There’s also some debate among scientists about whether epigenetic clocks are the best measure for aging, said Rachel Morello-Frosch, an environmental health scientist at the University of California, Berkeley. How to best measure biomarkers, and how to use them to predict future health, is an “evolving space in the scientific field,” she said.

Epigenetic changes aren’t necessarily bad, either, and the study doesn’t clarify whether they could reflect positive adaptations to heat instead of negative ones, said Greg Wellenius, an environmental epidemiologist at Boston University School of Public Health. People in hotter areas may have acclimatized to the heat, potentially by spending more time indoors, he said. But just “indicating that there is a quantifiable change at the cellular level” is a step toward understanding heat’s effect on the body, he said.

Experts say there are still many questions left to answer: How might things like air conditioning affect epigenetic aging? Can short visits to hotter areas cause you to age faster? Can moving away from hotter areas reverse it?

Because the analysis was based on a single blood sample from each subject, “we don’t really have that kind of longitudinal data” yet, said Jennifer Ailshire, a professor of gerontology and sociology at the U.S.C. Leonard Davis School of Gerontology and the other author of the study.

This study may open the door to future research into how interventions, like air conditioning or more shade, could stave off the adverse effects of aging, said Mariana Arcaya, a professor of urban planning and public health at the Massachusetts Institute of Technology.

“Right now, the literature is very focused on, ‘Can you survive in extreme heat without medical intervention?’” she said. This study, in contrast, suggests that even if people aren’t at immediate risk of health crises or death because of the heat, “there may still be an effect.”