Lower productivity, higher mortality rates, and indoor overcooling. Here’s why heat waves are so much worse for women

Extreme heat is hitting a breaking point. Scorching temperatures are causing major adverse health effects across physical, mental, cognitive, and financial health. And it’s worse for women.

Recent research shows women face a greater proportional loss in income and an increase in caregiving burden as a result of extreme heat. And their overall health is at increased risk too. Women have the “dual health burden” of greater physical susceptibility to heat stress in addition to extra responsibilities associated with heat-related illness in their families.

Just look at mortality rates during heat waves. Extreme heat deaths were higher for women across France, Spain, the Czech Republic, the Netherlands, and India. During the summer of 2022, it is estimated that there were 56% more heat-related deaths in women than in men in Europe. Why is this happening? And why is extreme heat so much worse for women?

Physical susceptibility to temperature

Research is expanding on gender and thermoregulation, and some of it is conflicting. Studies point to different factors that could explain women’s particular vulnerability. Factors include lower sweat output in heat, greater presence of body fat in women, decreased peripheral blood perfusion, and lower thresholds for temperature sensitivity.

Studies on how we adapt physically to heat show women may require greater intensity, frequency, and duration of heat exposure to acclimatize, much like what happened at the Tokyo Olympics. And while the underlying mechanisms are still being studied, it’s clear that we need to be aware of the differences that exist.

Barriers to thermal comfort

Extreme outdoor heat bears important risks, but a distinct battle awaits women indoors. Energy use for indoor cooling has more than tripled since 1990. A known driver has been the excessive cooling of offices, or “overcooling,” which is linked with male-centric indoor climate regulation.

Indoor temperature ranges are based on an average male. Overcooling is more likely to negatively affect women, who report lower thermal satisfaction, especially in the summer heat. This is attributed to gender differences in physiology and clothing selection, and the gender gap in comfort widens when larger groups of people share one thermostat.

Beyond overall well-being, thermal comfort impacts performance for women office workers. A 2019 paper studied the impact of temperature on cognitive performance and found that women do better on math and verbal tasks at higher temperatures. Men saw the reverse effect. A 2021 literature review similarly showed that women have better cognitive performance in a warmer environment with differences of up to 3°C in thermal comfort across genders.

Reproductive health risks and complications

Periods of extreme heat can also have a range of negative effects on reproductive health. When it comes to menstruation, women may notice irregular periods, heavier bleeding, increased pain (known as dysmenorrhea), and even an absence of menstruation in extreme cases.

Women exposed to extreme heat are also more likely to experience fertility problems. While irregular periods can play a role, high temperatures can cause damage to eggs, lower egg reserves, and impair ovulation. Dehydration related to extreme heat can further make it difficult for sperm to reach the egg, negatively impacting conception rates (on top of the decline in sperm production during hot weather).

For those who are pregnant, the CDC cites unique risks. During pregnancy, the body has to work harder to cool down and internal body temperature may rise in very hot environments. Pregnant women are at greater risk of dehydration and are more likely to develop heat-related illnesses, including heat exhaustion and heat stroke. In some cases, there may be links to birth defects and pregnancy complications including preterm labor, premature birth, gestational diabetes, and preeclampsia with negative impacts on both mother and newborn health. In addition, common pregnancy complaints like swollen feet, hands, and ankles can worsen in extreme heat.

Things can feel worse during menopause

It’s no surprise that hot flushes are uncomfortable, but they can be especially grueling during a sudden summer heat wave or prolonged heat dome.

Heat vulnerability is thought to increase after menopause given a lack of estrogen production. Estrogen supports thermoregulation and, when levels decrease around menopause, it can be more challenging to adapt to sudden temperature increases outside a woman’s “thermoneutral zone” (the temperature range in which she neither shivers nor sweats). Hot flushes are also impacted by geography. Hot flush frequency increases with temperature extremes and seasonal temperature changes in continental climates. These extremes are only predicted to increase in the coming years.

Today’s approach to heat stress was designed for a rapidly disappearing Goldilocks Zone – and never properly accounted for critical gender differences. Let’s rethink evolving heat health risks and new solutions to address them, like parametric insurance and other creative tools to safeguard women’s health and finances at the same time.

Now is the time to develop gender-sensitive heat adaptation plans and prepare for the future. If animals can shape-shift to adapt to new extremes, we can recalibrate too.

Talia Varley, M.D., is the physician lead, of advisory services, at Cleveland Clinic Canada where she is a practicing clinician and an ESG insights leader with in-depth work in the “S”.

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