Extreme heat does not affect only older people or those living with chronic health conditions. Anyone can develop a heat-related illness when the body is exposed to high temperatures for too long, particularly when humidity, strenuous physical activity, dehydration or inadequate access to cooling make it harder to release heat. The Hellenic National Public Health Organization, EODY, stresses that everyone is vulnerable to the health effects of heat, although some groups face a significantly higher risk.

Heat exhaustion and heatstroke may share symptoms such as headache, dizziness, nausea and an elevated body temperature, but they are not equally dangerous. Heat exhaustion is a warning that the body is struggling to cope, often because it has lost too much water and salt through sweating. Heatstroke, by contrast, is a life-threatening medical emergency in which the body can no longer regulate its temperature effectively and brain function may be affected.

Recognising the difference matters because heat exhaustion often improves with prompt cooling and hydration, whereas suspected heatstroke requires an immediate emergency call and rapid cooling while help is on the way.

What happens when the body overheats?

The body normally controls its internal temperature by increasing blood flow to the skin and producing sweat. As sweat evaporates, heat is released into the environment. This cooling mechanism becomes less effective when the temperature is very high, the air is humid, there is little air movement, clothing prevents heat loss or physical exertion generates additional internal heat.

According to the World Health Organization, prolonged exposure to high daytime and nighttime temperatures places cumulative stress on the body. The effort required to remain cool can also strain the heart and kidneys, worsen existing diseases and increase the risk of acute kidney injury.

Heat exhaustion generally develops when fluid and salt losses, combined with ongoing heat exposure, begin to overwhelm the body’s ability to compensate. If exposure continues or cooling is delayed, the condition may progress to heatstroke, although heatstroke can also appear suddenly, particularly during intense exercise or physical work.

The main differences at a glance

Sign


Heat exhaustion


Heatstroke

Mental state


Usually alert, although tired, dizzy or irritable


Confusion, unusual behaviour, poor coordination, slurred speech, seizure or loss of consciousness

Sweating and skin


Often heavy sweating with cool, pale or clammy skin


Skin may be hot, dry or still sweating heavily

Pulse


Often fast and weak


Usually fast and strong

Temperature


Elevated


Very high, often around or above 40°C, but action should not wait for a measurement

Main response


Stop activity, cool the person and provide small sips of fluid if fully alert


Call emergency services immediately and begin rapid cooling

Fluids by mouth


Appropriate in small, frequent amounts if the person is conscious and can swallow


Do not give anything to drink when heatstroke is suspected

The most important dividing line is not whether the person is sweating. It is the appearance of neurological symptoms such as confusion, disorientation, abnormal behaviour, difficulty speaking, loss of coordination, seizure or reduced consciousness. The CDC notes that people with heatstroke may have either hot, dry skin or profuse sweating, especially when the condition is caused by strenuous physical activity.

What are the symptoms of heat exhaustion?

Heat exhaustion is the body’s response to excessive loss of water and salt, usually through heavy sweating. It may develop after prolonged exposure to high temperatures or appear more quickly during exercise, outdoor work or activity in a hot, humid environment.

Possible symptoms include:

- heavy sweating,


- cool, pale or clammy skin,


- intense thirst,


- tiredness, weakness or irritability,


- headache,


- dizziness or feeling faint,


- nausea or vomiting,


- muscle cramps,


- a fast, weak pulse,


- an elevated body temperature,


- reduced urine output,


- fainting.

Not every person will experience every symptom. Children may become unusually irritable, while older adults may initially appear weak, unsteady, withdrawn or less responsive than usual.

What should we do for heat exhaustion?

The person must stop all physical activity and be moved immediately to a shaded, cool or air-conditioned place. Unnecessary clothing, shoes and socks should be removed or loosened so that heat can escape more easily.

Cooling should begin without delay. The skin can be sprayed or sponged with cool water while air is circulated with a fan. Cool, wet cloths may be placed on the body, particularly around the neck and under the arms, or the person may take a cool shower or bath.

If the person is fully conscious, able to swallow and not vomiting, offer small, frequent sips of cool water. An oral rehydration or isotonic drink may also be used after prolonged heavy sweating. People who have been advised to restrict fluids or sodium because of heart, kidney or another medical condition should follow their clinician’s instructions.

Someone should remain with the affected person and observe whether their condition is improving. The NHS advises that the person should begin to cool down and feel better within approximately 30 minutes. EODY recommends immediate medical help if vomiting occurs, symptoms worsen or continue for more than one hour. A lack of clear improvement after initial cooling should therefore prompt urgent medical assessment, particularly in a child, an older adult or someone with a chronic illness.

Confusion, loss of coordination, a seizure, loss of consciousness or a rapidly worsening condition should no longer be treated as simple heat exhaustion. These signs indicate possible heatstroke and require an immediate emergency call.

What are the warning signs of heatstroke?

Heatstroke occurs when the body is no longer able to control its temperature adequately. Body temperature can rise rapidly, and injury to the brain, kidneys, liver, heart and muscles may follow. Delayed treatment can result in permanent disability or death.

Warning signs include:

- confusion, disorientation or unusual behaviour,


- agitation or extreme restlessness,


- difficulty speaking or slurred speech,


- poor balance or lack of coordination,


- seizure,


- fainting or loss of consciousness,


- a very high body temperature,


- hot or flushed skin, which may be dry or sweaty,


- rapid breathing,


- a fast, strong pulse,


- severe headache, dizziness, nausea or vomiting.

A temperature of around 40°C or higher strongly supports suspicion of heatstroke, but it is not necessary to obtain a thermometer reading before taking action. A person exposed to heat who develops confusion or another change in mental status should be treated as a medical emergency.

What should we do if heatstroke is suspected?

Call emergency services immediately. In Greece, call 112 or EKAB at 166, both recognised official emergency numbers by the Greek government. Do not wait to see whether the person will recover spontaneously and do not leave them alone.

While waiting for help:

- Move the person to a shaded, cool or air-conditioned place and remove unnecessary outer clothing.


- Begin cooling immediately. Wet the skin or clothing with cool water and fan continuously.


- Place wrapped cold packs or cool, wet cloths around the neck, under the arms and near the groin.


- If it can be done safely, cooling in cold water can be used, especially after exertional heatstroke.


- Do not give the person anything to drink, as advised by EODY.


- If the person becomes unconscious but continues to breathe, place them in the recovery position. If they are not breathing normally, follow the emergency dispatcher’s instructions and begin CPR if able.

The emergency call and cooling must happen at the same time whenever another person is available to help. Cooling should not be postponed until the ambulance arrives.

Can a person with heatstroke still be sweating?

Yes. The belief that heatstroke always causes hot, completely dry skin is dangerous. Classic heatstroke, which often develops gradually in older or chronically ill people during a heatwave, may be associated with reduced sweating. Exertional heatstroke, which can affect athletes, workers and otherwise healthy adults, frequently occurs while the person is still sweating heavily.

Skin moisture alone therefore cannot distinguish heat exhaustion from heatstroke. Mental status and neurological function are more important warning signs.

Who is at greater risk?

Although extreme heat can affect anyone, EODY identifies several groups that require greater protection:

- infants, children and older adults,


- pregnant or breastfeeding women,


- people with cardiovascular disease, hypertension, diabetes, respiratory disease, kidney or liver disease,


- people living with dementia, serious neurological conditions or mental illness,


- people taking medicines that affect fluid balance, sweating, blood pressure or temperature regulation,


- people who are overweight or obese,


- outdoor and manual workers,


- athletes and people exercising intensely,


- people consuming large amounts of alcohol or using drugs,


- people with fever, vomiting, diarrhoea or another acute illness,


- people living alone or without access to a cool environment.

Medicines should never be stopped or adjusted without medical advice. People taking diuretics, blood-pressure medication, antidepressants, antipsychotics, antihistamines, anticholinergic medicines or diabetes medication may need individual guidance during periods of extreme heat.

Being young or physically fit does not provide complete protection. Intense exertion can generate heat faster than the body can release it, particularly when the person is not acclimatised to the environment.

How can heat-related illness be prevented?

During periods of extreme heat, outdoor activity and strenuous exercise should be scheduled for the cooler parts of the day. Light, loose-fitting clothing, regular hydration and frequent breaks in shaded or air-conditioned places can reduce thermal strain. Alcohol should be limited because it can contribute to dehydration and impair judgement.

Homes should be kept shaded during the hottest hours, with windows opened at night when outdoor air is cooler. A fan may improve comfort, but during extreme temperatures it is not a substitute for an air-conditioned room, cool shower or another effective method of reducing body heat.

Older people and others at increased risk should not remain isolated during a heatwave. Regular contact is essential, particularly if they live alone, have limited mobility or do not have access to air conditioning. Babies, children, dependent adults and animals must never be left inside a parked vehicle, even with the windows partly open.

The warning sign we should never ignore

Headache, dizziness and heavy sweating can occur in heat exhaustion, but a change in mental state changes the level of urgency. Confusion, unusual behaviour, difficulty speaking, loss of coordination, seizure or reduced consciousness after heat exposure should be treated as possible heatstroke.

The safest rule is simple: move the person out of the heat, begin cooling and call emergency services immediately. With heatstroke, every minute without effective cooling increases the risk of organ damage.

Sources and further reading

- EODY: Heatwave guidance


- EODY: Heatstroke and heat exhaustion


- CDC/NIOSH: Heat-related illnesses


- World Health Organization: Heat and health


- NHS: Heat exhaustion and heatstroke


- Greek government: National emergency numbers https://healthpont.com/?p=41276