In many countries, but particularly in Europe, more women than men die during heat waves. Some researchers have attempted to explain this discrepancy, which is due not only to the fact that women live longer but also to physiological and behavioral factors. During the 2003 heat wave in France, the number of heat-related deaths among people over the age of 55 was 15% higher among women than men of the same age, according to a study published by several researchers at the French National Institute for Health and Medical Research (Inserm) in 2006.

France is far from being an exception. A number of studies have been carried out in the Netherlands, for example, showing significant gender differences in heat wave deaths. In one of the most comprehensive studies on the subject, published in 2021, researchers from the Vrije Universiteit Amsterdam have identified several possible causes. Among them are differences in sweating, cardiovascular tension, the ratio of body surface area to mass, and the greater propensity of women to live alone or to be active in the home. As women live longer (up to 81 in Europe, compared with 75 for men), and are therefore over-represented among the elderly vulnerable to heat, the researchers adjusted their results so as not to overestimate female mortality.

The first explanation put forward by the researchers is that women sweat less and therefore lose less heat. "Sweating is a particularly effective method of cooling, and in this sense, women, who have a lower capacity to perspire and evaporate sweat, are at a disadvantage," noted Hein Daanen, a physiology researcher at the Free University of Amsterdam and co-author of the 2021 study. "When the air temperature exceeds the body temperature [on average between 36°C and 37°C], the only way for the body to lose heat is by sweating," explained Mike Tipton, a researcher at the University of Portsmouth and author of several studies on the subject.

But that's not all – as they regulate their body temperature more by increasing blood transfers to the skin, women are also more likely to develop cardiovascular problems in hot weather. "When it's very hot, there's a sort of detour effect, as blood, which flows more to the skin, can't go as far to other parts of the body, such as, for example, the heart. As the heart receives less blood, it compensates by beating faster, which raises cardiovascular pressure – already higher in women than in men – and increases the associated risks, such as stroke," Daanen said.

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