What hot weather does to your brain, and why you feel so irritated

Temperatures are soaring, and many will be feeling restless, irritable and discontent.

Thursday saw the hottest start to May on record, with temperatures reaching 28C in London's Kew Gardens.

“The previous May 1st record high temperature was 27.4C at Lossiemouth in Scotland in 1990,” the Met Office said in a post on X.

The mercury was “still climbing”, the post said.

Hot weather can have a number of impacts on brain function, Dr Steven Allder, a consultant neurologist at Re:Cognition Health, says – affecting everything from memory and concentration to emotional stability.

“Heat can impair several areas of cognitive performance, including attention, short-term memory and decision-making,” Dr Allder says.

“When the body overheats, resources are diverted from the brain to regulate core temperature, which can slow processing speed and reduce mental clarity.

“People may find it harder to concentrate, solve problems or retain information. This is especially noticeable during prolonged heat exposure or dehydration, which further affects neural efficiency.”

Can hotter temperatures impact emotional instability?

“There is growing evidence linking hotter temperatures to emotional instability,” says Dr Allder.

“Elevated heat levels have been associated with increased irritability, frustration and even aggression.

“This may be due to disrupted sleep, discomfort, or heightened stress responses. The brain’s emotional regulation centres, particularly the amygdala, may become more reactive in extreme heat.”

Can heat contribute to mental fatigue?

Hot weather can significantly contribute to mental fatigue.

“When the body is trying to cool itself, more energy is used for thermoregulation, leaving fewer resources available for cognitive functioning,” explains Dr Allder.

“This can result in feelings of tiredness, mental sluggishness and reduced alertness. Tasks that require concentration or decision-making become more difficult and motivation may drop.

“Mental fatigue during heat exposure is particularly common when hydration is inadequate or when individuals are exposed to prolonged periods of warmth without adequate rest or cooling.”

Are there any positive health impacts of hot weather?

Warm weather can have positive effects on the brain, particularly through increased exposure to sunlight.

“Sunlight stimulates the production of serotonin, which helps improve mood, sleep, and overall emotional balance,” says Dr Allder.

“Higher vitamin D levels, often resulting from sun exposure, are also linked to improved cognitive function and mental health.

“People tend to be more active and socially engaged during warm weather, which benefits brain health. However, these advantages are most apparent when temperatures remain comfortable and not excessively hot.”

Are people with neurological conditions more vulnerable to heat-related changes?

People with neurological conditions such as multiple sclerosis (MS), epilepsy and migraines are more susceptible to heat-related symptoms.

“In MS, even small increases in temperature can worsen fatigue and impair nerve conduction,” notes Dr Allder.

“For those with epilepsy, heat and dehydration may lower seizure thresholds. Migraines can be triggered or intensified by high temperatures and changes in atmospheric pressure.

“These individuals need to take particular care in hot weather, as their conditions make it harder for the nervous system to tolerate thermal stress.”

What long-term neurological effects might be associated with chronic exposure to high temperatures?

“Prolonged heat stress can contribute to systemic inflammation, oxidative stress and vascular dysfunction, all of which can negatively affect the brain,” says Dr Allder.

“Over time, this could increase the risk of cognitive decline, poor sleep, and potentially neurodegenerative diseases.

“Repeated dehydration episodes may also impair brain structure and function.”

Are there any adaptive mechanisms the brain uses over time to cope with frequent heat exposure?

“The brain and body can gradually adapt to frequent heat exposure through a process known as heat acclimatisation,” explains Dr Allder.

“Over time, the body becomes more efficient at regulating temperature by improving sweat response, blood flow and cardiovascular efficiency.

“While these changes help protect the brain from overheating, they may not fully prevent cognitive or emotional strain.

“The degree of adaptation varies between individuals and depends on factors such as age, fitness, and underlying health conditions.”

 Is there anything we can do to protect our brain health in hot weather?

“Staying well-hydrated is essential, as even mild dehydration can impair cognitive function,” says Dr Allder.

“Limiting time outdoors during peak heat hours, wearing light clothing and using fans or air conditioning can help maintain a safe body temperature.

“Eating light meals, taking regular rest breaks and ensuring good sleep hygiene are also beneficial. Those with neurological conditions should also take extra precautions and may benefit from personalised advice from their healthcare providers.”