Summer brings out the worst in people; some days it feels like if the temperature rises one more degree everyone will snap. A seasonal uptick in violent crime may be due to discomfort and irritability, but can the weather actually drive you crazy?
It depends on how hot it is, and whether you're mentally stable to begin with. Intense heat increases the risk of dehydration, and even mild dehydration can affect the brain. A study published this summer tested two dozen college-age men and found that a loss of 1 percent body mass via exercise-induced sweating (replaceable with three glasses of water) decreased their cognitive performance and increased levels of anxiety.
Dramatic overheating can also lead to heatstroke, symptoms of which progress from confusion and irritability to hallucinations, violent behavior, and delirium. In animal models, overheating causes some neurons to become more excitable, which might underlie the psychiatric effects. Most of these are transient—cool off and they go away—but heatstroke may lead to long-term brain damage. (It can also kill you.) You won't keep hallucinating for years to come, but you might end up a little clumsy or slur your speech. Case reports of long-lasting personality changes (similar to those caused by traumatic brain injury) also exist, but this complication appears to be rare.
You may be particularly vulnerable to heatstroke (and thus heat-induced insanity) if you're taking certain psychiatric and neurological medications. Drugs that have anti-cholinergic properties (including some of those used to treat schizophrenia, depression, and Parkinson's disease) inhibit perspiration and otherwise increase the risk of overheating.
Easing into the muggy weather makes heatstroke less likely, which may be why sudden hot snaps have been specifically linked to increased suicide rates. One recent analysis suggested temperature-suicide correlations are tantalizing enough to merit further research, especially in light of global climate change. And a 2008 study of heat waves in Adelaide, South Australia, found that hospital admissions for mental disorders increased at temperatures of 80 degrees or above, with schizophrenics being at especially high risk.
Urban legend—and popular culture—has it that a vacationing psychiatrist can cause some patients to suffer summer mental health episodes. Since many city-dwellers head for cooler climes in August, it's true that therapists are often away during heat waves. However, there is no direct evidence to support the claim that a therapist on vacation is a psychiatric risk factor.
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Explainer thanks Eberhard Deisenhammer of Innsbruck Medical University, Austria.