Why heatwaves hit women harder: the biology behind the risk

As heatwaves grow longer and more frequent, a growing body of research is pointing to an uncomfortable pattern: women are disproportionately harmed by extreme heat, and the reasons go well beyond simple biology. Health experts are now calling for public awareness campaigns and medical guidance that reflect those differences, rather than treating heat risk as a uniform hazard.

Some of the disparity begins in the body itself. Women generally have a lower sweat rate than men and a higher ratio of surface area to body mass, both of which can make it harder to dissipate heat efficiently. Hormonal fluctuations across the menstrual cycle also affect the body's core temperature and its ability to regulate it, meaning a woman's tolerance for heat can vary meaningfully from week to week, not just from person to person.

Pregnancy adds another layer of risk. Expectant mothers already carry a higher core body temperature and cardiovascular load, and extreme heat has been linked to higher rates of pregnancy complications, including preterm birth. Health researchers say this makes pregnant women one of the groups most in need of tailored heat guidance, yet they are rarely singled out in public messaging that defaults to generic advice about staying hydrated.

Menopause introduces further complexity. Declining oestrogen levels are already associated with impaired temperature regulation and more frequent hot flushes, and researchers say this can compound the physiological strain that extreme ambient heat places on the body, particularly in older women who may also be managing other health conditions.

But experts are equally emphatic that social and economic factors play just as large a role as biology. Women are still more likely than men to carry the bulk of caregiving responsibilities, for children, disabled family members or elderly parents, which can mean spending more time indoors in homes without air conditioning, or being unable to leave for a cooler location because someone depends on them being present.

Occupational patterns matter too. Women make up a large share of the workforce in caregiving professions, such as nursing and social care, which frequently require indoor physical labour in poorly ventilated buildings, alongside outdoor informal and agricultural work in many parts of the world. Both settings can expose workers to sustained heat without straightforward ways to cool down during a shift.

Public health officials say the combination of physiological vulnerability and social exposure has been underappreciated in heat-response planning, which has historically treated the population as a single group with a shared risk profile. That, researchers argue, means women's heat-related health problems can go unrecognised or be misattributed to other causes, delaying treatment during the periods when it matters most.

Addressing the gap, according to health experts, does not require an entirely new framework, but rather adjustments to existing guidance: heat warnings that explicitly mention pregnancy and menopause as risk factors, workplace heat protections that account for indoor caregiving roles, and public cooling spaces designed with women who may be accompanied by young children or elderly relatives in mind.

Some of this work is already under way in trial programmes that track hospital admissions during heatwaves by sex and life stage, aiming to build a clearer evidence base for future public health messaging. Early findings, researchers say, reinforce that a one-size-fits-all approach to heat advice leaves real gaps in protection.

As heatwaves become a fixture of most summers rather than rare emergencies, health experts say closing that gap is no longer optional. Recognising that heat risk is not evenly distributed, they argue, is the first step toward guidance and infrastructure that actually reflect who is most exposed, and why.