Abstract
Over the last ten years, several mental health indicators, such as anxiety, depression and eating disorders, have deteriorated in the populations of several Western countries, including France. Adolescents and young adults are particularly affected by these disorders, which is why mental health has been chosen as a "Grande Cause Nationale" for the year 2025. At the same time, digital uses, particularly those of adolescents and young adults, have intensified and transformed, with social networks becoming a major part of daily lifestyles. This raises the question : are social networks responsible for the increase in mental health disorders ? This involves determining whether or not there is a causal link between these two concomitant phenomena. Demonstrating this is no easy task for the scientific disciplines tackling the issue. Among them, epidemiology is in a position to shed a particular light, provided that it exploits the strengths theorized during the second half of the 20th century, and updates them for the future XXthcentury, and updating them to meet this new challenge. Through several examples of recent research, this lecture will aim to present the conceptual and methodological obstacles that prevent us, to date, from answering the question posed with certainty, as well as the solutions that epidemiology must implement to achieve this.
