Parts of the UK are bracing for a weekend of sizzling heat following days of record-breaking temperatures across the country.Kew Gardens in London reached 35.1C on Monday, exceeding its previous station record of 29.3C and the previous UK May record of 32.8C.The Met Office said that 163 stations broke their May maximum temperature records in total.Saturday will continue to deliver sunshine, as temperatures are set to climb as high as 29C in England and Wales.While intense heat can cause physical discomfort and exhaustion, it can also affect our mental wellbeing and overall mood.Dr Ravi Gill, a health psychologist, has shared why prolonged high temperatures can cause anger and anxiety – and her top tips for maintaining balance.Heat can impair sleep and raise stress hormones (PA Archive)How does hot weather impact our mood?Physiological changes in the body and brain due to heat can significantly affect mood during a heatwave. “Heat disrupts neurotransmitter systems (serotonin), impairs sleep and raises stress hormones like cortisol, which are key regulators of mood and impulse control,” says Dr Gill.The physical discomfort and disrupted sleep from heatwaves can also exacerbate mood instability, trigger anxiety spikes, or worsen irritability, says the psychologist.“Lingering discomfort and environmental stress strains emotional resilience, making even minor irritants feel overwhelming,” adds Dr Gill. “Heatwaves can also escalate social tensions – whether at home, in traffic, or public spaces – turning minor triggers into conflicts.”Research also suggests that people with pre-existing mental health conditions are more vulnerable during heatwaves.“Conditions such as anxiety, depression, bipolar disorder, or schizophrenia can make it harder to recognise early signs of heat stress or to take action.“In addition, some psychiatric medications (e.g., antipsychotics, certain antidepressants, mood stabilisers) reduce the body’s ability to sweat or regulate temperature, increasing the risk of heat exhaustion or heatstroke.”Nighttime heat makes it harder for the body to drop its core temperature (Alamy/PA)What impact do sleep disturbances by heat have on our mood and minds?“High nighttime temperatures make it harder for the body to drop its core temperature, which is essential for initiating and maintaining deep, restorative sleep,” says Dr Gill. “People wake more often, particularly during REM sleep, which is vital for emotional processing and memory consolidation. Difficulty falling asleep and staying asleep reduces overall rest.”This can have a profound impact on our emotional regulation.“Poor sleep lowers activity in the prefrontal cortex (responsible for impulse control) and heightens amygdala reactivity (linked to fear, anger, and anxiety). This makes us more emotionally volatile,” explains Dr Gill. “Lack of REM sleep amplifies stress responses and reduces resilience to everyday frustrations.“In addition, sleep deprivation impairs attention, working memory, decision-making, and problem-solving, increasing mental fatigue.”Heatwaves can impact and impair core cognitive functions like memory. (Alamy/PA)What impact can heatwaves have on our brains?“Heatwaves can impact and impair core cognitive functions like memory, focus and decision-making, and the reasons are a mix of direct brain effects and secondary factors like dehydration and sleep disruption,” says Dr Gill.Reduced cerebral blood flow, neurotransmitter disruption and electrolyte imbalance are just a few factors that can have significant impacts on our cognitive function during a heatwave.“High temperatures can cause blood vessels to dilate and divert blood toward the skin for cooling, reducing blood flow and oxygen delivery to the brain’s thinking centres (especially the prefrontal cortex),” explains Dr Gill.“Meanwhile, heat stress also alters the balance of dopamine, serotonin and acetylcholine, which are critical for attention, learning and memory.“Sweating also depletes sodium, potassium, and other electrolytes, affecting nerve signal transmission and slowing mental processing.”What impact can dehydration have on our mood?“Even mild dehydration (1-2 percent body weight loss in fluids) can slow neural processing and impair memory, attention, and reaction time,” says Dr Gill. “Dehydration increases cortisol and alters serotonin activity, leading to irritability, anxiety, and lower frustration-tolerance.“Reduced blood volume and electrolyte imbalances limit oxygen and nutrient delivery to the brain, causing mental sluggishness.”Here are some coping strategies to help counter-balance some of these effects.Drink water regularly, not just when you feel thirsty (Alamy/PA)Prioritise hydration with electrolytes“Drink water regularly, not just when you feel thirsty, and include electrolyte sources,” advises Dr Gill. “This helps to maintain optimal brain signalling, prevents cognitive slowing, and reduces irritability linked to dehydration.”Maintain a cooling sleep environment “Try to keep to a consistent sleep-wake schedule. Use fans, blackout curtains, breathable bedding, and, if possible, pre-cool your bedroom before sleep,” recommends Dr Gill. “Preserving deep and REM sleep protects emotional regulation, memory consolidation, and decision-making capacity.”Practise heat-adapted stress regulation “Use grounding or breathing exercises in cooler parts of the day – gentle stretching or yoga in shaded or air-conditioned spaces can also help,” says Dr Gill. “These regulate cortisol and keep the nervous system from staying in a prolonged ‘fight-or-flight’ state.”Structure your day around the heat“Schedule mentally demanding tasks for cooler morning hours and take regular breaks during peak heat,” suggests Dr Gill. “This protects focus and working memory, reducing mistakes caused by heat-related cognitive fatigue.”