Article image

Feeling the heat: Rising temperatures push the limits of the human body

A groundbreaking study is providing fascinating insights into the human body’s response to rising temperatures and intense heat. Led by Professor Lewis Halsey at the University of Roehampton, the research has revealed the existence of an upper critical temperature (UCT) for humans, falling somewhere within the range of 40°C to 50°C. 

This revelation indicates a tipping point at which the human body’s metabolic energy costs begin to surge in response to intense heat.

Understanding metabolic rates and their reactions to different conditions is an intricate science. The resting metabolic rate, which is the amount of energy that the human body requires to maintain basic, restful functioning, can in fact spike when people are subjected to environments that are hot and humid. 

“Quite a lot of work has been done on the range of temperatures that different animal species prefer to live at in terms of their metabolic rates being minimal and thus their energy expenditure being low, but, weirdly, information is much less available for humans when considering the upper limits of our thermal neutral zone,” explained Professor Halsey.

Implications of the study

The implications of this research extend across various sectors. Discerning the temperature thresholds at which human metabolic rates start to increase, and how this fluctuates amongst different individuals, could have a profound impact on areas such as work environments, sports, medical practices, and international travel. 

Professor Halsey emphasized the broader relevance of this study, stating that the research “provides fundamental knowledge about how we react to suboptimal environments, and how ‘optimal’ differs between people with different characteristics.”

Moreover, the research team is delving into how these extreme temperatures, those above the UCT, impact heart function, and how the effects vary among people with different traits, such as age and physical fitness. 

“We found some considerable changes in heart function responses to the heat between categories of people, the most novel being between the sexes,” said Professor Halsey. In other words, average men and women display distinctive differences in their cardiovascular responses to high heat levels.

How the research was conducted 

To investigate, the team used an advanced echocardiograph, a high-tech device that captures detailed images of heart function. This is not typical research equipment. “It was not easy to operate this kit in the heat! The sort of equipment you’d see in hospitals but rarely in research laboratories.”

As this research is ongoing, Professor Halsey will be presenting the most recent findings at the upcoming Society for Experimental Biology conference. “We are steadily building a picture about how the body responds to heat stress, how adaptable it can be, the limits to those adaptations, and – crucially – how varied responses are between individuals. In a warming world, this knowledge becomes ever more valuable.”

Indeed, as global temperatures continue to rise, the relevance and urgency of understanding our body’s responses to heat become more critical than ever. Professor Halsey’s research is helping to bridge this knowledge gap and shed light on the human body’s capabilities and limitations in the face of intense heat.

More about heat and the human body

The human body maintains an internal temperature of approximately 37 degrees Celsius (98.6 degrees Fahrenheit), a balance known as homeostasis. This balance can be affected by external temperature changes such as heat, which the body responds to in several ways to maintain its optimal temperature.


The body cools itself by sweating, which is water evaporating off the skin surface. The heat required to evaporate the water comes from the body, which thus reduces its temperature. This is why in hot weather, you tend to sweat more.


In response to heat, the blood vessels near the surface of your skin will dilate, or widen, in a process called vasodilation. This allows more blood to flow near the surface of the skin, which can help to radiate heat away from the body.

Increasing heart rate

To facilitate the process of heat loss, the heart rate increases to pump more blood through these dilated vessels.

Behavioral responses

The body can also signal that it’s too hot, leading to behavioral responses like seeking shade, removing clothing, or drinking cool liquids.

However, extreme heat can pose a danger to the body. Heat-related illnesses, such as heat stroke or heat exhaustion, can occur when the body can’t cool itself properly. These can be serious conditions that require medical attention. Symptoms can include heavy sweating, rapid pulse, dizziness, nausea, and confusion.

To prevent heat-related illnesses, it’s important to stay hydrated, take frequent breaks if you’re outside in the heat, and try to stay in cooler areas during the hottest parts of the day. If you or someone else is showing symptoms of a heat-related illness, it’s important to seek medical help right away.


Check us out on EarthSnap, a free app brought to you by Eric Ralls and

News coming your way
The biggest news about our planet delivered to you each day