In summary: Heatstroke is not a bad case of sunstroke. It is a medical emergency. Body temperature above 40°C, confusion, and absence of sweating are the warning signs. If you see them, call 112. Prior hydration is the best way to avoid reaching that point.
Heatstroke: symptoms, when it's an emergency, and how to prevent it with hydration
The summer of 2022 was the deadliest in recent European history. According to a study published in The Lancet Regional Health, that summer caused more than 61,000 heat-attributable deaths across the continent. In Spain, more than 4,600. Most of those deaths were not inevitable. They were the result of failing to recognise in time what was happening.
Heatstroke has clear symptoms. It has a concrete response protocol. And it has known risk factors. This article is about exactly that: what it is, how to recognise it, when to call 112, and what role hydration plays in preventing it.
Heat exhaustion and heatstroke are not the same thing
This distinction matters because it determines what to do next.
Heat exhaustion is the precursor. Body temperature rises between 37 and 40°C. The body is still trying to regulate itself: it sweats heavily, the skin is damp and cool, the person feels weak, dizzy, nauseous. There may be headache and muscle cramps. At this stage, the situation is manageable if you act: move the person somewhere cool, give them small sips of water, loosen their clothing. Most people recover without urgent medical intervention.
Heatstroke is a different matter. Temperature exceeds 40°C and the body's thermoregulatory mechanism has failed. There are two types. In classic heatstroke, which mainly affects elderly people or those with chronic conditions during prolonged heatwaves, the skin is hot and dry because the body has stopped sweating. In exertional heatstroke, which occurs in athletes and physical labourers, sweating may still be present. In both cases, what never fails to appear is mental confusion. If the person is disoriented, speaking incoherently, or not responding normally, you are no longer dealing with exhaustion. You are dealing with an emergency.
Heatstroke symptoms you should not ignore
The defining signs of heatstroke are body temperature above 40°C, altered level of consciousness (confusion, disorientation, incoherent responses or agitation), hot and flushed skin (dry in the classic type, damp in exertional), rapid and strong pulse, and nausea or vomiting.
In more severe cases, loss of consciousness and convulsions appear. When there are convulsions or the person loses consciousness, the time until the ambulance arrives can determine whether there are permanent consequences or not.
One detail people do not always know: in classic heatstroke, the absence of sweating alongside very high temperature is a specific warning sign. If the skin is dry and hot and the person is confused, there is nothing to wait for. Call 112.
When to call 112
The answer is: when there is any sign of mental confusion or loss of consciousness. Not when you are certain. Not after you have waited ten minutes to see if they improve. Immediately.
Three specific situations that justify calling 112 without hesitation. The person does not respond normally to simple questions. The person loses consciousness even briefly. Temperature exceeds 40°C and does not come down with immediate cooling measures.
A common mistake is trying to give water to someone who is confused or unconscious. If they cannot swallow safely and consciously, the risk of aspiration is real. Do not give oral fluids if there is any altered level of consciousness.
First aid while waiting for the ambulance
The goal is to lower body temperature as quickly as possible. Every minute that temperature stays above 40°C increases organ damage.
The steps are: move the person somewhere cool (an air-conditioned interior if available, shade if not), loosen or remove clothing, apply cold water to the skin using cloths or by spraying, and place ice packs or cold compresses on areas with the greatest blood flow: armpits, neck, and groin. If the person is conscious and can swallow safely, offer small sips of cold water. If they are unconscious or not responding well, place them in the recovery position and do not attempt to give anything orally.
On medication: neither aspirin nor ibuprofen. In heatstroke, the high temperature is not an infectious fever. Conventional antipyretics do not act on the mechanism of thermoregulatory failure and can complicate the situation.
This article is for informational purposes. In an emergency, always call 112. It does not replace medical judgement.
You can consult the full first aid protocol for heatstroke from Cruz Roja España for more detail on each step.
Who is most at risk
Risk is not evenly distributed. People over 65 have reduced thermoregulatory capacity and tend to feel less thirsty, which means they can reach states of severe dehydration without noticing. Babies and young children cannot communicate their symptoms clearly and depend entirely on someone else to detect the signs for them.
People with cardiovascular disease, kidney conditions, or diabetes have a compromised response to heat stress. Athletes and outdoor workers generate internal heat from muscular effort on top of ambient heat, which accelerates the process. And there is a group that is often overlooked: people taking diuretics, first-generation antihistamines, or certain antipsychotics, because these drugs reduce sweating or increase fluid loss. If someone in your life falls into any of these groups and spends time in the sun during summer, it is worth making sure they know these symptoms.
Hydration as prevention, not as cure
Once heatstroke has begun, oral hydration does not stop it. The damage is already happening and requires external cooling and medical attention. Where hydration does have a decisive role is in prevention: keeping the body in conditions to thermoregulate properly before the situation gets out of hand.
The mechanism is straightforward. Sweating is the body's cooling system. To sweat, the body needs water. If you are dehydrated, you produce less sweat, temperature rises faster, and the heatstroke threshold is reached sooner. As the World Health Organization explains in its fact sheet on heat and health, dehydration is one of the main factors that increase vulnerability to heatstroke.
The problem is that thirst is a late signal. By the time you feel it, you have already been dehydrated for a while. Drinking before going out into the heat, not just when you get there, is the difference between maintaining thermoregulatory capacity or starting exercise or outdoor activity already at a deficit.
On hot days with physical activity, the general recommendation is to take in between 500 and 700 millilitres per hour during exertion. In activities lasting more than an hour with heavy sweating, replacing only water without salts can lead to mild hyponatraemia: a drop in blood sodium that causes fatigue, headache, and in serious cases confusion. The right balance includes some sodium, which can come from food, electrolyte drinks, or rehydration salts in prolonged situations.
To recognise whether you are drinking enough before heat becomes a problem, there is more detail in our guide on signs that you are not drinking enough water. And if you are looking for a bottle that works well through summer, the best water bottles for summer covers the options that actually handle the heat.
Preparation is easier than recovery
Heatstroke is an emergency that can be prevented in most cases with information and habits that are not complicated. Recognising the difference between exhaustion and emergency. Knowing when to call 112 without waiting until you are certain. Drinking water before feeling thirsty, especially on hot days or during physical activity.
Summer heat is not going to get gentler. Heatwaves are more frequent and more intense. Preparation needs to move in the same direction.
If you want to start with something concrete, a water bottle that keeps things genuinely cold during the hottest hours is part of that preparation. You can see what we have in the full Fluye collection.
Written by the Fluye Bottle team