Researchers discovered a genetic link between physical pain and social rejection.
Psychologists at the University of California in Los Angeles have discovered that the human body deals with emotional stress in exactly the same way that it reacts to physical pain - by releasing a natural painkiller.
Scientists believe their findings suggest that the experience felt by people is the same regardless of whether their body is injured.
The researchers measured levels of a gene used by the body to regulating the painkillers.
Researchers collected saliva samples from 122 participants to assess which form of the OPRM1 pain gene they had and then measured how they reacted to different senarios.
First, participants completed a survey that measured their own sensitivity to rejection. They were asked, for example, how much they agreed or disagreed with statements like "I am very sensitive to any signs that a person might not want to talk to me."
Then the emotions of 31 people among the group were tested when they were excluded during a virtual ball-tossing computer game.
Prof Naomi Eisenberger, the study co-author, said this overlap of physical and social pain makes perfect sense.
She said: "Because social connection is so important, feeling literally hurt by not having social connections may be an adaptive way to make sure we keep them.
"Over the course of evolution, the social attachment system, which ensures social connection, may have actually borrowed some of the mechanisms of the pain system to maintain social connections."
The same portion of the brain that is responsible for the response to physical pain became activated as a result of social rejection, suggesting that, to our brains, emotions really can "hurt."
Their study also indicates that a variation in the "pain gene" is related to how sensitive a person is to social rejection.
Prof Eisenberger said: "Individuals with the rare form of the pain gene, who were shown in previous work to be more sensitive to physical pain, also reported higher levels of rejection sensitivity and showed greater activity in social pain-related regions of the brain when they were excluded."
This is the first time that it has been proved that genes involved in physical pain are linked to mentally painful times like social rejection and breaking up with a lover, she said.
The findings back up a previous study by the University of Queensland that indicated that descriptions of the agony of rejection as like a knife being thrust into the heart are more than just metaphors.
Dr Geoff MacDonald said it is no coincidence that people across different cultures and languages use similar terms to describe physical pain and what it feels like to be rejected.