Year after year, heatwaves are getting hotter and more deadly. According to some estimates, heatwaves already kill more people than hurricanes and floods combined. But apparently, what doesn’t kill you makes you… older. According to a new study carried out in Taiwan, every year’s worth of heatwaves could add about two weeks of aging to your body.

Hotter and Hotter

Over the past decade, heatwaves have rewritten the record books with deadly consequences. In 2021, the Pacific Northwest, a region famed for its cool, damp climate, endured a “heat dome” that pushed temperatures above 49 °C (121 °F) in Canada, killing hundreds in just a few days. In 2022, India and Pakistan sweltered through weeks of extreme heat that scorched crops and endangered hundreds of millions of people. And this year, southern Europe’s heatwave sent temperatures soaring past 45 °C in several countries, overwhelming hospitals and prompting widespread warnings from health agencies.

Each of these events would be a rare occurrence in previous times. But with climate change, they become more likely and more intense. Heatwaves come and go, but they also leave lasting scars on communities and economies alike. This new study shows the damage may be even deeper than we thought.

The researchers looked at data from early 25,000 adults in a longitudinal cohort in Taiwan over a 15-year period, from 2008 to 2022. Researchers used clinical biomarkers related to liver function, inflammation, and blood pressure to calculate each person’s biological age. Biological age acceleration (BAA) is simply biological age minus calendar age. Positive values mean you’re biologically “older” than expected, negative means you’re “younger”. They then looked at how heatwaves affected everyone’s biological age and mapped out heatwave exposure.

Studying Heatwaves in Our Bodies

A heatwave was defined in two ways: relatively, as two to four consecutive days hotter than the local 92.5th percentile, and absolutely, as at least three days above 36 °C (96.8 °F) or any single day above 38 °C (100.4 °F). This allowed them to capture both unusually hot spells for a given place and universally extreme temperatures.

People who experienced more heatwaves aged a little faster biologically. Over two years, that difference worked out to about 8–11 extra days of aging for those who were exposed to most heatwaves. It’s not that you suddenly wrinkle overnight, but your body quietly carries a heavier load. And for people working outdoors — like farmers and construction workers — the effect was stronger, adding up to nearly a month of extra aging for the same step up in exposure.

The researchers then divided all participants into four equal groups based on how many heatwaves they experienced. The lowest quartile is the 25% of people with the fewest heatwaves, and the highest quartile is the 25% with the most. For every interquartile-range increase in heatwave exposure (basically, going from a person who had fewer heatwaves to someone who had more within that middle spread), there were about 8–11 extra days of biological aging over two years.

“The study found that cumulative exposure to heatwaves accelerated ageing — the greater the cumulative exposure, the larger the acceleration in ageing,” wrote Paul J. Beggs, Environmental Health Scientist at Macquarie University, in an accompanying News & Views article.

Heatwaves Make You Older

Not everyone was affected the same.

Manual workers, rural residents, and people in communities with fewer air conditioners showed larger impacts. For manual workers, the effect rose to 0.090 years (about a month) per exposure step. Older adults, children, and those with chronic diseases also seemed to be disproportionately affected. But everyone was affected to some extent.

“We have a paradigm shift in our comprehension of the extent and gravity of heat’s impact on our health. The impact can occur at any age and can be lifelong,” adds Beggs.

The study didn’t analyze how this damage happens, but the researchers propose a few plausible mechanisms. High temperatures can shorten telomeres, promote oxidative DNA damage, and disrupt mitochondria. Obviously, when the “powerhouse of the cell suffers,” your entire body suffers.

There was, however, one silver lining. There seemed to be some adaptation over time. It’s not clear if this is owed to more air conditioners being installed or if people’s bodies adapted, but over the course of the study, the damage seemed to reduce somewhat.

But, at the end of the day, no matter how you look at it, this is bad news. It’s yet another consequence of heatwaves and yet another problem caused by climate change. Reducing exposure, whether at home, at work, or across our cities, is an important public health investment with lifelong dividends. Still, in the long run, as long as the climate continues to heat up, our bodies will continue to feel the effects.

The study was published in Nature.