Every day, Kalpana Suryawanshi, 48, looks into the mirror and whispers, “I look older than my age.” Eight years ago, she was diagnosed with Type 2 diabetes. Since then, her health has deteriorated, which she attributes to increased exposure to heat while working in the fields, planting crops, harvesting produce, and carrying heavy loads of cattle fodder. During this time, she frequently experienced dizziness and weakness as temperatures exceeded 40 degrees Celsius in her village of Nandani in Maharashtra state, India.

Heat is known to affect cognitive function, cardiovascular health, and kidney function, and a growing body of research suggests that exposure to rising temperatures also accelerates the body’s aging process. A 2023 German study published in Environment International was the first to find that higher air temperatures are associated with faster aging at the cellular level. It found that prolonged exposure to elevated temperatures can make the body age faster than its chronological age, a phenomenon known as epigenetic age acceleration. Scientists measure this process using epigenetic clocks, which analyze chemical markers called DNA methylation that turn genes on and off. The study found that in areas where the average annual temperature is 1°C higher, people tend to show signs of accelerated aging at the cellular level.

When scientists talk about epigenetic age, they measure how old a body is at the cellular level, which can differ from the actual age in years. This is based on changes to DNA called epigenetic markers, the chemical tags that turn genes on or off. Environment, lifestyle, and stress influence these markers. As one ages, the pattern of these chemical tags changes, and scientists use this information to create an epigenetic clock, a tool that estimates biological age.

The genes affected by these changes control many vital functions, like repairing cells and tissues and protecting against toxins. When the wrong genes are switched on or off, it can make it harder for the body to repair itself, fight disease, or recover from stress. Over time, these hidden changes can lead to outward signs of aging, such as weaker bones or slower healing. Epigenetic age gives a glimpse into how well the body is holding up on the inside.

2024 was the hottest year on record, with 6.8 billion people worldwide experiencing extreme heat for at least 31 days. One unusual effect of this rising heat is observed firsthand by India’s community health care workers, who report that more people appear older than their actual age.