As they do every year, health authorities launch an active surveillance program between June 1 and September 15 to monitor the population’s exposure to heat waves during the summer season, in close collaboration with Météo France. A prevention initiative is also being implemented by the Ministry of Health and Santé publique France, reminding the public of the proper precautions to take to protect their health and care for those around them during periods of extreme heat.

Since the summer of 2023, and 15 days after the end of each heatwave episode (the time required to consolidate approximately 90% of INSEE data reports), a dedicated epidemiological update includes an initial estimate of the excess mortality from “all causes” observed during a heatwave episode. These results provide an initial estimate of the excess all-cause mortality during the heatwave, which will be refined by more robust estimates in the final report on the summer surveillance period prepared in the fall.

Three questions for Robin Lagarrigue, scientific researcher at the Health, Environment, and Work Directorate of Santé publique France

What are the distinctive features of this first heatwave episode?

Mainland France experienced a heatwave in late June and early July across nearly its entire territory, notable for its duration and early onset. Between June 19 and July 6, 60 departments across all mainland regions—with the exception of Normandy—were affected by a heatwave,¹ representing 74% of the mainland population.

The early onset of this heatwave is linked to specific exposure contexts (particularly at school and at work) as well as reduced acclimatization to high temperatures. The duration of the heatwave is also a distinctive feature of this episode. The average number of heatwave days was 5, but varied by department, ranging from 3 to 12 days.

This episode is reminiscent of the early heatwaves of June 2019 and 2022, which were also subject to red heatwave alerts. However, comparing these episodes remains challenging and requires caution, as the areas affected intensely and over a long period are not the same, and exhibit different levels of heat vulnerability.

What do the figures published in this epidemiological bulletin mean?

Santé publique France is publishing an initial estimate of excess “all-cause mortality” for the departments affected by the first heatwave of the summer of 2025. Over the periods and in the departments affected by the heatwave, at least 480 excess “all-cause” deaths (+5.5%) were estimated (mortality data as of July 22). People aged 75 and older account for the majority of this preliminary toll, with 410 excess “all-cause” deaths (+6.7%) in this age group. The region with the highest departmental excess deaths is Provence-Alpes-Côte-d’Azur (PACA), with 140 excess deaths from “all causes” (+9.2%). As of the data cutoff date, three regions showed no excess all-cause mortality during the heatwave days (Corsica, Hauts-de-France, and Île-de-France).

How should this initial estimate of excess mortality be interpreted?

This initial estimate was obtained by comparing the “all-cause” mortality observed during this first heatwave episode with an expected “all-cause” reference mortality, modeled over the same period (Euromomo method). This is an initial, unconsolidated estimate 15 days after the heatwave episode, based on the nationwide reporting of non-exhaustive mortality data from civil registry offices, transmitted by INSEE (consolidation after 1 month).

These deaths occurring during the heatwave days can be explained by various factors, primarily the impact of the heat—particularly its duration and, in some cases, significant intensity depending on the department. Other events can also affect mortality (epidemics, accidents, etc.) and are taken into account in this estimate. Thus, this excess mortality can be largely attributed to the population’s exposure to heat, but not exclusively.

For this reason, Santé publique France has additionally developed a method to estimate, at the departmental level, “all-cause” mortality attributable to the general population’s exposure to heat, for all ages and for people aged 75 and older. The objective is to illustrate the contribution of the general population’s exposure to heat to all-cause mortality, as well as its spatial and temporal trends. These data on attributable mortality require consolidated mortality data and are published in the summer season report in the fall.

These figures should prompt us to remain highly vigilant; heat remains more than ever a health risk in the context of climate change—even outside of heatwave periods—requiring the implementation of prevention and management measures to mitigate the impact of heat on the population, as well as the need for a strengthened climate change adaptation strategy at both the national and regional levels.

Learn more:

• Summer 2025: Health authorities remind the public of the right steps to take to protect themselves from extreme heat

• Heat waves: the government is taking action to protect the public and prepare communities

• What measures can be taken to prevent heat-related risks?

• Our thematic dossiers:

  • Extreme heat, heat waves

  • Drowning

  • UV

  • Skin cancer