Mice housed in the same room as one another can pass certain types of pain to each other through smell.

Exposure to inflammatory molecules or withdrawal from drugs or alcohol can cause hyperalgesia, a painful hypersensitivity to touch, heat or chemical irritants. Andrey Ryabinin and his colleagues at Oregon Health and Science University in Portland found that when mice were subjected to these pain-inducing treatments, untreated mice in the same room also acquired hyperalgesia. Moreover, mice in a separate room began displaying this pain sensitivity after exposure to bedding used by the hyperalgesic animals in the first room. The authors conclude that the pain is transmitted by an olfactory cue.

Social transfer of pain could play a part in chronic pain in humans, especially in cases without apparent physiological cause, the authors suggest.

Sci. Adv. 2, e1600855 (2016)