We usually think of aging as something measured in birthdays. Every year adds another number to our lives, and we assume our bodies grow older at roughly the same pace.

But what if the climate around us is quietly influencing how quickly our cells age?

A scientific study published in Science Advances suggests that long-term exposure to extreme heat may accelerate biological aging, potentially leaving people in hotter environments biologically older than people of the same chronological age living in cooler regions.

Researchers from the University of Southern California examined 3,686 American adults aged 56 and older, comparing their blood-based aging markers with years of temperature and humidity records.

The findings were striking.

People living in areas experiencing frequent high-heat days showed molecular patterns associated with faster aging. In one widely reported comparison, people exposed to at least 140 hot days annually exhibited approximately 14 additional months of biological aging compared with those living in areas experiencing fewer than 10 such days.

The results raise a troubling possibility: extreme heat may affect the body in ways that extend beyond dehydration, heat exhaustion, or heatstroke.

And as global temperatures rise, the implications could be significant for millions of older adults.

A Study of 3,686 Adults Links Extreme Heat to Faster Biological Aging

The research, titled Ambient outdoor heat and accelerated epigenetic aging among older adults in the US, was published on February 26, 2025.

It was conducted by Eun Young Choi and Jennifer A. Ailshire of the University of Southern California's Leonard Davis School of Gerontology.

The researchers used data from the nationally representative US Health and Retirement Study, which follows older Americans to better understand aging, health, and economic circumstances.

Their investigation connected two types of information that are rarely examined together: environmental heat exposure and molecular indicators of aging.

The research at a glance

Adults studied

3,686

Minimum age

56+

Climate-data period

2010–2016

Reported age difference

~14 months

Study: Choi and Ailshire, Science Advances (2025). The 14-month figure refers to an estimated epigenetic-aging difference, not proven life expectancy lost.

How Scientists Conducted the Research

Researchers analyzed DNA methylation patterns from participants' blood samples.

They then compared these biological measurements with local heat-index records, examining exposure over periods ranging from the preceding days to the previous six years.

The analysis accounted for several potentially influential characteristics, including age, sex, education, household wealth, smoking, alcohol consumption, physical activity, obesity, neighborhood vulnerability, and air pollution.

Even after these statistical adjustments, greater heat exposure remained associated with accelerated epigenetic aging.

The finding suggests that chronic environmental heat may be relevant to how the body ages at the molecular level.

It does not establish that heat exposure directly caused the observed changes, but it provides a foundation for further investigation.

What Is Biological Aging, and How Is It Different From Your Actual Age?

Most people understand chronological age.

If you were born 60 years ago, your chronological age is 60.

Biological age is different.

It attempts to measure the condition of the body's cells and biological systems rather than simply counting the years since birth.

Two people who are both 65 may have very different cardiovascular health, metabolic function, inflammatory profiles, and cellular characteristics.

One may remain physically active with relatively healthy organs, while the other may already be experiencing significant age-related changes.

Biological aging research attempts to measure these differences.

Chronological Age vs. Biological Age

Biological age is not one universally agreed measurement. Different methods capture different aspects of aging, and their results do not always match.

The USC study used several established DNA methylation-based methods to investigate these patterns.

DNA Methylation: How Scientists Look for Signs of Aging Inside Cells

At the center of this research is a process called DNA methylation.

DNA contains the genetic instructions used by our cells, but genes are not active at the same level all the time.

Cells have molecular mechanisms that help regulate when and how genes are expressed.

DNA methylation is one of them.

It involves attaching small chemical groups, known as methyl groups, to particular locations on DNA.

These chemical markers can influence gene regulation without changing the underlying DNA sequence.

Why DNA Methylation Matters for Aging

As people grow older, patterns of DNA methylation tend to change.

Some locations become more methylated. Others become less methylated.

Researchers have discovered that these changes can provide useful information about aging and age-related health risks.

By analyzing thousands of methylation sites, scientists can develop statistical models called epigenetic clocks.

These models estimate biological age or other characteristics associated with aging.

The USC researchers used three such measures:

• PCPhenoAge: An epigenetic measure associated with physiological aging and health-related characteristics.
• PCGrimAge: A measure developed to predict mortality-related risks using DNA methylation patterns.
• DunedinPACE: A method designed to estimate the pace of biological aging.

The study found that longer-term heat exposure was associated with changes across all three measures, although the size and interpretation of the effects differed.

Living With Frequent Extreme Heat Was Linked to Additional Biological Aging

One of the study's most widely discussed findings involves the difference between living in relatively cool and consistently hot locations.

According to the University of Southern California's explanation of the research, older adults living in areas with at least 140 days of high heat annually showed approximately 14 months of additional biological aging compared with those in areas with fewer than 10 such days.

That comparison helps illustrate the potential scale of the association.

But it requires careful interpretation.

The researchers did not demonstrate that experiencing 140 hot days literally removes 14 months from someone's remaining lifespan.

Instead, the difference was measured through DNA methylation patterns that researchers associate with biological aging.

Those are related concepts, but they are not interchangeable.

Different Epigenetic Clocks Showed Different Results

The published study reported several associations depending on the heat-exposure period and biological-aging measure.

For example, longer-term exposure was associated with an estimated 2.48-year increase in PCPhenoAge acceleration in one model and a 1.09-year increase in PCGrimAge acceleration in another.

DunedinPACE also indicated a faster estimated rate of biological aging with longer-term heat exposure.

These findings should not be added together or interpreted as a direct prediction of years of life lost.

They reflect separate statistical measures of biological aging.Why Humidity Makes Extreme Heat More Dangerous.

Temperature alone does not determine how stressful hot weather is for the human body.

Humidity also matters.

The USC researchers used the heat index, which combines air temperature and relative humidity to estimate how hot conditions feel to people.

This distinction is especially important in humid climates.

When the air contains substantial moisture, sweat evaporates less efficiently from the skin.

Because evaporation is one of the body's main cooling mechanisms, humid conditions can make it harder to release excess heat.

A Heat Index Above 90°F Signals Elevated Risk

The study examined categories based on US National Weather Service heat-index thresholds.

A heat index around 90°F, equivalent to approximately 32.2°C, is within the National Weather Service's Extreme Caution category.

That is different from simply recording an air temperature of 90°F.

For example, an air temperature below 90°F can still produce a heat index above that level when humidity is sufficiently high.

The researchers were interested in cumulative heat stress as measured through these conditions, rather than temperature readings alone.How Could Extreme Heat Accelerate Aging?

The study identified an association, but it did not establish precisely which biological processes caused the changes.

However, scientists already know that prolonged heat exposure places significant demands on human physiology.

Several mechanisms could plausibly help explain the relationship.

1. Repeated Heat Stress Challenges the Body

The human body works continuously to maintain its internal temperature within a narrow range.

During hot weather, it increases blood flow toward the skin and produces sweat to release heat.

These responses require physiological adjustments.

When temperatures remain high for extended periods, especially overnight, the body may have fewer opportunities to recover.

Researchers suspect that repeated thermal stress could contribute to longer-term biological changes.

2. Heat Can Increase Cardiovascular Strain

During periods of intense heat, the heart often works harder to circulate blood toward the skin.

Dehydration may further affect blood volume and cardiovascular function.

For people with existing cardiovascular conditions, the added strain can become particularly dangerous.

Researchers are investigating whether repeated exposure to these stresses contributes to longer-term changes associated with aging.

3. Heat Can Affect Inflammation and Cellular Stress

Extreme heat may influence inflammatory signaling, oxidative stress, and cellular repair processes.

Inflammation and oxidative damage are already important areas of aging research.

Experimental studies also suggest that temperature stress can influence gene regulation and epigenetic processes.

However, the precise pathway linking ambient heat to DNA methylation patterns in human blood remains uncertain.

The USC findings are consistent with the possibility of cumulative biological effects, but they do not prove which mechanisms are responsible.

4. Dehydration and Kidney Stress May Contribute

High temperatures increase fluid loss through sweating.

If that fluid is not replaced, dehydration can affect circulation and kidney function.

Severe or repeated heat stress can also contribute to kidney injury in susceptible individuals.

These effects are relevant to understanding the broader health burden of heat.

But the study did not show that dehydration or kidney damage specifically mediated its epigenetic-aging results.

Why Older Adults May Be Particularly Vulnerable to Extreme Heat

The USC study focused on adults aged 56 and older.

That population matters because several physiological changes associated with aging can influence the body's response to high temperatures.

Older adults may experience reduced sweating efficiency, changes in skin blood flow, decreased thirst sensation, or medical conditions that complicate temperature regulation.

Some medications can also affect hydration, circulation, or heat tolerance.

However, the study's subgroup analyses did not provide strong evidence that the heat-aging association was substantially greater in specific sociodemographic groups.

That means the findings should not be exaggerated into a claim that researchers established exactly which demographic groups experience the fastest heat-related biological aging.

Could Climate Change Make Biological Aging a Bigger Public Health Concern?

Heatwaves have long been recognized as dangerous because they can increase the risk of heatstroke, cardiovascular complications, dehydration, and heat-related death.

The USC research raises another possibility.

If chronic environmental heat influences biological aging, then the consequences of increasingly hot environments may accumulate over years rather than appearing only during extreme weather emergencies.

This makes the research particularly relevant to cities where summer temperatures remain high for long periods.

Urban Heat Islands Can Increase Exposure

Urban environments can retain substantial heat because of paved surfaces, buildings, limited vegetation, and human activity.

This phenomenon is known as the urban heat island effect.

Neighborhoods with fewer trees and more heat-absorbing surfaces may experience higher temperatures than nearby green spaces.

Residents without adequate cooling may face additional exposure, especially during warm nights.

These environmental inequalities are relevant to public health planning, even though the USC study did not directly establish the separate biological-aging effects of each neighborhood feature.

Hotter Cities May Need More Age-Friendly Infrastructure

Researchers have suggested that heat adaptation should receive greater attention in urban planning.

Possible strategies include expanding tree cover, developing shaded public spaces, improving building design, and ensuring access to safe cooling environments.

Jennifer Ailshire emphasized the need for better heat-mitigation strategies as populations age and environmental temperatures rise.

Can Air Conditioning Protect Against Heat-Related Biological Aging?

Air conditioning can reduce indoor heat exposure and help prevent acute heat-related illness.

That makes access to effective cooling an important public health consideration.

However, the USC study relied primarily on neighborhood outdoor heat estimates.

It did not directly measure each participant's personal heat exposure throughout the day.

Nor did it fully establish how factors such as air-conditioning use, time spent indoors, building insulation, or workplace conditions altered individual biological-aging patterns.

Consequently, the research cannot determine exactly how much air conditioning would reduce the epigenetic-aging association.

Cooling environments are a sensible heat-safety measure, but this particular study did not demonstrate that air conditioning prevents accelerated biological aging.

What the Study Does Not Prove

The findings are important, but several limitations deserve attention.

It Was Observational Research

Researchers examined associations between existing heat records and biological measurements.

They did not randomly assign participants to live in hot or cool environments.

As a result, differences between geographic locations could still reflect influences not fully captured by statistical adjustments.

Outdoor Heat Is Not the Same as Personal Exposure

Two people living in the same neighborhood may experience very different levels of heat.

One might work outdoors, while another spends most of the day in a cooled building.

The study's geographic exposure estimates cannot fully capture that variation.

Epigenetic Age Is Not a Direct Measurement of Lifespan

DNA methylation clocks are valuable research tools, but they do not function as exact predictions of how long someone will live.

An estimated 14-month difference in biological age should not be presented as proof that a person will die 14 months earlier.

The Study Focused on Older Americans

The findings cannot automatically be generalized to children, younger adults, or all populations worldwide.

Climate, housing quality, healthcare access, genetics, and daily behavior differ considerably across regions.

These limitations do not invalidate the research.

They help define what scientists can reasonably conclude from it.

How to Reduce the Health Risks of Prolonged Heat

Although researchers have not yet established that particular interventions prevent heat-associated changes in epigenetic age, practical steps can reduce the immediate dangers of hot weather.

These are especially important for older adults and people with underlying medical conditions.

• Stay in cooler environments: Use air conditioning or accessible cooling centers during dangerous heat.
• Maintain adequate hydration: Drink fluids regularly unless a healthcare professional has advised fluid restrictions.
• Avoid unnecessary exertion during peak heat: Schedule demanding outdoor activities for cooler hours when possible.
• Monitor heat-index warnings: Consider humidity as well as temperature.
• Keep indoor spaces cooler: Use shading, ventilation when appropriate, and measures that reduce solar heat gain.
• Check on vulnerable people: Older adults and individuals with medical conditions may need additional assistance during heatwaves.

Fans can improve comfort in some circumstances, but may be inadequate or unsafe as the only cooling method during very high indoor temperatures.

Anyone experiencing confusion, collapse, or signs of heatstroke requires urgent medical attention.

What This Research Means for Countries With Hot, Humid Climates

The findings are relevant beyond the United States.

Countries with prolonged hot seasons and high humidity face the same fundamental challenge of helping people maintain safe body temperatures.

In South Asia, for example, large populations experience frequent combinations of high temperatures and humidity.

Cities such as Dhaka can also experience localized heat retention because of dense construction, traffic, limited greenery, and varying access to cooling.

But the USC study did not directly measure biological aging among Bangladeshi residents.

It would therefore be premature to assign the same estimated 14-month difference to people living in Dhaka or other tropical cities.

What the study does suggest is that long-term heat exposure deserves greater attention as a potential influence on healthy aging, particularly in regions where extreme heat is becoming more frequent or persistent.

Key Findings From the Extreme Heat and Aging Study

Based on Choi and Ailshire, Science Advances (2025), and USC's published explanation of the study.

Frequently Asked Questions About Heat and Biological Aging

Can extreme heat make you age faster?

A 2025 study found that older adults living in hotter areas showed greater epigenetic-age acceleration than those in cooler locations. The findings suggest a possible link between chronic heat and biological aging, but do not establish direct causation.

How much faster can heat make you age?

One reported comparison found approximately 14 additional months of estimated biological aging among people experiencing at least 140 high-heat days annually, compared with those in areas with fewer than 10. This does not mean 14 months of life expectancy were lost.

What is an epigenetic clock?

An epigenetic clock is a statistical model that uses DNA methylation patterns to estimate biological age or the pace of aging. Different clocks measure different aging-related characteristics.

Does air conditioning prevent premature aging?

Air conditioning reduces heat exposure and can protect against heat-related illness. However, there is not enough evidence from this study to conclude that air conditioning directly prevents accelerated epigenetic aging.

Extreme Heat May Be Changing More Than How We Feel

For years, public health discussions about extreme heat have focused on immediate dangers: dehydration, exhaustion, heatstroke, and increased mortality during heatwaves.

The USC research suggests the story may be more complicated.

By examining thousands of older adults and comparing environmental temperatures with DNA methylation patterns, researchers found evidence that prolonged exposure to high heat is associated with faster biological aging.

The estimated differences were substantial in some comparisons, including the widely reported figure of approximately 14 additional months of epigenetic age.

But these findings are not proof that extreme heat directly shortens life by the same amount.

They are evidence that the environment may leave measurable biological signatures associated with aging.

That distinction matters scientifically, and it also makes the research more intriguing.

Aging is influenced by genetics, health, behavior, and social circumstances. Studies like this suggest that the climate people live in may deserve a place in that conversation too.

As heatwaves intensify and populations grow older, researchers will need to determine whether these molecular changes lead to measurable differences in disease, disability, and longevity—and whether better cooling and environmental protections can reduce the risk.

The larger lesson is that protecting people from extreme heat may be important not only for surviving dangerous summer days, but also for supporting healthier lives over the long term.

For now, the most practical response is clear: take heat warnings seriously, protect people at increased risk, and support communities in creating safer, cooler environments.