Have you ever observed someone else laughing and felt the urge to smile yourself? Or been in a quiet crowd that quickly turns frustrated or panicked? Whether you are at work, with friends, or at home, your emotional states and behaviors are likely impacted by the state of those around you.¹

Social contagion is often automatic and depends on underlying mechanisms that may unfold below conscious awareness. While conscious deliberation can sometimes play a role, much of social contagion is driven by implicit cognitive mechanisms that operate without intentional thought.

For a behavior, emotion, or idea to catch on, we notice and attend to what others are doing, subtly perceive these actions as relevant or desirable, and often require reinforcement from multiple sources before adopting new behaviors. In some cases, a single exposure may be enough to trigger imitation (simple contagion), while in others, repeated exposure or encouragement from several peers is necessary (complex contagion). Social connections and the broader environment interact to determine how (and if) behaviors or emotions will spread through a network.⁴

Personal traits also determine how we interpret and react to social cues and the influence of those around us. A highly empathetic individual may quickly mirror the emotions of others and facilitate the spread of moods within a group. At the same time, a more apathetic person may be less affected and slow the effect of social contagion.

One of the earliest contributors to the concept of social contagion theory was Gustave Le Bon, a French social psychologist. Le Bon identified three main psychological processes that drive crowd behavior:

• Anonymity: The sense of being lost in the crowd diminishes personal responsibility and encourages individuals to act in ways they otherwise wouldn’t.²
• Contagion: The rapid spread of emotions and actions across a social network, similar to a “collective trance.”²
• Suggestibility: The heightened openness to influence and suggestion. Suggestibility allows “groupthink” to emerge and dominate individual judgment.²

Within Le Bon’s theory, one of the most important concepts is imitation (copying the behaviors, emotions, or attitudes observed in others). This process allows individual responses to ripple outward and contribute to a collective pattern of behavior. Social contagion theory has been widely applied in public health, marketing, education, and organizational psychology to understand how group behaviors and ideas spread.³

Social learning theory and social contagion

Social learning theory is highly relevant to social contagion. Developed by Albert Bandura, the theory claims that individuals acquire knowledge and behavior through direct experience and by observing, imitating, and interacting with others in a social context. Much like theories relating to social contagion, Bandura emphasized that learning is shaped by the dynamic interplay between environmental influences, and personal factors (such as cognition and emotions).

Norm Formation: The process by which groups develop shared standards for and expectations of behavior. Social norms guide and constrain behavior, and can emerge through socialization, peer influence, and interactions with authoritative figures. 

Bandwagon effect: The psychological bias in which individuals adopt certain behaviors, beliefs, or preferences because they perceive others doing the same. This effect can be driven by a desire for group belonging and prioritization of the collective over individual preferences and values. 

Behavioral Transmission: The movement of behaviors, emotions, or ideas from one individual to another within a social context. This concept is central to social contagion, as it describes how influence and information flow through networks.

Suggestibility: The tendency to be influenced by the behaviors of others. Higher susceptibility to suggestion increases the likelihood that individuals will adopt what they observe in their social environment.

Gustave Le Bon began the discussion on social contagion in the late 19th century with his seminal work, The Crowd: A Study of the Popular Mind. Here, he introduced the idea that behavior, emotions, and ideas can spread rapidly and unconsciously through groups, much like a contagious illness. He largely focused on crowds, where he proposed that people lose their sense of individuality and become susceptible to collective emotions and actions. Le Bon’s work laid the foundation for later theorists in the 20th century to refine the concept and apply it to broader social phenomena such as social movements and viral trends.²

Le Bon argued that crowds possess unique psychological laws, distinct from those of individuals. He identified "contagion" as a key mechanism by which emotions and actions propagate within groups. The theory rests on the idea that crowd behavior grows from unconscious reactions rather than conscious, deliberate thought. Le Bon was inspired to develop his theory from the dramatic social and political upheavals of the late 19th century. From the French Revolution to the revolutions of 1848, he observed the rising power of crowds to change society, including the penchant for impulsive, emotional, or even violent behavior.¹

Social contagion grew as a concept with the work of Sigmund Freud, the father of psychoanalysis. Building on Le Bon’s work, he attempted to explain how unconscious tendencies bypass consciousness in group formations. For example, Freud observed that in group settings such as crowds, members may unconsciously identify with the group leader and set aside their personal values and judgment.⁵

To explain the underlying mechanisms behind social contagion, Freud used the ideas of libido and identification in Group Psychology and the Analysis of the Ego (1921). For example, Freud argued that groups are bonded by “libidinal bonds,” or emotional energy associated with feelings of love and affection, which redirect individual aims toward the group or its leader.  In doing so, Freud expanded upon Le Bon’s psychological distinctions between the conscious and unconscious in group formation, contributing to his own theory of group psychology.⁵

Social contagion extended beyond psychology and was further developed by American sociologists in the 1930s and 40s. These researchers applied the concept to a wide range of social phenomena beyond crowds, offering more nuanced explanations of the drivers behind collective behavior. Robert Park introduced the concept of circular reaction, describing how social unrest and emotions move back and forth among group members, creating a feedback loop that amplifies collective impulses.

Additionally, Herbert Blumer reinterpreted the concept of social contagion within a sociological framework through his theory of collective behavior. He distinguished between elementary forms of collective behavior (such as mobs, panics, and stampedes) which lack established norms and are driven by spontaneous emotions. He contrasted these with more organized forms (like social movements and reforms) where updated rules and norms begin to shape collective action. Modern theorists broadened contagion theory from a singular focus on irrational mob violence to a comprehensive framework to explain a broad range of collective phenomena.⁴

In the years since, social contagion has been applied across a wide variety of fields, from public health to consumer behavior. This includes negative phenomena like violence and mass hysteria as well as the spread of positive behaviors through social networks. Researchers continue to leverage social contagion theory to design interventions and study human behavior, such as developing more effective strategies for spreading health education programs within closely connected communities.¹

Gustave Le Bon

French physician and social psychologist who pioneered the study of crowd psychology and social contagion. In The Crowd: A Study of the Popular Mind (1895), Le Bon introduced the concepts of anonymity, contagion, and suggestibility to explain how individuals in crowds adopt collective emotions and behaviors.¹⁸

Sigmund Freud

Austrian neurologist and founder of psychoanalysis, Freud expanded Le Bon’s ideas in Group Psychology and the Analysis of the Ego (1921). He explained social contagion through unconscious emotional bonds and identification with group leaders, deepening the psychological understanding of group dynamics.¹⁹

Robert E. Park

American sociologist and key figure in the Chicago School, Park advanced Le Bon’s theories by introducing the idea of "circular reaction," where emotions and behaviors are reinforced within groups. His empirical work on urban life and collective behavior established social contagion as a core concept in sociology.

Herbert Blumer

American sociologist and student of Park, Blumer further developed contagion theory by distinguishing between spontaneous collective behaviors (like mobs and panics) and organized social movements. He emphasized how group emotions and actions intensify through interaction, shaping modern sociological approaches to collective behavior.²⁰

Social contagion has introduced a new perspective to the field of behavioral science by helping us understand how thoughts and behaviors spread within groups. The theory both deepens our understanding of human psychology and informs practical strategies for shaping collective outcomes through interventions. Its influence informs practical approaches across various sectors, from public health to marketing and more.

Public Health and Health Behavior

In the face of modern challenges such as smoking cessation, vaccination uptake, and exercise habits, social contagion theory has been instrumental in designing public health campaigns and interventions that leverage the positive power of peer influence.

For instance, public health organizations target influential individuals or groups to embed new social norms for health behavior, such as mask-wearing or encouraging others to cover their coughs or sneezes.⁷ These strategies build upon the understanding that behaviors have a ripple effect through social networks, similar to diseases. Vaccination behavior, too, has been shown to be widely shaped by social networks and norms, which makes social norm interventions a particularly promising area.⁶

Additionally, social contagion can improve motivation and uptake of behaviors critical for well-being, such as exercise. A large-scale study published in Nature Communications analyzed data from over 1.1 million runners worldwide to show that exercise behaviors are socially contagious. The research found that when our friends exercise more, we are also more likely to increase our activity levels. While the “contagiousness” varied by activity level and gender, the study provided evidence that targeting social network structures can amplify the spread of healthy behaviors.⁸

Digital communication and social media

In today’s digitally-driven society, where social media is one of the most popular sources of information,⁸ social contagion theory is central to understanding how information spreads rapidly on digital platforms.

This extends to viral trends, misinformation, and emotional responses to content that can all spread rapidly and on an international scale. Particularly, misinformation online is often driven by highly emotional narratives, which naturally generate a charged response from viewers. Strong emotions drive users to share content more widely, amplifying the spread of fictitious narratives. This propagation can profoundly impact political campaigns, health behaviors, individual belief systems, and beyond.⁹

 In fact, the World Economic Forum’s Global Risks Report 2025 names misinformation and disinformation as a pressing risk for multiple regions, including the US, UK, Asia, and South America. This is even more concerning now, thanks to the rise of AI-generated fake narratives and the decline of fact-checking on social media. Such trends could have concerning ramifications for society, from eroding confidence in governments to heightened civil unrest.

Organizational behavior

Organizations can leverage social contagion to foster positive workplace cultures, encourage innovation, and manage change. Attitudes, work habits, and even emotions like enthusiasm or burnout can spread between employees, influencing overall productivity and morale. For example, research shows that when an employee is rated highly for managing relationships, their direct colleagues are 37% more likely to adopt the same behavior, with the influence persisting (though weaker) among colleagues two or three degrees removed.¹⁰

Peer-to-peer contagion is particularly powerful, often exceeding the influence of top-down leadership. Employees are more likely to adopt positive mindsets and embrace change when they observe their peers doing so. For example, peer-led initiatives, such as wellness programs or diversity and inclusion efforts, often rely on influential employees to model desired behaviors, which then spread throughout the organization.¹¹

While social contagion theory has significantly advanced our understanding of how behaviors and ideas spread, researchers continue to grapple with questions about its mechanisms, limitations, and social implications.

Correlation vs. causation: the homophily problem

One of the most persistent controversies concerns the classic debate in behavioral sciences of distinguishing correlation from causation. Researchers have debated whether observed similarities in social networks are truly the result of contagion or simply reflect homophily, or the tendency for people to associate with others who are already similar to themselves.

Studies claiming to show contagion, such as those on obesity or happiness, may actually be capturing pre-existing similarities or shared environments, rather than genuine interpersonal influence. For example, in one controversial study, Christakis and Fowler claimed that obesity could “spread” through social networks much like an infectious disease. However, statisticians have highlighted the extraordinary difficulty of distinguishing contagion from homophily, challenging the validity of some well-respected findings in the field.¹² For example, instead of directly influencing their friends, people may simply choose to form friendships with others who are already similar to them in lifestyle, socioeconomic status, and environments, which could collectively contribute to weight gain.

Ethical considerations

As awareness of social contagion’s influence grows, so do ethical concerns about its use in marketing, politics, and public health. Critics argue that engineering contagion through targeted ads or political messaging can manipulate choices without informed consent, raising questions about autonomy and transparency.¹² This debate echoes the concept of libertarian paternalism, introduced by Thaler and Sunstein, which suggests institutions can steer behavior through nudges while preserving freedom of choice. However, opponents contend that even subtle nudges exploit psychological biases and may undermine true autonomy.¹³

A classic example of this controversy is the 2014 Facebook emotional contagion experiment, where researchers manipulated the news feeds of 700,000 users without their knowledge to assess the spread of positive and negative emotions. This raised serious concerns about user autonomy, informed consent, and the manipulation of emotions for research purposes.¹⁴

Simple vs. complex contagion

Some argue that earlier models describing social contagion don’t accurately capture the complexity of human behavior. Originally, the theory assumed that each exposure to a particular behavior or idea independently increases the chance of adoption. However, real-world data often show more nuanced patterns: repeated exposure can sometimes inhibit rather than promote adoption, and network structure can alter the spread. This has led to the development of more sophisticated models, such as complex contagion (where multiple exposures are necessary to drive adoption). For example, repeated exposure to a new behavior can sometimes encourage adoption, but in other cases may cause resistance or fatigue, as has been observed in response to certain public health messages.¹⁷ Researchers continue to debate which models best capture real-world dynamics and how factors like novelty, information overload, and cognitive constraints shape contagion processes.³

COVID-19 vaccine hesitancy

A 2023 study explored how social contagion theory can help explain the spread of vaccine hesitancy during the COVID-19 pandemic in the United States. Researchers conducted a literature review to examine the relationship between social contagion, misinformation, and vaccine attitudes within social networks.⁶

The study found that misinformation about COVID-19 vaccines spread rapidly through social media and personal networks, influencing individual decisions about vaccination. Social contagion theory posits that people tend to adopt the behaviors and attitudes of those in their social circles. In this case, exposure to vaccine-hesitant or skeptical attitudes (whether through friends, family, or online communities) increased the likelihood that an individual would also become hesitant or refuse vaccination.

The researchers concluded that understanding the social contagion of vaccine hesitancy is crucial for public health interventions. By mapping how attitudes and behaviors spread through networks, public health officials can better target their messaging and interventions to disrupt the transmission of misinformation and promote positive health behaviors.

Viral dance challenges on TikTok

Do you remember the endless TikTok scrolls, YouTube binges, or internet rabbit holes that kept us entertained during the pandemic? While some of us were testing our sourdough starters or keeping up with celebrity life during quarantining, others stayed busy by learning all the trending TikTok dances, bringing moments of levity and fun in a challenging time. 

These seemingly lighthearted moments are actually driven by deep psychological mechanisms, such as peer influence, imitation, and algorithmic amplification. A 2021 study titled “Will You Dance To The Challenge? Predicting User Participation of TikTok Challenges” by Ng et al. investigated how social contagion drives participation in viral TikTok dance challenges.¹⁶ The researchers collected data from over 10,000 videos and 1,300 users, focusing on 12 trending challenges featured on TikTok’s “For You” page during the COVID-19 lockdown.

These researchers found that when an influential creator posts a challenge, their followers are more likely to replicate the routine and share their own videos. As more users join in, the trend gains momentum, appearing more frequently on the “For You” page and leading to even wider participation. The study identified several key mechanisms behind this process. First, imitation plays a role, as users are motivated to join when they see friends or influencers participating. Second, social proof contributes to the trend's appeal: as more people participate in a challenge, it becomes increasingly attractive to others, further encouraging imitation. Finally, algorithmic amplification by TikTok’s recommendation system boosts the visibility of trending challenges, accelerating their spread across the platform. Thus, these viral challenges demonstrate how behaviors can rapidly diffuse through digital networks and shape pop culture through social contagion mechanisms. 

Social Learning Theory

Social learning theory is a psychological framework developed by Albert Bandura that concerns how people learn through imitating others. This article explores the mechanisms required for social learning, such as attention and motivation. It also offers a detailed overview of the theory’s impact on psychological science, highlighting the importance of active engagement in learning and introducing key concepts like self-efficacy.

Nudges

This article on nudges explains how subtle changes in choice architecture-such as reordering menu items-can predictably influence people’s decisions. Just like social contagion, nudges can leverage social influence and peer behaviors to amplify their effects.

1. Christakis, N. A., & Fowler, J. H. (2013). Social contagion theory: Examining dynamic social networks and human behavior. Statistics in Medicine, 32(4), 556–577. https://doi.org/10.1002/sim.5408
2. Le Bon, G. (1895). The crowd: A study of the popular mind. London: T. Fisher Unwin. Centola, D., & Macy, M. (2007). Complex contagions and the weakness of long ties. American Journal of Sociology, 113(3), 702–734. https://doi.org/10.1086/521848
3. Ibid.
4. Blumer, H. (1951). Collective behavior. In A. M. Lee (Ed.), Principles of sociology (pp. 167–222). New York: Barnes & Noble.
5. Freud, S. (1921). Group psychology and the analysis of the ego. London: Hogarth Press. Canadian Public Health Association. (2017). Three degrees of social influence: The catchy idea of social contagion in public health.
6. Konstantinou, P., et al. (2021). Transmission of vaccination attitudes and uptake based on social contagion theory: A scoping review. Vaccines, 9(6), 607. https://doi.org/10.3390/vaccines9060607
7. Aral, S., & Nicolaides, C. (2017). Exercise contagion in a global social network. Nature Communications, 8, Article 14753. https://doi.org/10.1038/ncomms14753
8. Oxford Academic. (2025). Social media and the spread of misinformation. Health Promotion International, 40(2).
9. Del Vicario, M., Bessi, A., Zollo, F., Petroni, F., Scala, A., Caldarelli, G., ... & Quattrociocchi, W. (2016). The spreading of misinformation online. Proceedings of the National Academy of Sciences, 113(3), 554-559. https://doi.org/10.1073/pnas.1517441113
10. HRD Connect. (2023). The Ripple Effect: Understanding organizational behavior contagion to cultivate culture at scale.12. Ross, L. (2023). Emotional and social contagion: Three ways it impacts your organisational culture.
11. Shalizi, C. R., & Thomas, A. C. (2011). Homophily and contagion are generically confounded in observational social network studies. Sociological Methods & Research, 40(2), 211-239. https://doi.org/10.1177/0049124111404820
12. Sunstein, C. R. (2016). The ethics of influence: Government in the age of behavioral science. Cambridge University Press.
13. Hausman, D. M., & Welch, B. (2010). Debate: To nudge or not to nudge. Journal of Political Philosophy, 18(1), 123-136. https://doi.org/10.1111/j.1467-9760.2009.00301.x
14. Kramer, A. D. I., Guillory, J. E., & Hancock, J. T. (2014). Experimental evidence of massive-scale emotional contagion through social networks. Proceedings of the National Academy of Sciences, 111(24), 8788-8790. https://doi.org/10.1073/pnas.1320040111
15. Konstantinou, P., et al. (2021). Transmission of vaccination attitudes and uptake based on social contagion theory: A scoping review. Vaccines, 9(6), 607. https://doi.org/10.3390/vaccines9060607
16. Ng, K. H., et al. (2021). Will You Dance To The Challenge? Predicting User Participation of TikTok Challenges. Proceedings of the Web Conference 2021, 1160-1170. https://doi.org/10.1145/3442381.3450052
17. Chou, W.-Y. S., Gaysynsky, A., Vanderpool, R. C., & Viswanath, K. (2022). The role of fatigue in a campus COVID-19 safety behaviors study. BMC Public Health, 22, 1785. https://doi.org/10.1186/s12889-022-13989-6
18. Le Bon, G. (1896). The crowd: A study of the popular mind. Media Studies Press.https://www.mediastudies.press/pub/emet-le-bon-crowd/release/2
19. Freud, S. (1922). Group psychology and the analysis of the ego (J. Strachey, Trans.). International Psycho-Analytical Press. (Original work published 1921) https://www.gutenberg.org/ebooks/35877
20. EBSCO Research Starters. (n.d.). Collective behavior: Contagion theory. EBSCOhost. Retrieved June 5, 2025, fromhttps://www.ebsco.com/research-starters/psychology/collective-behavior-contagion-theory