When the Heat Also Heats the Head
There are days when a small annoyance is enough to trigger a disproportionate response. An argument over nothing, impatience in a line, difficulty concentrating… can coincide with soaring temperatures, like this summer's.
It's not accurate to say that heat "makes us aggressive," as if there were a biological anger switch. But science does accumulate growing evidence that high temperatures can disrupt sleep, attention, certain cognitive functions, mood, and the ability to regulate emotions.
The issue takes on another dimension when heat exposure ceases to be episodic and becomes prolonged. Because then the body not only tries to cool down, but it also has to keep the brain functioning, which requires quite precise physiological conditions.
The brain also pays the price for heat
The human body tries to maintain its internal temperature within a narrow range. When the environment heats up, sweating increases and blood flow distribution changes to favor heat loss, while the physiological effort required to maintain this balance also increases.
A review published in 2025 in Experimental Physiology examined studies on heat stress and hypoxia and found that, during hyperthermia, cerebral blood flow can decrease.
Although the authors caution that cognitive impairments cannot be explained solely by this mechanism, they also point out that heat stress appears to affect neural activity through additional pathways.
This helps explain why heat can interfere with functions we use all the time: attention, response speed, working memory, and information processing capacity.
A systematic review on indoor temperatures found that processing speed and reaction time appear to be among the cognitive functions most sensitive to increased temperature, although the authors caution that the evidence still has limitations.
When Thinking Becomes More Difficult
The problem isn't necessarily that the brain "shuts down." It's more accurate to note that certain tasks may require more effort while our ability to maintain the same accuracy and speed for extended periods decreases.
A 2024 review on temperature, cognition, affect, and behavior found associations between higher-than-usual ambient temperatures and conflict, as well as certain mental health problems.
However, its authors emphasize that this is still a developing field and that the effects depend on the exposure conditions.
The everyday consequences may seem insignificant: forgetting something, losing concentration, responding with less patience, or making a simple mistake. But when these small alterations accumulate during a workday, behind the wheel of a vehicle, or during an activity that requires quick decisions, they cease to be anecdotal and become a risk.
When nighttime temperatures remain high, the body has more difficulty dissipating heat and reaching the physiological conditions that promote restful sleep.
A study published in 2025 analyzed 9,153 older adults to examine the relationship between exposure to heat waves and sleep. Its results show the importance of sleep duration in the relationship between extreme heat and cognitive decline.
The connection is almost circular: heat, worse sleep, fatigue, reduced concentration, and decreased emotional regulation. Then another hot day arrives, and the brain begins the day without having fully recovered its resources.
More heat, more violence?
Irritability may therefore be less a direct effect of the temperature than the result of a chain of physiological and psychological processes. Fatigue, dehydration, fragmented sleep, physical discomfort, and greater effort required to perform daily tasks can reduce tolerance for minor frustrations.
A systematic review published in 2025 by researchers at King's College London examined the mechanisms that link extreme heat to mental health. It found evidence, albeit still limited, of psychological stress, sleep disturbances, fatigue, reduced physical activity, and changes in usual coping strategies.
But it's important to be careful when drawing cause-and-effect conclusions regarding heat, because a meta-analysis on temperature and behavior, with 80 effect sizes and 4,577 participants, did not find a reliable effect of temperature on prosocial or antisocial behaviors in the experiments analyzed.
The question becomes more complicated when observing entire populations. A systematic review and meta-analysis published in 2024 in Environmental Health Perspectives examined studies on temperature, crime, and violence, and found an association between rising temperatures and these outcomes, although the magnitude and characteristics of the relationship vary depending on the context.
More recently, a review published in 2025 also found a relationship between rising temperatures and violence. But the most recent evidence introduces an interesting correction: a study published in 2026 analyzed nearly one million amateur soccer matches in Germany and discovered an inverted U-shaped relationship; sanctioned actions increased up to around 13°C, but decreased when the heat was extreme. In other words, too much heat may not produce more aggression, but rather reduce physical activity itself.
The message is important: heat can alter behavior, but there is no formula that allows us to convert degrees Celsius into degrees of anger. The human brain does not respond to a thermometer mechanically.
Mental health in the spotlight
The concern is not limited to everyday irritability. A systematic review and meta-analysis published in January 2026 in npj Mental Health Research compiled 28 observational studies published between 2007-2025 on children, adolescents, and young adults up to 24 years of age.
Exposure to high temperatures was associated with a 13% increased risk of hospital visits or hospitalizations for mental disorders; a 14% increased risk of schizophrenia or other psychotic disorders; and an 18% increased risk of depression. The authors caution about the heterogeneity of the studies and the need for more evidence in low- and middle-income countries.
Another study published in July 2026 in Nature Health provides evidence from four countries—Brazil, Canada, Chile, and New Zealand. Analyzing 2,618,307 hospitalizations in 852 locations, researchers found that sustained extreme heat waves were associated with a 3.3% increase in the risk of hospitalization for mental and behavioral disorders on the same day and a 5.6% cumulative increase over the following eight days.
Cuba and the Heat
Cuba has a peculiarity that can be misleading: the population is accustomed to tropical heat. However, being accustomed to it does not mean being immune to its effects, especially when the intensity, duration, and frequency of extreme heat episodes increase.
Dr. Luis Lecha Estela, a Doctor of Geographical Sciences, Meritorious Researcher, and pioneer of biometeorological forecasting in Cuba, has studied the relationship between extreme weather conditions and health for decades. In statements published by Granma in 2025, he explained that decades of research in Villa Clara had identified intense episodes of heat stress capable of producing meteorotropic effects in vulnerable individuals.
Regarding the Cuban temperament and the heat, there’s no scientific evidence to suggest that the heat makes Cubans as a group more irritable, nor would it be accurate to attribute complex social behaviors to the climate.
What can be said is that Cubans are exposed to thermal conditions that can favor the same mechanisms observed internationally: physiological stress, fatigue, poor sleep, reduced concentration, and increased discomfort. Lecha himself has warned that the increase in temperatures and extreme weather events constitutes a growing problem for the health of the Cuban population.
Therefore, if someone reacts poorly on a sweltering day, the thermometer may be one piece of the puzzle, but not the complete explanation. Temperature, humidity, rest, health, environment, and social circumstances combine to produce something that meteorology alone cannot measure: mood.
The high temperatures, which are hitting hard this summer, don't just affect the skin. They can disrupt sleep, put more strain on the body, hinder certain cognitive tasks, and, in some people, increase psychological vulnerability.
Perhaps that's why it's best to stop talking about heat solely as a matter of comfort. When the thermometer rises too high, it can also change the way we think, rest, make decisions, and interact with others.
Translated by Amilkal Labañino / CubaSí Translation Staff
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