Does summer change the brain? How heat influences mood, concentration and productivity

Does summer change the brain? How heat influences mood, concentration and productivity

High temperatures do not just affect the body. Discover how heat influences the brain, alters mood, reduces concentration and can compromise productivity and mental health.

When temperatures rise, the brain changes pace

There are days when everything seems to require extra effort. Concentration wanes, patience quickly runs out and simple tasks take longer to complete. Many people put these feelings down to tiredness or routine, but there is another factor that is often overlooked: heat.

Although we commonly associate high temperatures with risks such as dehydration, heatstroke or sunburn, science shows that heat also affects how the brain functions. The ability to concentrate, memory, speed of reasoning, decision-making and even the way we regulate our emotions can all be influenced by the ambient temperature.

This is particularly important at a time when heatwaves are becoming increasingly frequent. The Intergovernmental Panel on Climate Change (IPCC) predicts that episodes of extreme heat will increase in frequency, duration and intensity over the coming decades, posing new challenges for public health (IPCC, 2023). The World Health Organization (WHO) therefore considers extreme heat one of the greatest environmental threats to human health, warning of its effects on both the body and mental health (WHO, 2021).

In recent years, researchers in neuroscience, physiology and psychology have sought to understand how heat interferes with brain function. Their findings are consistent: high temperatures force the body to work harder to maintain its internal balance, reducing the efficiency of essential cognitive processes (Hancock & Vasmatzidis, 2003; Gaoua, 2010).

The brain: an organ highly sensitive to temperature

Despite accounting for only around 2% of body weight, the brain consumes approximately one fifth of all the energy produced by the body. This intense metabolic activity generates heat continuously, which is why brain temperature must remain within very narrow limits to ensure that it functions properly.

The structure primarily responsible for this regulation is the hypothalamus, a small structure located at the base of the brain that acts as a true "biological thermostat". Whenever body temperature rises, the hypothalamus triggers mechanisms designed to dissipate heat, such as increased sweating, the dilation of blood vessels and faster peripheral circulation.

Although these mechanisms are essential to prevent the body from overheating, they require significant physiological effort. Some of the energy resources that would normally be available for cognitive functions are instead used to keep body temperature stable.

According to Hancock and Vasmatzidis (2003), this redistribution of resources helps explain why tasks requiring concentration, memory or complex reasoning become progressively more difficult during periods of intense heat.

Dehydration begins long before thirst

One of the biggest misconceptions is that only severe dehydration impairs the brain. In reality, even a slight reduction in body water is enough for cognitive performance to begin to decline.

In a classic study published in the International Journal of Psychophysiology, Cian and colleagues (2001) demonstrated that water losses equivalent to just 1–2% of body weight are enough to cause measurable changes in attention, short-term memory and information-processing speed.

These effects can occur even before thirst develops. This means that many people begin an afternoon of work or study already experiencing a fluid deficit capable of reducing their intellectual performance, without being aware of it.

The most common symptoms include:

• difficulty maintaining concentration;
• a feeling of mental fatigue;
• slower reasoning;
• headaches;
• reduced problem-solving ability.

Although often attributed to tiredness, these signs may simply reflect inadequate hydration.

Why do we feel that "the brain slows down"?

Every day, the brain carries out thousands of processes simultaneously: it interprets sensory information, controls movement, regulates emotions and coordinates vital functions. To perform all these tasks, it needs a continuous supply of oxygen, glucose and water.

As temperatures rise, the body enters a state of constant adaptation. Blood circulation changes, sweating increases and the energy consumed by thermoregulation rises. As a result, less energy remains available for complex cognitive processes.

In practice, this means that the brain continues to function, but does so less efficiently. This is why routine activities, such as writing a report, studying for an exam or taking part in a meeting, seem to require much more effort during a heatwave.

This feeling is not the result of a lack of motivation or laziness. It is a perfectly normal physiological response to an environment that forces the body to work harder to preserve its internal balance.

But the impact of heat does not end here. The changes it causes in brain activity also affect how we feel, react and relate to others. It is precisely this connection between temperature, emotions and mental health that we will explore in the next part of this article.

Does heat alter mood? Science says yes

Who has not heard someone say that "the heat is making them lose patience"? Although this is an everyday expression, there is in fact a biological explanation for this change in behaviour. Heat does not just affect physical comfort; it also interferes with the brain mechanisms responsible for regulating emotions.

When body temperature rises, the body enters a state of greater physiological demand. The brain needs to coordinate heat dissipation, maintain stable blood pressure, control hydration and ensure that the organs continue to function normally. This ongoing effort reduces the resources available for other functions, particularly those that allow us to control impulses, manage emotions and respond thoughtfully to stressful situations.

According to Gaoua (2010), high temperatures reduce the efficiency of executive functions, located mainly in the prefrontal cortex, the region of the brain responsible for self-control, decision-making and emotional regulation. As a result, minor setbacks may be perceived as more intense and provoke disproportionate reactions.

Why do we lose patience more easily?

The discomfort caused by heat acts as a constant stressor. Excessive sweating, feelings of fatigue, difficulty finding a comfortable temperature and the constant effort to keep the body in balance create a physiological burden that reduces tolerance of frustration.

This is why, during a heatwave, ordinary situations — a traffic jam, a transport delay or a computer problem — can trigger irritation much more quickly than on days with mild temperatures.

Research in environmental psychology shows that thermally uncomfortable environments increase perceived effort and reduce the ability to cope with negative events. In practical terms, the brain becomes less efficient at "filtering" unpleasant emotions and controlling impulsive responses.

Is there a link between heat and aggression?

Over recent decades, several studies have analysed the association between ambient temperature and aggressive behaviour. Although aggression depends on multiple social, cultural and individual factors, researchers have observed that episodes of violence tend to increase during periods of extreme heat.

One of the most widely accepted explanations is that prolonged heat lowers the threshold of emotional tolerance. When the body is already under pressure to maintain its temperature, the ability to inhibit impulses and rationally assess certain situations decreases.

This does not mean that heat turns a calm person into an aggressive one. Rather, it means that heat amplifies emotional reactions in individuals already exposed to stressors, increasing the likelihood of interpersonal conflict.

Anxiety: when heat mimics the symptoms of an anxiety attack

People living with anxiety disorders frequently report a worsening of symptoms during summer. The explanation lies in the fact that many physiological responses to heat are similar to those observed during an anxiety attack.

These include:

• increased heart rate;
• heavy sweating;
• rapid breathing;
• feeling dizzy;
• weakness;
• difficulty breathing deeply.

For someone predisposed to anxiety, these signs may be interpreted as indicators of danger. The brain responds by further heightening its state of alertness, creating a cycle in which physical symptoms fuel anxiety and anxiety intensifies physical symptoms.

This phenomenon explains why some people report more panic attacks during periods of intense heat, especially when they remain in poorly ventilated or very humid environments.

The impact on people with depression

Despite the positive image associated with summer, not everyone experiences an improvement in their mood during this season.

Extreme heat can worsen depressive symptoms through various mechanisms. Physical fatigue, reduced sleep quality, difficulty concentrating and the isolation caused by high temperatures all contribute to greater emotional strain.

In addition, some people reduce their physical activity during heatwaves, spending more time indoors. This change in routine can intensify feelings of demotivation and reduce psychological well-being.

The World Health Organization warns that individuals with pre-existing mental illnesses are among the groups most vulnerable to the effects of extreme temperatures and should be monitored particularly closely during the summer months (WHO, 2021).

Heat and sleep: when sleep no longer restores the brain

Sleep is one of the most important processes for brain health. During deep sleep, the brain consolidates memories, reorganises information and eliminates substances resulting from neuronal activity.

However, for this process to take place properly, body temperature needs to fall slightly.

When nights remain too warm, the body struggles to achieve this drop in temperature, delaying the onset of sleep and reducing the quality of rest.

A study published in the journal Science Advances demonstrated that high night-time temperatures significantly reduce sleep duration, particularly in older people and those living in urban areas, where the so-called "heat island effect" keeps buildings warmer at night (Obradovich et al., 2018).

Sleeping less or sleeping poorly leads, the following day, to:

• greater irritability;
• reduced ability to concentrate;
• poorer memory;
• less creativity;
• increased mental fatigue;
• lower productivity.

In many cases, what we attribute to the heat felt during the day is actually the result of an accumulation of poor nights' sleep.

Heatwaves and mental health: a new public health challenge

As climate change intensifies extreme weather events, concern about their psychological impacts is also growing.

The Lancet Countdown on Health and Climate Change report (Romanello et al., 2023) shows that heatwaves are associated with an increase in hospital admissions related to psychiatric disorders, anxiety, depression and behavioural changes.

At the same time, the IPCC warns that extreme heat poses a growing risk to the mental health of populations, not only because of its physiological effects, but also because of the social impact of climate change, including insecurity, isolation and reduced quality of life (IPCC, 2023).

Against this backdrop, it becomes clear that protecting health during summer does not simply mean avoiding sunburn or staying well hydrated. It also means recognising that the brain is one of the organs most sensitive to high temperatures and that caring for mental health must form part of strategies for adapting to new climatic conditions.

How heat reduces concentration and productivity

If there is one common complaint during summer, it is difficulty maintaining concentration. Tasks that are usually simple begin to require more time, more effort and more breaks. Although it is tempting to attribute this drop in performance to a lack of motivation, scientific research shows that the explanation is primarily physiological.

The brain needs a constant supply of oxygen, glucose and water to function efficiently. When the ambient temperature rises, the body begins to prioritise maintaining its thermal balance, diverting some of its resources towards mechanisms such as sweating and increased blood circulation in the skin. This additional effort reduces the energy available for complex cognitive functions, such as sustained attention, working memory and problem-solving (Hancock & Vasmatzidis, 2003).

Attention is one of the first abilities affected by heat

Attention allows us to select relevant information and ignore distracting stimuli. It is essential for activities as varied as driving, studying, working at a computer or taking part in a meeting.

When we are exposed to heat for several hours, this ability begins to decline. Thermal discomfort becomes a constant stimulus competing for the brain's attention. The sensation of heat, sweating, thirst or fatigue uses mental resources that, under normal conditions, would be available for other tasks.

As a result, it becomes more common to:

• lose the thread of a conversation;
• reread the same paragraph several times;
• forget recent information;
• make small errors through inattention;
• take longer to complete tasks.

Although these lapses are generally reversible, they can significantly compromise academic and professional performance.

The impact on memory and decision-making

Another function particularly sensitive to heat is working memory, which is responsible for temporarily keeping information active while we perform a task. This is the ability we use to do mental arithmetic, interpret graphs, plan a presentation or solve a complex problem.

According to Gaoua (2010), an increase in body temperature reduces the efficiency of this function, making logical reasoning more difficult and increasing the time needed to process information.

Decision-making can also be affected. In conditions of intense heat, the brain tends to favour quicker, less considered responses, increasing the likelihood of error. In professions requiring critical decisions — such as those of healthcare professionals, pilots, drivers or industrial workers — this reduction in performance can have important safety implications.

Productivity: a growing challenge

Productivity does not depend solely on motivation or how work is organised. It also depends on the environmental conditions in which tasks are carried out.

International studies show that high temperatures are associated with reduced performance, more errors and the need for more frequent breaks. This impact is particularly evident in outdoor occupations, such as agriculture, construction or infrastructure maintenance, but it also occurs in offices, schools and universities when spaces do not have adequate climate control.

As heatwaves become more frequent, occupational health experts argue that adapting working hours, improving ventilation and creating thermally comfortable environments should be seen not only as well-being measures, but also as strategies to preserve productivity and reduce health risks.

How to protect the brain on hotter days

Although we cannot control the outdoor temperature, there are simple measures that help minimise the effects of heat on the brain.

Hydration is one of the most important. Drinking water regularly, even before feeling thirsty, helps maintain cognitive performance and reduce mental fatigue. Diet also plays an important role. Light meals, rich in fruit and vegetables, help provide water, vitamins and minerals essential for brain function.

Whenever possible, tasks requiring greater concentration should be carried out in the early morning, when the ambient temperature is lower. Taking short breaks throughout the day, seeking out cool places and avoiding prolonged exposure to intense heat are also effective strategies.

Sleep deserves special attention. Sleeping in a cool, well-ventilated bedroom with suitable bedding promotes restorative rest and improves cognitive performance the following day.

Conclusion: protecting the brain means protecting quality of life

For a long time, heat was seen merely as a source of physical discomfort. Today, we know that its effects go far beyond feeling tired or needing to drink more water. The brain is one of the organs most sensitive to high temperatures, responding with changes in attention, memory, mood and the ability to make decisions.

In the context of climate change, with heatwaves becoming increasingly frequent, understanding this relationship is essential to protect health and promote well-being. Small changes in habits — such as staying well hydrated, ensuring good-quality sleep, adjusting the timing of more demanding activities and seeking out cool environments — can make a significant difference.

Caring for our health in summer therefore means looking beyond the skin and recognising that protecting the brain is equally fundamental to preserving quality of life, productivity and emotional balance.

References

• Cian, C., Barraud, P. A., Melin, B., & Raphel, C. (2001). Effects of fluid ingestion on cognitive function after heat stress or exercise-induced dehydration. International Journal of Psychophysiology, 42(3), 243–251.
• Gaoua, N. (2010). Cognitive function in hot environments: a question of methodology. Scandinavian Journal of Medicine & Science in Sports, 20(Suppl. 3), 60–70.
• Hancock, P. A., & Vasmatzidis, I. (2003). Effects of heat stress on cognitive performance: The current state of knowledge. International Journal of Hyperthermia, 19(3), 355–372.
• Intergovernmental Panel on Climate Change (IPCC). (2023). Climate Change 2023: Synthesis Report.
• Obradovich, N., Migliorini, R., Mednick, S. C., & Fowler, J. H. (2018). Nighttime temperature and human sleep loss in a changing climate. Science Advances, 4(5), eaar8592.
• Romanello, M., et al. (2023). The 2023 Report of the Lancet Countdown on Health and Climate Change. The Lancet.
• World Health Organization. (2021). Climate change and health