Why Do Some People Deal with Heat Better? A Deep Dive into Thermoregulation

October 1, 2025 •

4 min read

Studies have found that genetics play a relatively small role—around 5%—in explaining why some people deal with heat better. This means that for the majority of people, the ability to withstand high temperatures is heavily influenced by a mix of factors including lifestyle, physical condition, and environmental adaptation. Understanding this complex interplay is key to managing your own comfort and safety in the heat.

Quick Summary

An individual's ability to tolerate heat varies significantly due to a combination of physiological adaptations from acclimatization, body composition, fitness level, and hydration status, with a smaller genetic component.

Key Points

Genetics Play a Small Role: Genetic factors account for only a small portion of the differences in heat tolerance, suggesting that other elements are more impactful.
Acclimatization is Crucial: Regular, gradual exposure to heat effectively trains your body to cope better, improving your sweat response and cardiovascular function.
Fitness Enhances Efficiency: Higher cardiovascular fitness levels improve your body's ability to regulate temperature, allowing for more efficient cooling.
Body Fat Insulates: Individuals with a higher body fat percentage may find it harder to dissipate heat, as fat acts as an insulator, trapping heat inside the body.
Hydration is Key to Sweating: Staying properly hydrated is essential for maintaining a healthy blood volume and enabling your body's sweating mechanism to function effectively.
Age and Health Conditions are Factors: Both the very young and older adults, as well as those with chronic illnesses, have a diminished capacity to tolerate heat.
Lifestyle Habits Matter: Factors like hydration, alcohol use, and certain medications can also negatively affect your body's ability to regulate temperature.

During a heatwave, you may have noticed that some people seem unfazed while you're struggling. This difference isn't just about personal preference; it's a matter of complex physiological and environmental factors that govern your body's response to heat. The human body is equipped with sophisticated mechanisms to maintain a stable core temperature, but the efficiency of these systems varies from person to person. Genetics, while a factor, are far from the whole story, with other elements like acclimatization and fitness playing a much larger role.

The Core Mechanisms of Thermoregulation

At its heart, dealing with heat is about thermoregulation—the body's process for balancing heat production and heat loss. The two primary cooling methods are:

Sweating: As sweat evaporates from your skin, it draws heat away from your body, providing a powerful cooling effect. The efficiency and amount of sweat produced can vary significantly between individuals and can be improved through acclimatization.
Vasodilation: When the body gets hot, blood vessels near the skin's surface widen (dilate) to increase blood flow. This allows heat to be transferred from the body's core to the surface, where it can be more easily released into the surrounding air.

The Role of Acclimatization and Genetics

While we may be born with a certain predisposition, our bodies are remarkably adaptive. Acclimatization is the process by which a person's body adjusts to a new climate over time.

The Adaptations of Acclimatization

When a person is regularly exposed to heat, their body becomes more efficient at cooling itself through several key changes:

Increased Sweat Rate and Efficiency: The body learns to begin sweating earlier and produce a greater volume of sweat, allowing for a more rapid and effective cooling response.
More Dilute Sweat: Over time, the body becomes more adept at reabsorbing sodium from sweat. This results in less salty sweat, which helps conserve electrolytes and makes the sweat evaporate more easily.
Lowered Heart Rate: Acclimatization improves cardiovascular efficiency, meaning the heart doesn't have to work as hard to pump blood and dissipate heat. This results in a lower heart rate during heat exposure.

The Genetic Factor

AncestryDNA research indicates that genetics account for only a small percentage of an individual's heat tolerance differences. However, ancestral climate can influence certain physiological traits, like body size and proportion, that affect how a person responds to heat. For example, populations from historically hotter climates may have evolved with different proportions to maximize heat loss.

Fitness and Body Composition

An individual's physical condition has a significant impact on their heat tolerance. Cardiovascular fitness and the amount of body fat are two key components.

Fitness Levels and Heat Tolerance

Fitter individuals tend to cope with heat better than their less-fit counterparts. This is because:

Efficient Circulation: High aerobic fitness allows the body to move blood to the skin for cooling without overly straining the heart.
Improved Sweating: Fit individuals often sweat more efficiently, allowing them to cool down faster during physical activity in the heat.

Body Fat and Insulation

Body fat acts as an insulator, trapping heat inside the body. This makes it harder for individuals with higher body fat percentages to dissipate heat, leading them to feel warmer and potentially sweat more profusely. Conversely, leaner individuals, especially those with a larger surface area relative to their mass, tend to cool down more easily.

The Critical Role of Hydration

Proper hydration is non-negotiable for anyone operating in the heat, regardless of their natural tolerance. Dehydration severely impairs the body's ability to sweat and regulate its temperature, significantly increasing the risk of heat-related illnesses. Drinking sufficient fluids allows the body to maintain the necessary blood volume and sweat production needed for effective cooling.

Other Modulating Factors

Beyond the major physiological factors, several other elements can influence how well someone handles the heat:

Age: The very young and the elderly are particularly vulnerable to heat stress due to less efficient thermoregulatory systems.
Chronic Health Conditions: Conditions like diabetes, heart disease, and hypertension can impair the body's heat-dissipating mechanisms.
Medications: Certain medications, including diuretics, antihistamines, and some psychiatric drugs, can interfere with temperature regulation.
Alcohol and Drugs: Alcohol use, in particular, can impair the body's ability to regulate temperature.

Comparison of Factors Influencing Heat Tolerance


Factor	Impact on Heat Tolerance	Mechanism	Modifiable?
Acclimatization	Significantly high	Improves sweat rate, cardiovascular efficiency, and blood flow to the skin	Yes
Fitness Level	Significantly high	Allows heart to work more efficiently, improves sweat response	Yes
Body Composition	Moderately high	Body fat acts as an insulator, hindering heat dissipation	Yes
Hydration Status	Critically high	Enables efficient sweating, crucial for temperature regulation	Yes
Genetics	Relatively low	Influences subtle aspects like body shape and inherent sweat efficiency	No
Age	Moderate	Thermoregulatory systems are less efficient in the very young and old	No
Health Conditions	Moderate to high	Can impair cardiovascular function and sweat production	Partially

Conclusion

Ultimately, a person's ability to deal with heat is not a fixed trait but a dynamic combination of biological and environmental factors. While genetics set a baseline, the most influential elements are our capacity for acclimatization, our level of fitness, and our day-to-day hydration habits. By understanding these components, we can better appreciate individual differences and take proactive steps to improve our own heat tolerance and safety. Embracing healthy lifestyle choices and gradually preparing for warmer conditions are the most effective strategies for staying cool when the temperature rises.

For more in-depth reading on human adaptation to environmental changes, consider exploring research available through reputable sources such as the National Institutes of Health.

Frequently Asked Questions

Yes, you can significantly improve your heat tolerance through a process called acclimatization. By gradually increasing your time and activity levels in warm environments over a period of 7 to 14 days, your body adapts by improving its sweating efficiency and cardiovascular response.

Body composition plays a key role, particularly the ratio of body fat to muscle. Body fat acts as an insulator, trapping heat, which makes it harder for the body to cool down. Individuals with less body fat generally dissipate heat more easily.

Yes, both young children and older adults have a diminished ability to regulate their body temperature. This makes them more susceptible to heat stress and requires extra precautions during hot weather.

Genetics are a minor factor, accounting for only about 5% of the variation in heat tolerance between individuals. While ancestral climate can influence certain body features that affect heat response, acclimatization and fitness are far more influential.

Yes, high cardiovascular fitness improves heat tolerance. Fitter people have a more efficient circulatory system, allowing them to move heat from their core to their skin more effectively. They also tend to sweat earlier and more profusely.

Dehydration critically impairs your body's ability to cool itself. Without sufficient fluid, your body cannot produce enough sweat, which is its primary method for shedding heat. This increases your risk of heat-related illnesses.

Yes, certain medications like diuretics and antihistamines, as well as chronic health conditions such as diabetes and heart disease, can interfere with your body's natural temperature regulation and increase your vulnerability to heat stress.