Heat exhaustion and heat stroke

What this article covers

What is the difference between heat exhaustion and heat stroke?
Who is most at risk?
How do you recognise heat stroke?
First aid: how to cool someone rapidly
Prevention: protecting yourself in extreme heat
Protecting children and older adults
What happens in hospital after heat stroke?
When to call emergency services without delay

What is the difference between heat exhaustion and heat stroke?

Both conditions arise from the body overheating, but they differ fundamentally in severity and what needs to happen next. Heat exhaustion occurs when the body loses more fluid and salt than it replaces, leaving the person feeling weak, dizzy, nauseous and headachy. Their thinking is clear and they know where they are.

Heat stroke means the body has lost its ability to regulate its core temperature. Internal temperature climbs above 40 degrees Celsius and organs begin to sustain damage. The defining feature that separates it from heat exhaustion is a change in mental state: confusion, irrational behaviour, aggression without cause, loss of coordination, or loss of consciousness.

The most common mistake is waiting to see how symptoms develop before acting. The safe approach is to treat any person who shows confusion or altered behaviour in a hot environment as a heat stroke case until proven otherwise. The cost of treating heat exhaustion as aggressively as heat stroke is low. The cost of treating heat stroke as heat exhaustion can be permanent organ damage or death.

Heat exhaustion versus heat stroke

Feature	Heat exhaustion	Heat stroke
Core temperature	Elevated but usually below 40 C	Above 40 degrees Celsius
Mental state	Normal, person is alert	Confused, irrational or unconscious
Skin	Pale, wet, sweating	May be dry and hot or wet
Severity	Serious, needs intervention	Life-threatening emergency
First action	Rest, cool, rehydrate	Emergency services and immediate cooling

Who is most at risk?

A 2022 review published in BMJ Medicine identified the main risk factors for exertional heat stroke. Outdoor workers in extreme heat are at the top, particularly in construction, agriculture and sanitation roles in the Gulf states where ambient temperatures regularly exceed 45 degrees Celsius and high humidity reduces the body's ability to cool itself through sweating. Athletes and pilgrims undertaking intense physical activity in heat also face high risk.

Older adults are more vulnerable because their ability to detect rising body temperature and produce adequate sweat diminishes with age. Children under four years lose water at a higher rate relative to their body size and do not reliably complain about heat before it becomes dangerous. People taking certain medications, including diuretics, anticholinergic drugs and some blood pressure medicines, lose the physiological capacity to adapt to heat.

Diabetes, heart disease, severe obesity and alcohol use all increase risk independently. Someone who has recently moved from a cooler climate to a hot one and has not had time to acclimatise is significantly more vulnerable than someone whose body has adjusted gradually. Acclimatisation takes 10 to 14 days and produces genuine physiological changes that reduce heat strain: increased plasma volume, earlier onset of sweating and more efficient distribution of blood to the skin.

One of the most underappreciated risk situations in the region is being left in or near a parked car. Vehicle interiors reach lethal temperatures within ten to fifteen minutes on a sunny day even when the outside temperature seems moderate, and children who cannot exit themselves are particularly at risk. This scenario is entirely preventable with awareness.

How do you recognise heat stroke?

The central sign that distinguishes heat stroke from lesser heat illness is a change in mental state. The person may appear confused, speak incoherently, show uncharacteristic aggression, lose balance when walking or become unresponsive. These mental signs are the most important warning flag and should trigger an emergency call immediately.

A very high core body temperature, usually above 40 degrees Celsius, is necessary for the diagnosis. But in a field setting, do not delay treatment while searching for a thermometer. If a person is confused in a hot environment after prolonged exertion or sun exposure, treat it as heat stroke.

Other accompanying signs include cessation of sweating or profuse sweating, flushed and hot skin, nausea and vomiting, a rapid and weak pulse, and in severe cases seizures. Do not wait for all of these to be present. Begin cooling and call emergency services at the same time.

First aid: how to cool someone rapidly

The most important intervention in heat stroke is rapid cooling. The research is clear that every minute of delay in cooling increases organ damage. A 2017 review in Current Sports Medicine Reports confirmed that immersion in cold water is the fastest and most effective method of lowering core body temperature in heat stroke.

In practical settings, do not wait for an ambulance to start cooling. Move the person immediately to shade or an air-conditioned space. Remove excess clothing. Apply ice packs or cold wet cloths to the neck, armpits and groin, because large blood vessels run close to the skin surface at these points and cooling them lowers core temperature quickly.

If the person is fully conscious and able to swallow safely, give cold water or a rehydration drink. Do not give fluids to someone who is confused or whose consciousness is impaired, as there is a risk of inhaling the fluid into the lungs. In either case, emergency services are not optional: they need to come.

First aid for heat stroke

1Call emergency services immediately, or have someone else call while you start cooling.
2Move the person to shade or an air-conditioned space without delay.
3Remove outer and excess clothing gently.
4Apply ice or cold wet cloths to the neck, armpits and groin.
5If fully conscious and able to swallow, give cold water in small amounts.
6Do not leave the person alone. Monitor their breathing until help arrives.

Prevention: protecting yourself in extreme heat

Prevention is far less costly than treatment. On extremely hot days, schedule any physical activity in the cooler hours, which are generally before 10 in the morning or after 4 in the afternoon. In Gulf states where peak temperatures exceed 45 degrees Celsius, even these windows can be dangerous for intensive outdoor work, particularly when high humidity prevents sweat from evaporating and cooling the body.

Regular hydration before thirst appears is essential. Thirst is a late signal that means the body has already started to dehydrate. Monitor your urine colour as a simple guide: pale and straw-coloured means good hydration, dark yellow or amber means you need more fluid. In extreme heat the body needs substantially more water than in temperate conditions.

Wear light-coloured, loose-fitting clothing made of breathable fabric that allows air movement across the skin. A broad-brimmed hat reduces direct sun load on the head, which matters because the head has a high density of blood vessels close to the surface.

If you work outdoors, taking rest breaks in the shade or a cool space every hour is not optional comfort, it is a physiological necessity. Gulf states have introduced formal midday break regulations for outdoor workers during summer months because the science supports this firmly. If your workplace does not enforce these breaks, that is a safety issue worth raising.

Acclimatisation matters more than many people realise. If you are moving from a cooler country or returning after a period away, plan for 10 to 14 days of gradually increasing exposure before working full hours in peak heat.

Protecting children and older adults

Young children do not reliably complain about heat before it becomes dangerous, and their small bodies lose water at a relatively higher rate than larger ones. Never leave a child in a closed car, even for a few minutes. Car interiors reach lethal temperatures within ten to fifteen minutes on a sunny day, even when the outside temperature seems manageable.

Older adults face a double problem. Their bodies are slower to detect rising heat and slower to produce adequate sweat in response. Many also take medications that affect heat regulation, including diuretics, cardiac drugs and psychiatric medications. Check in on elderly relatives and neighbours during peak heat periods, particularly those who live alone.

On days of extreme heat, help older relatives identify an air-conditioned place they can go to if their home is not cooled, such as a community centre, mosque or health clinic. A short visit or phone call can genuinely save a life.

What happens in hospital after heat stroke?

In hospital, doctors continue and accelerate the cooling using cold intravenous fluids, cooling blankets and in severe cases full ice bath immersion. A review by Dr Al Mahri and Bouchama, leading researchers in heat stroke, documented that prompt and effective cooling is associated with a clear reduction in deaths and long-term complications. The target is to reduce core temperature to below 39 degrees Celsius within 30 minutes of reaching the emergency department.

The organs most vulnerable to heat-related damage are the kidneys, liver, brain and heart muscle. Extreme heat damages proteins inside cells directly, and the resulting tissue injury triggers a systemic inflammatory response. Blood thickens with severe dehydration, raising the risk of clotting in blood vessels. Blood and urine tests monitor these organs continuously throughout treatment, and abnormal results may require specific interventions beyond cooling.

The majority of patients who reach hospital early and receive prompt cooling recover without permanent damage. But delay in cooling can leave lasting harm in the kidneys or liver or affect neurological function. This is the fundamental reason that first aid cooling begins at the scene and not in the waiting room.

After discharge, the body remains more sensitive to heat for weeks. Monitoring kidney function with a blood test in the weeks following a significant heat stroke episode is appropriate, and any return to outdoor work in heat should be gradual.

When to call emergency services without delay

Any person who has crossed from heat exhaustion into heat stroke needs emergency services and cannot be managed safely at home. The defining signs are confusion, failure to respond logically, or loss of consciousness. These are a genuine medical emergency and there is no reason to hesitate about calling. The cost of calling unnecessarily is minimal. The cost of not calling when needed can be a life.

Even someone who appears to recover from heat exhaustion should be watched for several hours, because symptoms can deteriorate suddenly. If the person improves clearly within 30 minutes of rest, cooling and hydration but then confusion or rising temperature returns, that is a signal for emergency services regardless of how well they seemed initially.

A person who has had heat stroke before is more vulnerable to future episodes and should be more careful during subsequent hot seasons. This means a proactive prevention plan each summer, earlier recognition of warning signs and a lower threshold for stopping activity and seeking shade or cooling.

Use Sihtak to log any heat-related symptoms you or a family member experience during summer months. If symptoms recur on hot days, a record of when and under what conditions they happen helps your doctor identify whether there is an underlying vulnerability that needs attention.

Frequently asked questions

What is the key difference between heat exhaustion and heat stroke?

The decisive difference is mental state. In heat exhaustion the person is tired and may feel sick but their thinking is clear. In heat stroke they become confused, irrational or unconscious. Heat stroke is a medical emergency requiring an ambulance. Heat exhaustion needs rest, cooling and fluids but can usually be managed without hospital care if the person responds quickly.

Can heat stroke happen in the shade?

Yes. The extreme ambient temperature itself is enough to cause heat stroke without direct sun exposure. Workers in hot enclosed environments such as commercial kitchens, boiler rooms or indoor construction sites face the same risk as those working in direct sunlight.

How much water should I drink in extreme heat?

In temperatures above 40 degrees Celsius with physical activity, the body may need more than a litre of water per hour. However, drinking very large amounts of plain water without any salt replacement can also cause problems. Water with a small amount of added salt or an oral rehydration solution is better for prolonged exposure than plain water alone.

Is cooling with cold water safe for someone with heat stroke?

Yes and it is recommended. Earlier concerns that cold water would cause blood vessel spasm have been refuted by current research. Immersion in cold water or applying ice to the neck, armpits and groin is the most effective available cooling method before hospital treatment begins.

Does coffee or tea increase the risk in heat?

Moderate amounts of coffee and tea do not cause meaningful dehydration. Very large amounts have a mild diuretic effect. In extreme heat, water is the safest drink for hydration. Avoid alcohol during hot weather as it impairs the body's ability to regulate temperature.

How long does recovery from heat stroke take?

Recovery varies with severity. Mild heat exhaustion may resolve in a few hours with rest and fluids. Full heat stroke often requires hospital observation for a day or more. Returning to outdoor work or exertion in the heat before full recovery significantly increases the risk of a second episode.

Can someone who has had heat stroke before do outdoor work again?

Yes, but with extra caution. A history of heat stroke is a risk factor for future episodes. Gradual acclimatisation, strict hydration, shorter work periods in peak heat and early recognition of warning signs all help reduce this recurrence risk.

Sources

This content is for health education only and is not a substitute for medical advice. If you have symptoms that worry you, see your doctor.