Pain could be contagious, a groundbreaking new study claims. Lab mice were put through a series of tests which should not have been painful – ticklish at the most. But the rodents reacted as if their feet were burning. The experiments by researchers in Portland, Oregon, suggested the mice caught this heightened sensitivity from other mice who were primed to feel pain. Both groups of mice were in the same room, in cages approximately 1.5 metres apart from each other – but they could not see each other. The scientists believe they picked it up through smell. If true, this could explain some mysterious illnesses, including fibromyalgia – the feeling of pain without a logical medical reason for it. “We’ve shown for the first time that you don’t need an injury or inflammation to develop a pain state,” lead researcher Andrey Ryabinin, a neuroscientist at Oregon Health & Science University, said. “Pain can develop simply because of social cues.” Even Ryabinin was surprised by the result of the study – which was not the point of his investigation. Working with a team of graduate students, he was exploring alcohol addiction, and whether people in withdrawal feel pain more acutely. Decades of research and anecdotal evidence suggest this is true for humans. But no study has found any difference in pain sensitivity between mice in withdrawal and healthy mice – both seem to find a light touch excruciating. Ryabinin wanted to tackle the issue once more, and came up against the same problem. They then decided to explore it further. They created three groups – one in withdrawal from alcohol or drugs, then two groups of un-afflicted mice. One of these healthy groups lived in the same room as the drugged mice, the other lived separately. The team discovered the healthy mice living separately had normal sensitivity to pain. On the other hand, the healthy mice living with the drugged mice found even the faintest stroke painful. Finally, Ryabinin took some bedding from the drugged mice and placed it in the room of the isolated healthy mice – who then began to feel pain more acutely. Writing in a paper published in Science Advances on Wednesday, the team concluded smell to be the clearest cause of infection. The controversial finding has divided neuroscientists. If true, however, it could bring into question years of studies involving lab mice and pain, which likely did not account for the possibility of pain contagion.