What the heat does to your mental health

As the UK experiences record-breaking temperatures this week, much of the conversation focuses on sunburn, dehydration, and staying cool. But for millions of people particularly those living with a mental health condition, the heat carries a far less visible set of risks. Here's what the clinical evidence actually shows.

We tend to think of extreme heat as a physical problem; Keep hydrated, stay in the shade, wear sunscreen. But the relationship between high temperatures and mental health is something far fewer people understand and for the 16% of the UK population living with a mental health condition, the affect can be significant.

Research published by Oxford University's Department of Psychiatry confirms heatwaves are associated with measurable increases in anxiety, sleep disruption, cognitive decline, mood instability, and hospital admissions for mental health crises. Suicide rates also increase during sustained hot periods.

This is not a niche concern. Over 10 million people in the UK take psychiatric medication daily. Heat affects how those medications work. And even people with no diagnosed mental health condition are not immune to what extreme temperatures do to the brain.

5 Things Extreme Heat Does to Your Mental Health

1

It disrupts sleep — and that disrupts everything else

Sleep is one of the most critical factors in mental health regulation. When night-time temperatures stay high, the body struggles to cool down enough to reach deep, restorative sleep. Research consistently links sleep deprivation to increased anxiety, low mood, irritability, and impaired decision-making. During a heatwave, even one or two nights of poor sleep can meaningfully affect how you feel and function. For those managing anxiety or depression, that disruption can quickly snowball.

2

It amplifies irritability, anxiety, and stress — even in healthy people

Oxford researchers note that heat causes increased levels of irritability, anxiety, and stress even in people without a mental health diagnosis. We've all experienced it; the disproportionate reaction to a small frustration when we're overheated. That's not weakness: it's your nervous system responding to physiological stress. Studies show that aggression, conflict, and stress responses all increase measurably in hot conditions. Understanding this can reduce shame and help people extend themselves (and others) a little more patience.

3

It affects how psychiatric medications work

This is the one most people don't know about. Many commonly prescribed psychiatric medications — including SSRIs, antidepressants, antipsychotics, and mood stabilisers — interact with heat in ways that can be problematic.

SSRIs in particular can increase sensitivity to heat, raising the risk of heat exhaustion and heat stroke. Some medications reduce the body's ability to sweat and regulate temperature. Others affect how the kidneys process fluids. If you or someone you care for is on psychiatric medication, keeping cool and staying hydrated during a heatwave isn't optional advice; it's clinically important.

4

It can trigger or worsen existing mental health conditions

For people living with bipolar disorder, extreme heat has been identified as a potential trigger for switching into a manic or hypomanic phase. For those with depression, the combination of disrupted sleep, isolation (staying indoors to avoid heat), and physical discomfort can deepen a low mood episode. For those with anxiety, the physical sensations of heat (racing heart, shallow breathing, dizziness) can be misread as panic symptoms, triggering a cycle of heightened anxiety. A&E admissions for mental health reasons increase by around 10% during sustained hot periods.

5

It reduces our capacity to think clearly

Heat impairs cognitive function; processing speed, attention, memory, and concentration all decline in high temperatures. Research from Harvard found that students in non-air-conditioned rooms during a heatwave performed measurably worse on cognitive tests than those in cooled environments. For people who are already managing cognitive load due to stress, trauma, or mental health difficulties, the additional cognitive drain of extreme heat can feel overwhelming. This is not a character flaw. It is a physiological response.

10%

Increase in mental health-related A&E admissions during periods of sustained extreme heat (Oxford University, 2026)

"Far fewer people are aware of the mental health impacts of extreme heat. For the 16% of the UK population living with a mental health condition, heat can pose a range of challenges — some of which can be quite serious."

Dr Laurence Wainwright, Senior Researcher in Psychiatry, University of Oxford

Who Is Most at Risk?

Certain groups face greater vulnerability during heatwaves:

People on psychiatric medication; particularly SSRIs, antipsychotics, and lithium, which all interact with heat regulation in different ways.

People living with bipolar disorder, schizophrenia, or severe depression, where heat can trigger phase changes or deepen existing symptoms.

People who are socially isolated, those without air conditioning or access to cool spaces, who may also have less social support to notice when they're struggling.

Children and young people, whose developing nervous systems are more sensitive to both temperature extremes and disrupted sleep.

Older adults, who may have reduced awareness of thirst and body temperature changes, compounding both physical and psychological risks.

What You Can Actually Do - Practical Steps for This Week

Hydrate proactively, not reactively. By the time you feel thirsty in extreme heat, you're already mildly dehydrated. Dehydration directly impairs mood and cognitive function. Aim for small amounts frequently rather than large amounts occasionally.

Prioritise sleep conditions above everything else. Use a fan directed at a bowl of ice, keep curtains closed during the day to reduce room temperature overnight, and consider a cool (not cold) shower before bed. Poor sleep is the biggest amplifier of heat-related mental health effects.

If you're on psychiatric medication, speak to your GP or prescriber. Ask specifically about heat interactions for your medication. Don't adjust doses independently, but do ask the question. Your pharmacist is also a good first port of call.

Reduce stimulation in the evening. Heat plus screens plus news equals an overstimulated nervous system at bedtime. Protect the two hours before sleep; cool, dark, quiet, calm.

Check in on people who live alone. Social isolation during a heatwave is a genuine risk factor. A five-minute call to check in can make a real difference; particularly for older adults, those with mental health conditions, and anyone you know is struggling.

Name what's happening. If you find yourself unusually irritable, anxious, low, or foggy this week; consider that the heat may be a significant factor. That awareness alone can reduce shame and help you respond more compassionately to yourself.

Frequently asked questions about heat and mental health

1. Does hot weather affect mental health? Yes, and more significantly than most people realise. Research from Oxford University's Department of Psychiatry confirms that extreme heat is associated with increased anxiety, irritability, sleep disruption, and a measurable rise in mental health-related A&E admissions. Even people without a diagnosed mental health condition experience cognitive decline and mood changes during sustained hot periods.

2. Can heat affect how antidepressants work? Yes. SSRIs and other antidepressants can increase the body's sensitivity to heat, raising the risk of heat exhaustion and heat stroke. Some psychiatric medications also affect the body's ability to sweat and regulate temperature. If you are on any psychiatric medication, speak to your GP or pharmacist about staying safe during a heatwave.

3. Why does heat make anxiety worse? Extreme heat produces physical sensations, such as a racing heart, shallow breathing, dizziness etc; that closely mirror anxiety and panic symptoms. For someone already managing anxiety, these can trigger a heightened fear cycle. Heat-induced sleep deprivation compounds this further.

4. How does a heatwave affect sleep and mental health? When high overnight temperatures prevent deep sleep, the effects accumulate: increased anxiety, low mood, poor concentration, and emotional dysregulation. Prioritising sleep conditions during a heatwave is one of the most effective mental health interventions available.

5. Who is most at risk of mental health problems during a heatwave? People on psychiatric medication, those with bipolar disorder, depression, anxiety or schizophrenia, socially isolated individuals, children, and older adults all face heightened risk.

6. Is it normal to feel low or irritable in hot weather? Completely. These are normal physiological responses not weakness. Research shows they occur even in people with no history of mental health difficulties.