A landmark study from Finland, released today, suggests that teenagers whose peers have been diagnosed with a mental health condition are more likely to receive a similar diagnosis themselves. The research, which analysed data from more than 600,000 young people born between 1985 and 2000, found evidence supporting the concept of “social transmission” of mental health conditions among adolescents. However, researchers emphasise that this does not mean mental illness is contagious like an infectious disease, and that genetic predisposition and environmental factors also play crucial roles.
Rising Mental Health Challenges Among Youth
Globally, depression and anxiety rates are climbing among young people. In Australia, recent data shows anxiety rates have surged from 13% to 28% over the past 15 years, while suicide attempts have doubled. Despite increased awareness and expanded mental health services, young people are facing more severe and complex mental health challenges than ever before. Both family and peer relationships are known to significantly influence mental health, with genetic and environmental factors each uniquely shaping the development of conditions.
What the Finnish Study Found
The study, conducted by researchers in Finland, used nationwide health records and school enrolment data to examine the link between peer mental health and individual diagnoses. Key findings include: having a peer with a diagnosed mental health condition—or a peer with a family history of one—increases the likelihood of receiving the same diagnosis; and the effect was stronger among peers attending the same school rather than living in the same area, particularly in later adolescence. The authors conclude that these findings support the idea of “transmission” of mental health risk during adolescence.
Important Caveats: Not Contagion
It is crucial to understand that terms like “transmission” or “contagion” are not used in the same sense as for infectious diseases. You cannot “catch” a mental health condition. Instead, these terms describe how emotions, behaviours, and social norms can spread among peers over time, influencing mental health. For example, increased awareness and reduced stigma within a peer group may encourage help-seeking, though the study did not test this. Peer relationships and genetic risk are part of a complex mix of factors shaping adolescent mental health. Because the study defined peers by school year or location, findings likely reflect shared school and community influences, such as school culture, educational approaches, and neighbourhood features like green space.
What the Study Could Not Measure
The study’s size is a key strength, but using register data imposes limitations. The data cannot confirm whether individuals actually knew each other or were friends; “peer networks” were defined by school (same grade and birth year) or location (same postcode and birth year). Genetic risk was inferred from family diagnoses, not DNA, and many mental health conditions may go undiagnosed. The study accounted for sex, age, and parental income and education, but not for gender identity, ethnicity, school environment, or lifestyle behaviours such as smoking, alcohol use, or exercise. Additionally, the study found that having a peer with a family history of a condition like substance use disorder increased one’s own diagnosis risk, but the data cannot capture other explanatory factors, such as shared social environments.
Implications for Schools and Future Research
This study shows that both peers and family risk are linked to adolescent mental health, but it cannot explain how these effects occur. Future research needs to disentangle peer selection (choosing similar friends) from peer influence (how friends shape each other). The importance of school environments is clear: school-based mental health programs that harness peer influence are key. In Australia, the Mind your Mate program has shown promise in lowering depression risk in teens by educating them about mental health and how to support peers. These findings point beyond individuals to the wider environments young people inhabit. Improving adolescent mental health ultimately requires investing in the people and places around them, including the schools and communities where peer relationships develop.
Thank you to Professor Cath Chapman for her role in developing this article.
If this article has raised issues for you, or if you’re concerned about someone you know, call Lifeline on 13 11 14. Aboriginal and Torres Strait Islander people can also call 13YARN on 13 92 76.
