Heat waves, droughts, fires... The month of July 2026 has become the hottest and one of the driest ever recorded in France since measurements began in 1900, Météo-France announced on Tuesday August 4. With an average temperature of 24.9°C, last month erased the previous records of the heatwave of August 2003 (24.8°C) and July 2006 (24.4°C).
These exceptionally high temperatures are not without consequences for our health and can, in the most serious cases, lead to death. During the heatwave at the end of June, of historic intensity, France recorded the highest excess mortality linked to a heatwave since 2003. According to figures from Public Health France, published on July 22, 5,764 excess deaths were recorded between June 17 and July 2.
The body regulates its temperature...
To understand the harmful effects of this extreme heat on our body, we must first understand how our body functions in the face of it. Our body must remain at a temperature around 37°C. To achieve this, the internal thermostat located in our brain, the hypothalamus, constantly monitors its balance. “When it detects an increase in body temperature, it activates a series of mechanisms to keep it within acceptable limits,” explains Doctor Laurène Bruvy, general practitioner in Amiens (Somme). It first triggers the dilation of blood vessels, called vasodilation, which increases blood flow and thus helps promote the evacuation of heat to the outside.
Sweating helps cool the body. Finally, the latter naturally encourages us to reduce physical efforts, which increase heat production. “This is why doing sport is not recommended. The body is more dehydrated and, in general, people do not compensate for the loss of water during sport. The muscles also use more energy and this tires the body, causing additional stress for the body,” explains Laurène Bruvy.
...But up to a certain point
But the thermoregulation process reaches its limits during high heat waves. Sweating becomes less effective when air humidity is high, because it is more difficult for sweat to evaporate. The body then continues to produce sweat without being able to reduce its temperature. According to Public Health France, dehydration is also one of the main risks linked to high heat. Heavy sweating causes a loss of water and mineral salts, which can disrupt the functioning of the body. Lack of water notably reduces the body's ability to maintain a stable temperature.
According to the World Health Organization (WHO), episodes of extreme heat can aggravate certain cardiovascular and respiratory diseases, particularly in the elderly or those already suffering from chronic pathologies. “With heat, the blood vessels are more dilated, so the heart pumps more and increases cardiac output. It is therefore quite dangerous for people with heart disease,” underlines the general practitioner, supporting the fact that the heart must increase its activity in order to maintain sufficient circulation.
The risk of “cumulative thermal stress”
When these mechanisms are no longer sufficient, the internal temperature of the body increases and can cause heatstroke. “The symptoms that should alert you are fatigue, dizziness, migraines, a feeling of not being refreshed or discomfort,” specifies Laurène Bruvy. The Ministry of Health recalls that this phenomenon constitutes the most serious form of heat-related disorders: in the most serious cases, it can lead to death. The length of the episodes also plays a major role. According to Météo-France, the increase in the frequency and duration of heat waves is one of the consequences of climate change.
However, when temperatures remain high for several days or even weeks, particularly at night, the body recovers less well. “Fatigue accumulates while the ability to concentrate decreases. In the most serious situations, disturbances of consciousness may appear,” explains the doctor. Public Health France emphasizes that hot nights can also disrupt sleep and therefore increase fatigue, which increases vulnerability to extreme heat. According to the WHO, prolonged and repeated exposure to heat waves creates “cumulative heat stress” which increases the risk of illness and death. “Repeated dehydration can also weaken the functioning of the kidneys, particularly in vulnerable people,” says Laurène Bruvy.
Hydrate regularly without waiting to feel thirsty
Not all people are equal when it comes to extreme temperatures. According to the WHO and Public Health France, the elderly, infants, people with chronic illnesses or taking certain medications are among the populations most at risk, because their bodies may be less effective in regulating temperature or compensating for water loss. To protect yourself from extreme heat, Laurène Bruvy recommends regular hydration with water, around 1.5 liters per day, without waiting until you are thirsty. “Above all, do not drink sugary drinks which do not provide optimal hydration,” she warns, adding that you should also avoid alcohol.
It is also important to cool down using misters, wet wipes, a fan or even showers. "You should avoid taking them cold. Otherwise, the person's body temperature drops too quickly and causes thermal shock. It's counterproductive," insists the doctor. Finally, it is important to maintain a diet despite the absence of appetite and to adapt your environment, with the shutters closed for example, in order to maintain freshness, particularly in the bedroom, to improve falling asleep.
