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Why do we dislike sitting next to strangers so much?

25 April 2024

We’ve all been there: We’re on the train and have made ourselves at home in one of two adjacent seats, the other being unoccupied. But then someone sits down next to us – and that makes us feel uncomfortable. Why is it that we tend to tense up when strangers get too physically close to us?


Researchers at Cornell University in the US have discovered that the physical proximity of strangers is a specific cause of stress. The psychologists asked commuters questions about their well-being and tested their saliva for stress hormones. The results showed that it really didn’t matter how full the compartment was overall; however, having a stranger sit down next to them would increase their stress level like nothing else. “Having a person in the seat next to us encroaches on the invisible safety zone that we claim for our own body,” explains Christian Müller from the Medical-Psychological Institute of TÜV NORD in Cologne.

In technical terms, this protected zone around us is called the peripersonal space. It is supposed to protect us from attacks and physical injury, and in all likelihood also from contagious diseases. “In this protected space, we only tolerate strangers if there’s a good reason for physical closeness to them,” says psychologist Christian Müller. Examples of such good reasons would include a medical check-up, a full lift, or a crowded underground train where everyone is forced to stand close together. “That’s why there’s this unwritten law that we don’t sit right next to a stranger when two adjacent seats are still available,” Mr. Müller explains.


From flight distance to proxemics

Swiss zoologist and zoo director Heini Hediger first described this safety zone in the 1930s. Mr. Hediger discovered that zebras, for example, always maintain a certain flight distance not just from potential attackers, but also from their own kind.

US anthropologist Edward T. Hall recognised that Homo sapiens behaves similarly. In the 1960s, Mr. Hall developed his own field of expertise: The psychology of human spatial behaviour, or “proxemics” for short. According to this theory, the degree of familiarity between two people is reflected in their physical proximity.


Differences between the strange and the familiar

As a matter of principle, we keep our distance from strangers for safety reasons: We need one to three metres to feel comfortable. Too far away for us to be able to touch each other, but close enough to potentially make eye contact. Close acquaintances are allowed to stand at arm’s length; friends, on the other hand, may get as close as fifty centimetres. Everything closer than that is reserved for our most intimate contacts.

If objects or “unauthorised” people invade these protection zones, certain nerve cells will trigger an evasive or defensive response. This is ensured by a system in our brain that unconsciously monitors the position of objects and living beings. The closer a stranger gets to us, the louder the nerve cells ring the alarm bells.


Mood-dependent protected areas

The size of the invisible safety bubble around us differs from person to person but is just as dependent on our form on the day or other conditions. For example, tools or a prosthesis can make the body bigger and thus also expand our peripersonal space.

The protection zone also grows or shrinks depending on our mood or environment. In unpleasant or frightening situations, our personal protective space increases in size. This effect can even occur when we witness an aggressive conversation between others. Overall, the protection zone grows when we feel vulnerable: For example, in the last trimester of pregnancy, in old age, but also when we are very tired or exhausted.


Invasive alpha males

Men with a higher social status, on the other hand, like to demonstrate their dominance by forcing their way into other people’s personal protective space. This is a phenomenon that is clearly observable in the case of former US President Donald Trump, for example. He was notorious for giving other political dignitaries a pat on the back and, when shaking hands for the cameras, liked to draw the other’s person’s hand towards him, only releasing it again after what felt like an eternity.

In general, our personality has an influence on our comfort zone. Suspicious personalities, for example, need a greater minimum distance, as do people suffering from schizophrenia: They are also less able to tolerate someone overstepping their boundaries.


Public transport as an endurance test

Differences of this kind are particularly visible on public transport. “When things get too crowded, people create non-verbal distance in other ways,” explains Christian Müller from TÜV NORD. We cross our arms, turn our bodies away and avoid eye contact. This is how we subconsciously signal that we have no interest in social interaction. “For some, proximity is so hard to bear that they prefer to stand,” says psychologist Christian Müller. “This lets them take evasive action to restore the necessary minimum distance.”

It’s for this reason that a journey by bus or train always offers enough material for a psychological field study. The psychologist’s suggestion is this: “When you’re sitting in a crowded train, watch the body language of your fellow passengers – discreetly, of course. If you’re feeling uncomfortable, you'll notice that you’re not alone.”