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Extreme heat affects not only physical health but also mental balance, according to Prof. Dr. Hulya Ensari, a faculty member in the Department of Mental Health and Diseases at Atlas University in Istanbul, Türkiye's largest city.
In a statement released by the university, Ensari said rising temperatures and humidity can weaken anger control, disrupt sleep quality and increase the risk of flare-ups in depression, bipolar disorder and psychotic disorders.
She added that people taking psychiatric medication should pay closer attention to fluid and electrolyte balance, as well as drug side effects, during hot weather.
Ensari said increased arguments, shorter tempers in traffic and sudden outbursts during heat waves cannot be explained by psychological fatigue alone, since heat regulation and the regulation of emotion and sleep rely on shared mechanisms in the brain. "The impact of heat on mental state is not indirect; it is direct," she said.
She explained that when fluid and electrolyte loss, heightened alertness and disrupted sleep occur together, the brain's prefrontal functions, which are responsible for impulse control, weaken, while threat assessment becomes more dominant.
Ensari linked anger outbursts to this neurobiological imbalance, noting that the relationship between heat and aggression has been demonstrated repeatedly across different countries, periods and research methods.
She said humidity worsens the effect by blocking sweat evaporation, the body's main cooling mechanism, keeping alertness levels elevated.
Ensari also warned that hot weather can pose additional risks for people using antipsychotic, anticholinergic, antidepressant and stimulant medications, due to their effects on the body's temperature regulation and potential side effects.
She said the impact of extreme heat on mental state varies between individuals and that no single temperature is a critical threshold for everyone.
"There is no sharp threshold that applies to everyone," she said, adding that risk rises gradually with temperature rather than at a fixed point. Ensari said personal risk depends on factors including age, cardiovascular or neurological conditions, medication use, alcohol consumption, heat adaptation and humidity levels.
Sleep, she said, is a key mechanism linking heat to mental health, since falling asleep depends physiologically on heat loss through dilation of blood vessels near the skin, which lowers core body temperature.
When ambient temperature remains high, this process is disrupted, lengthening the time it takes to fall asleep and increasing nighttime waking.
Ensari noted that insomnia is one of the risk factors that can trigger bipolar disorder and manic episodes, and said hospital admissions related to these conditions peak during summer months, a pattern she said has been linked to high temperatures in scientific studies.
To help protect mental and physical health during hot weather, Ensari recommended keeping bedrooms cool and ventilated, or airing them out for one to two hours before sleep if cooling is not possible.
She advised taking a warm shower before bed to help lower core temperature, avoiding alcohol in the evening, spreading fluid intake throughout the day and avoiding outdoor exposure between 11:00 and 16:00.
She also urged people to monitor the fluid intake and mental state of relatives on psychiatric medication, noting that confusion, speech difficulty or a sudden stop in sweating should prompt emergency medical attention. Ensari advised against discontinuing psychiatric medication without medical guidance, saying dosage and timing should be discussed with a physician.
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