, but it definitely isn’t the case that they are consistently more vulnerable either.
Q: If some people think women are more vulnerable, what harm could it do to just be more careful about women’s activities in the heat?
A: Quite a bit of harm, actually. Historically, women have often been assumed to be more “fragile” than men in various occupational and athletic settings. This was usually presented as “taking care of” women, but in practice often created limits to women’s advancement – even when they were perfectly capable of doing the required tasks.
An example is that women were not “officially” allowed to run the Boston Marathon until 1972, but they have successfully been running marathons and breaking records ever since. Examples of career limitations can be seen in the military and other areas, where women were barred from certain job descriptions or tasks. This was true of the U.S. Military until 2015, when combat roles were opened to women. One of the implications of the previous restrictions was that there were tasks or activities that contributed to promotion that were not open to women – so their career advancement was affected by the restrictions, even if they were physically able to perform the tasks.
Thus, restricting activities based on being more “careful” can limit the trajectory of female performance and careers, without a physiological reason to do so.
Q: What about older men and women and heat stress?
A: This is an important question. Aging decreases the ability of the body to thermoregulate appropriately in the heat – the blood flow and sweating responses of older individuals (both men and women) are decreased compared to younger people, and the heat causes more cardiovascular strain in older people. There is some evidence that older women (post-menopausal) may experience greater thermal strain compared to older men, but this is a population that is even more underrepresented in research, and more research is required to fully understand these potential differences. In general, however, older people (both men and women) need to take extra caution during heat waves, make sure to minimize time in the heat and stay in cool places, with air conditioning if possible.
Q: What about chronic diseases like high blood pressure or diabetes?
A: There’s a lot we still don’t know about the effects of these conditions on heat illness risk, but in general having hypertension (chronic high blood pressure) or diabetes means that your body is less able to defend itself against the heat. These diseases are also associated with altered cardiovascular function – and since heat exposure puts an extra strain on your heart, it is important for people with these conditions to be extra careful when exposed to heat. In this context, though, it is unknown whether men or women are differentially affected in terms of their responses to heat. As with aging, it’s good to just take extra care in hot environments if you have a chronic condition like diabetes or hypertension.
Q: What about non-biological influences on women’s heat illness risk?
A: This is an important question. There is emerging evidence that, across the globe, there are socio-cultural factors that have a strong negative impact on women’s ability to work, train or even survive in extreme heat, which is likely the contributing factor to perceived differences in vulnerability. Fortunately, these issues are gaining more visibility, but it is becoming increasingly clear that there are widespread systemic inequities, including limited access to resources, restrictive gender norms (possibly related to assumptions noted above) and power imbalances for women in many cultures and locations. These can have severe negative consequences for women in terms of resources available to combat the dangers associated with extreme heat. We therefore agree with the idea that reframing any perception of “vulnerability” on the part of women as an equity issue will help to shift the focus of communities towards the promotion of more inclusive and responsive infrastructure and healthcare systems for women.
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About the Experts
Gabrielle Giersch
Gabrielle Giersch, PhD is a research physiologist at the United States Army Research Institute of Environmental Medicine in Natick, MA. Her research focuses on thermoregulatory mechanisms, responses and adaptations to environmental heat stress in men and women, as well as the integrative physiology of responses to environmental extremes of cold and high altitude.
Nisha Charkoudian
Dr. Nisha Charkoudian is a research physiologist and the Chief of the Thermal & Mountain Medicine Division at the U.S. Army Research Institute of Environmental Medicine. Nisha was previously an Associate Professor in the Deptartment of Physiology and Biomedical Engineering at the Mayo Clinic College of Medicine. Her research focuses on mechanisms of control of body temperature and blood pressure in men and women. She is interested in autonomic control mechanisms in responses and adaptations to environmental extremes.
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