July 3, 2025, 10:55 am | Read time: 5 minutes
Heat can become dangerous for the body. If the body’s own temperature regulation fails, it can be fatal in the worst-case scenario. High temperatures pose a health risk, especially for older people—or so it was long believed. However, data from Mexico indicate that young people are more at risk than previously thought.
In large parts of Germany, very high temperatures were recorded this week. The German Weather Service and news announcers advised staying indoors if possible due to the heat and high UV exposure. Such factors can cause circulatory collapse and heat damage, as FITBOOK explains here. Older people are at risk in extreme heat “simply because their perception of heat is limited,” according to a brochure from the Federal Ministry of Health on this topic.1 It is also well known that various physical abilities and protective functions decline with age. Nevertheless, a study from Mexico found that heat or a specific combination of temperature and humidity can be even more dangerous for a younger age group.2
Overview
- Study Shows Which Age Group Is Particularly Vulnerable to Heat
- Details of the Study
- Findings: High Temperatures Especially Deadly for Younger People
- Why Are So Many Young Adults and Small Children Among the Heat Deaths in Mexico?
- Older People Die More from Cold Than Heat
- Study Results Not Directly Applicable to Heat Mortality Risk in Germany
Study Shows Which Age Group Is Particularly Vulnerable to Heat
“Recent studies suggest that temperature-related mortality will be the greatest source of damage from climate change,” the study authors write in their introduction. In their current study, they examined Mexico—a country that experiences particularly extreme conditions due to hot and humid temperatures. The study initially assumed that older people have the highest risk of heat-related mortality. However, the results of their analysis contradict this assumption.
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Details of the Study
To better understand the relationships between high temperatures, especially high humidity, and increased mortality, the researchers analyzed data on deaths between 1998 and 2019. They registered more than 15 million deaths during this period, linking them with weather data and focusing on the combination of heat and humidity.
The “wet-bulb temperature” indicates the potential heat risk for humans in high humidity because it determines how well the body can cool itself through sweating.
The wet-bulb temperature is the lowest value to which a wet object can be cooled by evaporation at a given temperature and humidity. It is not identical to the air temperature we are familiar with but is a composite value of temperature and relative humidity.
In their analysis, the researchers considered factors such as the number of deaths between 1998 and 2019, weather data, and the combination of heat and humidity.
Findings: High Temperatures Especially Deadly for Younger People
Of the recorded deaths, a significant number involved individuals under 35 years old. A large percentage of them were between 18 and 35 years old. Study author Jeffrey Shrader described this in a press release as affecting “the most physiologically robust people in the population.” Affected were also children under five years old and infants.3
What combination of heat and humidity caused these deaths? According to the data, most deaths occurred at “wet-bulb temperatures” of 95 degrees Fahrenheit. The press release states that the critical threshold is 95 degrees Fahrenheit wet-bulb.
It should be noted again that the wet-bulb temperature is not identical to the air temperature we are familiar with but is a composite value of temperature and relative humidity. A wet-bulb temperature of, for example, 95 degrees Fahrenheit can occur at an air temperature of 95 degrees Fahrenheit with 35 to 40 percent humidity. You can use this calculator to determine the wet-bulb temperature in your area.
The researchers also examined the proportion of life lost. They found that young people under 35 years old accounted for a significant share of potential life lost due to early death. This is simply because, mathematically, young people lose more potential years of life from an early death than older people do.
Why Are So Many Young Adults and Children Among the Heat Deaths in Mexico?
According to the researchers, young children cannot regulate their body temperature as well as adults. They dehydrate faster and rely on the care of their surroundings. If caregivers recognize dangers too late, it can be fatal.
Older People Die More from Cold Than Heat
People aged 50 to 70 were surprisingly the least affected by heat-related deaths. The analyzed temperature and mortality data show that older people in Mexico are more likely to die from cold than heat. According to the press release, while Mexico experiences high heat, it also has high-altitude areas where it can get cold. Researchers explain that older people generally have a lower core body temperature, making them more sensitive to cold. As a result, they may spend more time indoors, where the risk of contracting infectious diseases is known to be higher than in the open air.
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Significance of the Study
While the issue of global warming is already receiving some attention, it is apparently not enough, the researchers warn. The calculations suggest that the potential years of life lost due to heat-related deaths among people under 35 will increase by more than 30 percent by the end of this century.
It is important to note various limitations. For example, the researchers assume that the behavior of the population in dealing with heat will change over time.
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Study Results Not Directly Applicable to Heat Mortality Risk in Germany
Mexico’s temperature and mortality data show that older people there are more sensitive to cold than heat. They may spend more time indoors, where the risk of infectious diseases is higher than in the open air. Therefore, the study results are not directly applicable to us. However, they are relevant in part—especially as an early warning signal of what could happen in Germany with advancing climate change.