Why heatwaves hit women harder than men

Overwhelmed, irritable, dizzy, bloated, exhausted.

These are the words coming up frequently in comments sent to the BBC by women who, having barely recovered from the record-breaking heat in June, are bracing for more hot weather.

Extreme heat can affect anyone. But heatwaves are a "stress-test" for women's cardiovascular systems, and hit them harder than men, said Dr Nighat Arif, an NHS GP who specialises in women's health, told the BBC.

Women may also be marginally more vulnerable to heatwave-related death than men, though more evidence is needed, said Dr Cat Pinho-Gomes, an academic public health consultant at UCL's Institute for Global Health.

So as climate change drives increasingly intense and frequent heatwaves to the UK, experts are calling for better awareness of the risks to women and more targeted efforts to protect them.

Biologically, it comes down to two things: the natural rise and fall of women's hormone levels and our body's response to heat, which are different to men's, Dr Arif said.

Women produce less sweat and start sweating at a higher temperature, research – including this 2025 study, external – shows.

This impairs our ability to quickly shed excess heat and makes it harder to judge when our bodies are under burden, simply because we can't see as much sweat on our skin or clothing.

The same research found, external that women also have a higher core body temperature and body fat percentage than men, which acts like an extra insulating layer.

Now combine this with the natural fluctuations of women's hormones, which already put our brain's temperature regulation systems "out of kilter", according to Dr Arif.

Our levels of oestrogen and progesterone shift most substantially during the menstrual cycle, perimenopause, menopause, pregnancy and while breastfeeding – which can make you less able to regulate your temperature.

All of this is hard work for our cardiovascular systems, especially in hot weather.

But it's not just biology that puts us more at risk, said Dr Pinho-Gomes, co-author of a review into sex differences in heatwave-associated deaths, external.

Our socioeconomic circumstances – such as being lower paid or the most likely caregiver to loved ones – can have an even greater impact on how well we are able to look after ourselves in hot weather, she said.

Age is another factor. The older you are, the more vulnerable you are to heat – and since women live longer on average than men, we are more at risk of health impacts, Dr Pinho-Gomes explained.

Elderly people are also more susceptible to dementia, which can limit the ability to recognise thirst, external, or conditions that require diuretics, used to lower blood pressure – both of which can further expose you to heat-stress, she said.

As hormone levels dip and rise throughout your menstrual cycle, so does your sensitivity to heat, Dr Arif explained.

Progesterone rises during the second half of your cycle, before your period begins. This can raise core body temperature, only adding to the discomfort when you're already hot, she said.

Then the period hits and oestrogen – the hormone which drives your thermoregulatory system – drops to its lowest level, putting more pressure on your heart to cool down.

"I bled a normal amount but noticed a big increase in fatigue, dizziness, anxiety and sleepless nights," said Michaela Finn, from north London, who was on her period during the late June heatwave.

"My shifts at work landed on the same days, too. During my morning shower, I felt faint; I had to be realistic and call in sick. My body was completely exhausted, aching and cramping."

Charlie Paddock, 27, from south London, also said she "nearly fainted twice and the hot flushes were unreal", while Jess Allingham, 26, said she was "absolutely exhausted, more than normal", and had "total brain fog".

When you lose blood through menstruation, you also lose iron, which can affect your sleep, Dr Arif highlighted.

Low iron – which studies show, external is especially common for women with heavy periods – also affects oxygen delivery, giving our cardiovascular systems even more work, she said.

Hot flushes and night sweats are common for perimenopausal and menopausal women due to lowering oestrogen, according to Dr Arif.

The same can happen for women put in a chemical or surgical menopause, which is used to treat hormone-sensitive cancers and major gynaecological conditions, such as endometriosis and polyendocrine metabolic ovarian syndrome (PMOS).

During a heatwave, you may have more frequent and severe hot flushes and night sweats, Dr Arif said - which, according to a study, external on the impact of climate change on menopause, could be further exacerbated by global warming.

"Truly horrendous, especially at night time," is how Hilary Serif, 57, from Cheshire, characterised her hot flushes during the June heatwave.

"You're dozing off and then it hits you from nowhere. You're already warm, there's no relief at all. It's like a double whammy. The good old HRT helps a lot but doesn't control it."

Dr Rosaline West, 41, from Kettering, who is perimenopausal, said enduring the heatwave "was just about survival".

"I was regularly changing my underwear, and by the end... my friend and I had just given up on bras altogether because of that sweatiness, that discomfort."

Pregnant women have a harder time regulating body temperature due to increased metabolic heat and fluid needs, which can make you more prone to heat stress, according to research published in the Lancet, external earlier this year.

Cue the hormones.

Fluctuating progesterone levels during early to mid-pregnancy can make you hotter, the same study shows. It then rises, along with oestrogen, during the latter stages, bringing your body temperature back down.

Your size also makes a difference. "Obviously, there is more cardiovascular burden on the body the bigger you are, because you're carrying a human inside you," Dr Arif explained.

The research also suggests that heat stress may increase the likelihood of adverse outcomes for the mother and child, particularly in higher-risk pregnancies.

Heat exposure has been linked to a higher risk of cardiovascular morbidity and mortality, especially among women, a major review, external of studies on the effects of heat exposure found.

During heatwaves, the added strain on our hearts can cause our blood pressure to lower, which combined with the loss of fluids and salt from sweating, can lead to heat exhaustion.

If blood pressure drops too low, the risk of heart attacks also rises.

Dr Arif advised: "Know the signs of heat exhaustion and heat stroke... drink plenty of fluids, have your fans, your cooling stuff. Make sure you do your exercise before sunrise or after sunset. Use sun cream, track your periods.

"Treat the heat like a cardiovascular stress-test," she said. Slow down, take care of your body.

She also urged employers, colleagues and policymakers to be "more mindful" of women's sensitivity to hot weather.

Dr Pinho-Gomes agreed, adding: "We need more women sitting at the decision table... in positions of power and influence", who will be more aware of women's needs than men.

"This is not a woman's problem," Dr Arif said. "This is a societal problem. If we get it right for women, we get it right for everyone."

With additional reporting from Alix Hattenstone and Mary Litchfield.