Is Pain Contagious?

A strong friendship or deep personal connection to someone else requires a healthy dose of empathy and intuition to detect when they may be suffering. Usually, though, we think of that as an emotional thing, rather than a physical one — whether or not physical pain is contagious might not even occur to us. But a group of scientists recently set out to investigate whether or not pain is transferrable socially, and it turns out that in mice, it might be. If the study results can be replicated in humans, it may go some way in explaining how things like fibromyalgia actually occurs.

The research was led by Andrey Ryabinin from Oregon Health and Science University in Oregon and published in Science Advances. Ryabinin and his team caged mice one to two meters apart in such a way that they were unable to see each other. Some mice were then subject either to alcohol or heroin withdrawal, or had a chemical irritant injected into their paws. In order to test their hypersensitivity, the scientists tickled the mice's feet with fine hair, measured how quickly the mice licked their paws to clean away the irritant, or dipped the ends of their tails in warm water to see how quickly they withdrew them. Ryabinin's team found that the mice subjected to pain were just as aware of it as the ones who weren't subjected to anything at all (termed "bystander mice").

There were, however, degrees of awareness. Said Ryabinin according to New Scientist, “When the pain was caused by alcohol or heroin withdrawal, the scores for the bystanders completely matched those of the experimental animals." When the experimental mice felt pain from an irritant, the hypersensitivity scores in the bystanders was about halved, but were still higher than the controls. Commenting on the findings, Ryabinin said, “Pain can develop from social cues. We’ve shown for the first time that you don’t need an injury or inflammation to develop a pain state."

In the mice, the "contagious" pain is thought to have spread by smell (that is, the mice in pain emitted smells that gave off cues for hypersensitivity, which the bystander mice picked up on)— but we don't know whether the same is true of humans yet. Indeed, previous research has found that for humans, it's seeing another person in pain that might make us wince. Research from 2013 out of Monash University examining "somatic contagion" found that witnessing someone else in pain triggers a pain response in some watchers; however, the pain response experienced by the watcher often causes them to focus on their own pain, rather than that experienced by the other person. About one in three people are thought to have this sort of response. So, even though the pain is "contagious," it doesn't necessarily mean that we're sympathetic to what someone else is experiencing.

Whilst the current study is interesting, it will be difficult to ascertain whether or not people behave in a similar way; more research is clearly needed, but the ethical guidelines for studying pain are quite complex. But if you find yourself suddenly feeling a physical pain after being near someone who has been similarly hurt? Well, this might go some ways toward explaining why.

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