Source: JESSICA TICOZZELLI: Pexels

The word contagious rightly conjures thoughts of bacterial or viral infection spreading from one person to another. The idea that psychological factors can be contagious is not as well-known. Psychological states, including stress, can be spread from one person to another, similar to traditional infectious diseases.

Large datasets about human health and behavior have allowed scientists to study psychological interconnectedness. Analysis of social networks—both in real life and online—has revealed that characteristics ranging from happiness to smoking to obesity can spread from one person to another (and another). This work corroborates your parents’ warnings about peer pressure: we are strongly influenced by the behaviors of those around us.

The feelings and physiology of stress show the same contagion. This pattern is obvious to anyone who’s observed a struggling public speaker. The audience may feel as stressed as the speaker. In human stress research, one way to elicit a stress response is to ask people to speak in public. Surveys often place public speaking near the top of the list of people’s greatest fears. It is also effective at eliciting a physiological stress response in the form of increased heart rate, blood pressure, and cortisol.

In our stress lab, we ask people to give a speech in front of research assistants trained to passively observe the speaker, showing no reaction. This situation of passive social observation is remarkably effective at eliciting a stress response in the speaker. The lack of reaction on the part of the research assistants seems somehow worse than negative feedback.

After conducting this research for many years, my colleague and I observed that the speech seemed effective at eliciting a stress response in us and in the speakers. Of course, these were just anecdotal observations, but it led us to design a research study to test whether we could observe physiological changes in the observers as well as in the speakers.

To assess such responses, we collected saliva samples to measure the stress hormone cortisol. What we found surprised us: when speakers showed high cortisol responses, the observers also showed high responses. We described this matching as "physiological resonance." It was as if the stress system in the speaker had a direct impact on the stress system in the observers.

Maybe this shouldn’t have surprised us, given the contagion of all sorts of feelings and behaviors observed in people over the years. The question that remains unanswered is: What aspects of the speaker’s behavior cue the observer to produce a stress response? Research has focused on the speakers’ voices and facial expressions, but no simple description has provided a strong link between observed behavior in one person and physiological responses in another.

We process a variety of social cues when we interact with others. This allows us to assess the well-being of our friends and neighbors. This also allows us the ability to detect potential threats in the environment. If your neighbor shows signs of stress, you’d best pay attention. What impacts your neighbor is likely to affect you as well. Such sensing is a holdover from our evolutionary history. There are many examples of other animals picking up on stress cues from one another. Quick detection of stress from our neighbor could give us a head start on avoiding the worst consequences of stress.

The contagion of stress may occur in many settings, impacting family and work dynamics. This contagion demonstrates our interconnectedness, even at a physiological level. It also represents a public health challenge not just for those under stress but also for other people in their vicinity.