A doctor has revealed that the strangest – and one of the most dangerous – symptoms of heatstroke that most people don’t know about, ahead of reports that another heatwave will hit the UK in early August.

Dr Alexander Joshue Acosta Peñafiel – a medical doctor with experience in primary care and emergency medicine – says that one of the biggest warning signs of heatstroke is personality changes.

‘I’ve worked long enough in the emergency unit to know that heatstroke rarely comes up in the manner I expect it to manifest,’ Dr Alexander says, who trained in Ecuador, where temperatures and humidity remain high year-round.

‘The cases that stayed with me weren’t the ones with flushed skin and high temperature readings.

‘They were the ones where a family member notified me and said, ‘he’s just not acting like himself’.’

Behaviour and personality changes indicate a serious level of heatstroke that needs to be dealt with immediately.

‘The frontal lobe of the brain is the place where personality and impulse control reside, and it’s one of the first areas of the brain to fight back when the centre of the brain gets too hot,’ he said.

‘That is why out-of-character behaviour or aggression is often present before slurred speech or loss of balance occurs.’

Dr Alexander, who currently works as a GP in Ecuador, says that when patients present this symptom, it should be treated as a medical emergency.

Discussing one particular patient, he said: ‘By the time I got to examine the patient, his core temperature was far exceeding the limits of what I could work with.

‘That change in behaviour was a warning sign, and almost no one around him had realized that this was a medical emergency.’

The doctor explains that the body temperature will likely continue to rise every minute after that behavioural change, until it reaches exhaustion.

‘Once the central nervous system begins to be affected at 104°F [40 degrees Celsius], the greater the duration of hyperthermia above that temperature, the greater the likelihood of permanent neurological damage.

‘During my emergency rotations, if a patient came in with a sudden change in mental status who came from a hot environment, we treated the change in mental status as a neurological emergency until proven otherwise.’

‘The danger lies in most people not making the link between the behaviour change and temperature.

‘Patients would come into the ER who had been sitting in the heat an additional 20 to 30 minutes because the individuals around them thought rest and water was sufficient.

‘Some recovered fully. The distinction between those two outcomes was almost always dependent on the speed at which they recognize the behaviour as a symptom rather than a mood.’

The doctor hopes to increase awareness of this lesser-known but dangerous symptom.

If behaviour changes are observed during a heatwave, he says: ‘Call emergency services right away before doing anything else.

‘Once help is on the way, get the person out of the heat and place ice or cold cloths on the neck and armpits, where major blood vessels are closer to the surface of the skin.’

‘Do not give the person fluids by mouth if they seem confused or cannot follow simple instructions. That is because aspiration is a real risk at that point.

‘The instinct is to keep them hydrated, but do not give the person anything through the mouth since they cannot safely swallow.

‘The two things that can make a difference in the first few minutes are rapid cooling and the involvement of emergency services.’