Did you notice changes to your menstrual cycle during this summer's heatwaves? If so, you're not alone.
The menstrual cycle is controlled by a constant back and forth of hormones, messaging molecules which travel around in the bloodstream and tell tissues and organs what to do. If anything in the environment affects the body’s production of hormones, the result can be a change in the regularity of your cycle and the symptoms it brings. This might be stress (such as from exams, a new relationship, or a house move), but new research is showing that climate change is also wreaking havoc on our hormones: poor air quality, limited food access and extreme temperatures can all impact the menstrual cycle, and all three factors are becoming more prevalent as the planet warms.
So, how do we know? A 2026 study [1] involving 20,000 women aged 18-50 from China found that exposure to extreme heat was associated with lower levels of oestradiol and progesterone, and increased levels of leutenising hormone. These hormones control the menstrual cycle, meaning that such changes can cause irregular periods, as well as having longer term effects on fertility – but they don’t just travel to the uterus and call it a day. Many cells in the body have receptors for reproductive hormones, including (you probably guessed) the brain, which means that when they fluctuate from the norm, it can affect both our mood and pain tolerance. There’s another layer to it too: the menstrual cycle is already an inflammatory process – and extreme heat adds to that inflammation, heightening the sensation of pain. According to gynaecologists, for the same reasons, heatwaves can amplify many of the factors and symptoms associated with conditions like premenstrual dysphoric disorder and endometriosis. One particularly interesting finding was that the impact of heat on progesterone levels (that’s the hormone that maintains the uterus lining) was reduced when a person was able to spend time in nature. It’s believed that this is not just because trees provide a practical source of shade during heatwaves, but because the perception of ‘greenness’ triggers the body to de-stress at a cellular level.
Alongside temperature change, we are also contending with air pollution. Globally, most air pollution is caused by the combustion of fossil fuels to make energy – something which is estimated to affect the health of 1.6 billion people [2]. Other industries with high emissions (fast fashion, transport and intensive agriculture, for example) are also responsible for an array of pollutants. When we breathe in polluted air, harmful particles less than 2.5mm in diametre (known as PM 2.5) can cross the delicate lining of the lungs and circulate around our body in the bloodstream. In 2025, researchers studied over 2.2 million people aged 18-44 from North and South America who had tracked their periods with the app Clue [3]. They found that those who lived in the worst-polluted areas (with highest levels of PM 2.5) were more likely to experience unusual cycle lengths – meaning very short or very long gaps between each period. The exact reason is unknown, but it’s thought to be because pollutants affect oestradiol production, or interfere with the body’s ability to pick up signals from hormones.
Bloody annoying: why do these changes to women's menstrual cycles actually matter?
On top of the health risks, the impact of climate change on menstruation is a question of climate injustice. In recent years, it’s rightly become well-documented that women are more vulnerable to the impacts of climate change, compared to men [4]. The reasons aren’t just physiological, although the increased risk from dehydration during pregnancy and menstruation does have an effect. It’s also sociological; women tend to have more caregiving duties and experience higher poverty levels. As you can imagine, this makes it much harder to escape from climate-related natural disasters or adapt to extreme weather, such as by installing air conditioning or paying for increasingly expensive food. Changes to the menstrual cycle are another piece of the dilemma. Every year, students around the world already miss multiple weeks of school per year due to periods [5]. If climate change makes periods worse, more painful, or access to water difficult, they are likely to miss even more education, deepening the gender divide in education and income. This is a particular risk in low-income countries, where people are facing some of the greatest climate-induced temperature changes, yet – unfairly – also contributed to some of the lowest historic emissions.
What can we do?
If you’re in the UK, this may be one of the first years you’ve really noticed the shifts in extreme weather caused by climate change (it has been the hottest summer since records began). If you have experienced more pain or difficulty going to school or work during the heatwave because of painful periods, then you have already experienced a type of climate injustice. As a priority, we need to dramatically cut our emissions and reliance on fossil fuels. If you want more ideas about how you can do this and get involved in taking action for the planet, you can check out our 30 Steps Programme and (if you’re under 18) the Power of 10 app. Of course, the other problem at the heart of this issue is the stigma and discrimination around menstruation. One of the ways you can be part of changing this is by having open and honest conversations with your friends, and by sharing information on how climate change is disproportionately impacting women’s health. If your school or workplace doesn’t already offer free period products, you could encourage them to do so – did you know that in the UK, the Government funds free products for state schools? Of course, as the first study recommended, spending time somewhere green can help reduce symptoms – more evidence that spending time in nature is a good idea, if you needed it!
And remember, if the recent heatwaves have got you feeling concerned about any symptoms, go to your GP.
References
[1] Fang, L., Ma, C., Zhao, H., Peng, Y., Wang, G., Cai, G., … & Pan, F. (2026). Associations of chronic and acute ambient heat exposure with sex hormones: A longitudinal study in women receiving assisted reproductive technology. Ecotoxicology and Environmental Safety, 314, 120034. https://www.sciencedirect.com/science/article/pii/S0147651326003635?via%3Dihub
[2] Harvey, F. (2025). Fossil fuel burning poses threat to health of 1.6bn people, data shows. The Guardian. https://www.theguardian.com/environment/2025/sep/24/fossil-fuel-burning-threat-health-16bn-people-data-shows
[3] Priyanka, N. D., Shea, A. A., Vitzthum, V. J., Duarte, F., Hanly, C. G., Timmons, M., … & Nethery, R. C. (2025). The effect of air pollution exposure on menstrual cycle health using self-reported data from a mobile health app: a prospective, observational study. The Lancet Planetary Health, 9(5), e364-e373. https://www.thelancet.com/journals/lanplh/article/PIIS2542-5196(25)00080-4/fulltext
[4] United Nations Women (2026). Extreme heat and the unequal consequences of the climate crisis. https://www.unwomen.org/en/articles/explainer/extreme-heat-and-the-unequal-consequences-of-the-climate-crisis
[5] Quilter, M. (2026). Period poverty: a silent crisis. Unicef Australia. https://www.unicef.org.au/stories/period-poverty?srsltid=AfmBOorSHWthAbTIvlFzRfeNa8lSxtoQdUdsbZmz-zKo_nFbpXe4s4WZ
