With the arrival of heat waves, streets, beaches and public transport become a perfect breeding ground for a horrible fainting or heat stroke to occur. Something that is not too isolated, since in 2025 alone high temperatures were behind 3,832 deaths in Spain, a number that tragically exceeds those killed in traffic accidents.
An emergency. Many of these heat-related problems begin with something that can go unnoticed, such as heat syncope or lipothymia, which presents as dizziness with blurred vision and, in a matter of seconds, total disconnection. Given this, the question is obligatory: what exactly happens in our body that makes our brain decide to “turn off”?
The reason. To understand why we faint, we must go to the European Society of Cardiology, which in its official guide defines syncope as a temporary loss of consciousness due to less blood flow reaching the brain for a few moments.
To understand it, when we are exposed to high temperatures, the human body activates its basic cooling mechanism, which is the dilation of its blood vessels. The goal here is to dissipate heat and cool us down, and that’s why it’s easy to see how people turn red in the heat and also feel weaker from the drop in blood pressure.
And there is more. If we add to this drop in tension the stress of standing for a long time without moving or dehydration, blood tends to accumulate in the legs due to the effect of gravity. This causes the heart to not be able to pump enough blood upwards and the brain, being momentarily deprived of oxygen and nutrients, activates its emergency system, which is fainting. When falling to the ground, the horizontal position cancels the effect of gravity, allowing blood flow to return to the brain and the person to regain consciousness.
Different terms. One of the most common mistakes is to put all the health problems that they cause us in the same bag and it is important to differentiate them in the following three situations:
- Heat syncope: It is a brief fainting due to the “sequestration” of blood in the extremities due to vasodilation and dehydration, and which does not usually leave serious consequences if there is no serious contusion and recovery is rapid.
- Heat exhaustion: This is a systemic condition that occurs when the body loses a lot of fluid through sweat. It is characterized by extreme weakness, nausea, headache and sweaty skin, but with the difference that there is no serious neurological alteration.
- Heat stroke: This is a vital medical emergency that threatens a person’s life, since the body’s thermostat collapses. In this situation, the core temperature reaches or exceeds 40°C and severe nervous system dysfunction occurs with delirium, seizures, and even coma.
The risk factors. There is a great cocktail of situations that predispose us to some of these situations, such as heavy meals. After a summer feast, the body redirects a large amount of blood flow to the digestive system to process the food. With the vessels already dilated by the heat, the brain is left with a very narrow margin of blood supply. This means that a little physical activity here can lead to dizziness or fainting, making light meals almost an obligation in summer.
Age is also important to take into account, since the people most vulnerable to any of these medical situations are those over 65 years of age. And it is only because aging attenuates the thirst reflex and slows down the body’s vasomotor response, which causes many people to become dehydrated without ever feeling the need to ask for a glass of water.
The recommendations. To avoid reaching a situation of this type, it is important to maintain good hydration throughout the day, emphasizing vulnerable people who should drink despite not being thirsty. In addition, avoid going outside during critical hours of the day with higher temperatures or having light meals to avoid straining the body much more in the face of high temperatures.
Images | Gerardo Ramirez Lopez
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