With the arrival of heat waves, streets, beaches, and public transport become breeding grounds for serious health issues like fainting or heat stroke. In fact, in 2025, high temperatures were responsible for 3,832 deaths in Spain, a figure that tragically surpasses those lost in traffic accidents.
An Emergency Situation
Many heat-related problems start unassumingly, such as heat syncope or lipothymia, which can present with dizziness, blurred vision, and can lead to complete disconnection within seconds. This raises an important question: what happens in our bodies that makes our brain decide to “turn off”?
The Biological Mechanism
According to the European Society of Cardiology, syncope is defined as a temporary loss of consciousness caused by a decrease in blood flow to the brain. When exposed to high temperatures, the human body activates its primary cooling mechanism—dilating the blood vessels to dissipate heat. This can cause individuals to look flushed and feel weaker due to lowered blood pressure.
The Role of Gravity
If we consider other factors like standing still for a long time or dehydration, blood can accumulate in the legs due to gravity. This further complicates the situation by reducing the heart’s ability to pump blood upwards, depriving the brain of necessary oxygen and nutrients, thus triggering fainting. When a person falls, the horizontal position negates gravity’s effects, allowing blood flow to return to the brain and restoring consciousness.
Differentiating Heat-Related Conditions
It’s essential to differentiate between heat-related medical conditions:
- Heat syncope: A brief fainting caused by blood sequestration in the extremities due to vasodilation and dehydration. Recovery is usually quick and without severe consequences.
- Heat exhaustion: A systemic condition arising from significant fluid loss through sweat, characterized by extreme weakness, nausea, headache, and sweaty skin, but without serious neurological effects.
- Heat stroke: A critical medical emergency where the body’s thermostat fails, leading to a core temperature exceeding 40°C, along with severe nervous system dysfunction.
Risk Factors
Several factors predispose individuals to these health risks, such as consuming heavy meals. After a summer feast, blood flow redirects to the digestive system, further complicating the situation when combined with heat-induced vasodilation. Consequently, even minimal physical activity can trigger dizziness or fainting, making light meals essential during summer.
Age and Vulnerability
Age is a critical factor—individuals over 65 are among the most vulnerable due to diminished thirst reflexes and slower vasomotor responses, often leading to dehydration without the sensation of needing water.
Recommendations for Prevention
To avoid heat-related issues, staying hydrated throughout the day is crucial, especially for vulnerable populations who must drink—even when they don’t feel thirsty. Additionally, minimize outdoor activities during peak heat hours and opt for lighter meals to lessen the strain on the body during hot temperatures.
Images | Gerardo Ramirez Lopez