Research suggests that extreme heat worsens human mental health and cognitive function, and increases aggressive behavior.

Extreme heat is known to negatively impact people's health by causing dehydration, heatstroke, and summer fatigue. However, research has shown that the negative effects of extreme heat are not limited to the physical; it can also worsen mental health and cognitive function, and increase aggressive behavior and self-harm.

Heat on the brain: The impacts of rising temperatures on psychiatric functioning, potential causes, and related compounding factors.
https://psycnet.apa.org/record/2025-56035-001

Extreme heat takes a severe toll on mental health
https://www.psypost.org/extreme-heat-takes-a-severe-toll-on-mental-health/

While discussions on climate change often focus on the health risks of heatwaves, such as increased risk of heatstroke and cardiovascular disease, the impact of heatwaves on mental health and cognitive function is often overlooked. Therefore, Joseph Tarierzo, a clinical psychologist at New York-Presbyterian Brooklyn Methodist Hospital, has integrated various studies to summarize the relationship between heatwaves and mental health and cognitive function.

Talierzo stated, 'I have long been interested in integrative medicine that connects physical and mental health. As climate change, such as natural disasters, becomes more pronounced, the question naturally arises of how the environment affects our health.'

This review paper, which comprehensively evaluated previous research findings, showed that exposure to extreme heat significantly reduces mood and emotional stability in humans. Even in people without a diagnosed mental illness, temperatures above 20°C were associated with decreased positive emotions and increased fatigue. Furthermore, prolonged exposure to hot weather was associated with an increased incidence of depression and anxiety disorders in the general population.

Talierzo noted that these widespread effects were unexpected. 'I was surprised by the magnitude of the impact that extreme heat has on mental health. I never imagined that even people without pre-existing conditions could be affected,' he said.

Social media activity can sometimes reflect these emotional turmoil. It's said that depressing expressions in social media posts increase significantly on extremely hot days, and these negative posts can spread online, potentially indirectly impacting the mental health of people in cool indoor environments. Studies have also reported that extreme temperatures increase hate speech online.

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For people with pre-existing mental illnesses, the risks of extreme heat are more serious, and rising temperatures and humidity have been closely linked to an increase in hospitalizations for patients with bipolar disorder. Extreme heat and strong sunlight disrupt regular sleep cycles and tend to trigger manic episodes in people with bipolar disorder.

Furthermore, Tallierzo reports that the risk of premature death from extreme heat is higher for people with conditions such as schizophrenia than for people with serious physical illnesses. People with severe mental illness may be homeless or live in environments without air conditioning, and these social factors may further increase their risk of death.

Heat is also linked to aggressive behavior and violence, and studies have reported that rising temperatures increase crime rates, domestic violence, and shooting incidents. Talierzo believes that prolonged exposure to heat may reduce mental resources, making it more difficult to control aggressive impulses.

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Problem behaviors that increase with extreme heat are not limited to external factors; self-harm and suicide may also increase. Suicide rates and emergency room visits due to self-harm have been reported to increase significantly during periods of high temperatures.

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It is known that heat negatively affects basic cognitive functions, and people exposed to high-temperature environments exhibit problems such as decreased reaction time, increased impulsivity, and worsening working memory.

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The proposed biological mechanisms causing these problems include: 'Extreme heat drastically increases the energy required for thermoregulation, putting an overload on the minds and bodies of people who already have mental illnesses'; 'Exposure to heat disrupts the production of neurotransmitters in the brain, negatively affecting mood and stress regulation'; and ' Heat shock proteins that mitigate heat stress in cells cease to function properly, disrupting major hormonal systems.'

Dehydration and sleep deprivation due to extreme heat also play a significant role. Dehydration slows blood flow and inhibits the function of brain enzymes, leading to confusion and fatigue. Furthermore, lack of sleep on hot nights worsens brain inflammation and further weakens emotional and mental defense mechanisms.

Talierzo also points out that the risk of extreme heat is particularly high in urban areas where concrete and asphalt absorb heat, creating a heat island effect , and in historically underserved areas with few trees and green spaces. In addition, he warns that psychotropic drugs used to treat anxiety and depression can inhibit bodily functions such as sweating and blood flow regulation, making mental health patients taking these medications more likely to be hospitalized for heatstroke.

Talierzo said, 'I remain interested in ecological psychology and am actively working to deepen my understanding of various aspects of climate change, such as the effects of pollution and the role of green spaces. Climate change is a health crisis, and none of us are immune to its effects.'