When we think about mental health disorders, most of us assume that, unlike physical disorders, they’re not contagious. However, around the year 2010, during a rash of teen suicides in Palo Alto, California, mental health experts explored that there could be a social contagion effect at work, which begs the larger question: are mental health disorders transmissible with teen social/peer groups?
Before we address that big-picture question, let’s take a look at the situation that happened in Palo Alto. In response to a phenomenon called a suicide cluster, the Centers for Disease Control (CDC) dispatched an Epi-Aid Team to investigate the circumstances that led six high school students to take their lives within several months of one another – an unusually high number in an unusually short period of time for a community of around 65,000 people.
The Palo Alto Cluster and Mental Health Among Teen Peer Groups
For background, the CDC and mental health experts indicate that with regard to suicide, especially among teens, the contagion effect can be real. What that means is that when a person is part of a teen social network or teen peer group and one of their peers attempts or commits suicide, their risk of suicide increases. However, upon investigation, the contagion effect is most often exacerbated by additional factors, and not the result of exposure to peer suicide alone.
Contributing factors – as reported by the CDC in the Palo Alto case and outlined in this community response plan – included the following:
- High levels of pressure from parents to excel academically
- Elevated levels of alcohol and substance use
- Bullying
- School truancy
- Risky sexual behavior
In addition to the presence of those risk factors, the CDC identified another significant contributing factor: the media. Investigators learned that while covering the teen suicides in Palo Alto, reports included:
- Sensationalized headlines
- Details about how and where the suicides occurred method
- Pictures of high school students in grief over the suicides
- Reductive accounts of circumstances around each suicide
- Open comments sections
The CDC concluded that a combination of the elevated risk factors in the Palo Alto community and problematic media reports contributed to the Palo Alto suicide cluster. That makes sense and explains the transmissibility of behavior related to mental health disorders – in this case, suicidality – among teen peer networks.
However, the question remains: in the absence of contributing factors such as exposure to peer suicide, academic stress, elevated alcohol/substance use, and high prevalence other risky teen behaviors, does exposure to mental health disorders among peers increase risk of subsequently developing a mental health disorder?
New Research: Mental Health and Teen Peer Groups
A study conducted recently in Finland called “Transmission of Mental Disorders in Adolescent Peer Networks” explored that exact question. Here’s how the research team framed the inquiry:
Is having peers with a mental disorder in the same social network during adolescence associated with later risk of mental disorder?
To answer this question, they analyzed data on over 700,000 people from the year they completed 9th grade until they received a diagnosis for a mental health disorder, left Finland, died, or reached the end of 2019, whichever happened first. Researchers analyzed data from late 2023 to early 2024 and published the study in May 2024.
Access to both public health and school records enabled the research team to determine the following:
- Baseline: The number of people with or without a mental health diagnosis in 9th grade
- Exposure: The number of classmates with a mental health disorder people without a mental health disorder had in 9th
- Outcome: Among people with a classmate or classmates with a mental health disorder, the presence of a mental health disorder at one year, two years, three years, four years, five years, or five or more years after 9th grade, expressed as a hazard ratio (HR).
We’ll clarify the terminology before we share the results. First, in this context, exposure means having a classmate or classmates diagnosed with a mental health disorder in 9th grade. Second, hazard ratio (HR) is a simplified way of reporting the increased risk of a specific outcome associated with exposure to a specific experimental variable. For instance, an HR of 1.0 indicates no increased risk, while an HR of 1.5 indicates a 50 percent increased risk.
Let’s take a look what the researchers found.
Exposure to Mental Health Disorder Among Classmates and Subsequent Mental Health Diagnosis
The results included data for specific mental health outcomes among 9th graders without a mental health diagnosis after exposure to one or more classmates with a mental health diagnosis at one, two, three, four, five, and five + years after 9th grade. We’ll report the hazard ratios below for each mental health outcome for one year, two/three years, and five years + after exposure.
First, substance use.
Substance Misuse Disorders
One year follow up:
- One classmate: 1.21 / Two or more: 1.02
Two and three year follow up:
- One classmate: 1.18 / Two or more: 1.30
Five years + follow up:
- One classmate: 0.97 / Two or more: 1.06
Notable results: 21% increased risk for exposure to one classmate after one year, 30% increased risk for exposure to two or more classmates after two-three years, and decreasing risk with increased time after exposure.
Next, we’ll look at mood disorders, which include diagnoses such as major depressive disorder (MDD) and bipolar disorders.
Mood Disorders
One year follow up:
- One classmate: 1.16 / Two or more: 1.40
Two and three year follow up:
- One classmate: 1.08 / Two or more: 1.08
Five years + follow up:
- One classmate: 1.03/ Two or more: 1.06
Notable results: 40% increased risk for exposure to two or more classmates after one year, decreasing risk with increased time after exposure.
Now we’ll look at anxiety disorders, which include diagnoses such as generalized anxiety disorders (GAD), social anxiety disorder (SAD), phobia-related disorders, and others.
Anxiety Disorders
One year follow up:
- One classmate: 1.10 / Two or more: 1.20
Two and three year follow up:
- One classmate: 1.04 / Two or more: 1.05
Five years + follow up:
- One classmate: 1.02/ Two or more: 1.01
Notable results: 20% increased risk for exposure to two or more classmates after one year, decreasing risk with increased time after exposure.
Next, we’ll look at eating disorders, which include diagnoses such as anorexia nervosa, bulimia nervosa, binge eating disorders, and others.
Eating Disorders
One year follow up:
- One classmate: 1.18 / Two or more: 1.55
Two and three year follow up:
- One classmate: 0.97 / Two or more: 1.02
Five years + follow up:
- One classmate: 1.19 / Two or more: 1.44
Notable results: 18% increased risk for exposure to one classmate after one year, 55% increased risk for exposure to two or more classmates after one year, decreasing risk at two-five years after exposure, but a 19% increased risk for exposure to one classmate and a 44% increased risk for exposure to two or more classmates at five or more years after initial exposure.
Finally, we’ll look at the impact on exposure to classmates with a mental health disorder in 9th grade on the risk of receiving any type of mental health diagnosis later in life.
Any Disorder:
One year follow up:
- One classmate: 1.09 / Two or more: 1.18
Two and three year follow up:
- One classmate: 1.00 / Two or more: 1.08
Five years + follow up:
- One classmate: 1.00 / Two or more: 1.03
Notable results: 18% increased risk for exposure to two or more classmates after one year, decreasing risk with increased time after exposure.
We’ll discuss these results below.
What Do These Results Mean?
There’s a question at the root of this study that everyone wants an answer to, but that’s not asked directly:
Are mental health disorders contagious?
The simple answer is no, mental health disorders are not contagious like the flu is contagious.
Evidence from the CDC indicates that a contagion effect exists for suicidality, which is not a mental health disorder itself, but is associated with several mental health disorders. The contagion effect with regards to suicide is simple to understand: the knowledge of suicide, especially within a family or close peer group, increases suicide risk.
In other words, when we talk about mental health/suicide and contagion, we don’t mean contagious in the way most of us think of the word, as in contagious like the flu. Here’s how the American Psychological Association (APA) defines the contagion effect:
“The spread of behaviors, attitudes, and affect through crowds and other types of social aggregates from one member to another. Early analyses of social contagion suggested that it resulted from the heightened suggestibility of members and likened the process to the spread of contagious diseases. Subsequent studies suggest that social contagion is sustained by relatively mundane interpersonal processes, such as imitation, conformity, universality, and mimicry.”
But there are two things about the study and results above that add to our knowledge of the contagion effect, or transmissibility of mental health disorders:
- They controlled for confounding factors that may contribute to the development of mental health disorders, such as family, school, and environmental factors.
- The length of time before follow up.
The first point suggests common risk factors did not impact subsequent mental health diagnoses, while the second point suggests it’s unlikely that things like imitation, conformity, and mimicry contributed to subsequent mental health diagnoses.
Conclusion: Exposure May Increase Risk
That’s the takeaway from the study. People who, in 9th grade, had a classmate or classmates with a mental health diagnosis, were at increased risk of receiving a subsequent diagnosis for the following types of mental health disorders:
- Mood disorders
- Anxiety disorders
- Eating disorders
The study authors describe the results as follows:
“The findings of this study suggest that mental disorders might be socially transmitted within adolescent peer networks.”
The key phrase there is “might be socially transmitted.” While we know there’s not a transmissible pathogen that causes mental health disorders, like the virus that causes the flu, several elements of the data are impossible to ignore:
- 40% increased risk in mood disorder diagnosis one year after exposure to two or more classmates with a mental health diagnosis.
- 18% increased risk of any mental health diagnosis one year after exposure to two or more classmates with a mental health diagnosis.
- 20% increased risk of anxiety diagnosis one year after exposure to two or more classmates with a mental health diagnosis.
- 55% increased risk of eating diagnosis one year after exposure to two or more classmates with a mental health diagnosis.
- 44% increased risk of eating diagnosis more than five years after exposure to two or more classmates with a mental health diagnosis.
We know mental health disorders are not transmissible in the way bacterial or viral pathogens are transmissible. Nevertheless, the data above mean we need to provisionally accept the assertion made by the researchers in Finland. Mental health disorders might be transmitted within teen peer groups. The emphasis is on might be, but the data, as we mention above, are impossible to ignore.
