Sharing painful experiences can create feelings of solidarity within a group, acting as a kind of "social glue" that fosters cohesion, Australian researchers say.

Despite being an unpleasant experience, a painful episode experienced by a group together can have social consequences of a positive nature, psychological researchers at the University of New South Wales say.

"Our findings show that pain is a particularly powerful ingredient in producing bonding and cooperation between those who share painful experiences," says research leader Brock Bastian. "The findings shed light on why camaraderie may develop between soldiers or others who share difficult and painful experiences."

Bastian and his colleagues conducted a series of experiments on volunteer undergraduates at the university to analyze links between pain and subsequent social bonding.

In one, 54 students were randomly assigned to two versions of a task involving submerging their hands in a bucket full of water to retrieve and remove a number of metal balls lying at its bottom.

For one group the water in the bucket was painfully cold; for the other the water was at room temperature.

After some similar tasks that were also either painful or not, depending on which group they were in, the participants were asked to rate statements describing their group, such as "I feel part of this group of participants," of "I feel a sense of loyalty to the other participants."

Students who were given the pain-inducing tasks expressed a greater level of bonding with their group than those performing the pain-free forms of the same task, the researchers reported.

Since the groups were put together by random assignment, they possessed no other kind of shared identity apart from their task-related experiences, they said.

"This finding puts the 'pain as social glue' hypothesis to a rigorous test, highlighting that people not only feel closer to others, but are willing to risk their own outcomes to benefit the group," says Bastian.

Pain fosters cooperation, the researchers suggest, because it captures a person's attention and focuses their awareness, and if they are in a group experiencing it together then their fellow sufferers become important to them.

"Sharing pain therefore is an especially powerful form of shared experience," the researchers report, because it "promotes bonding, solidarity, and, ultimately, cooperation."

The findings may provide insights into the many practices around the world -- social, religious, even sexual -- in which some component of pain is involved, they say.

"Pain, it seems, has the capacity to act as social glue, building cooperation within novel social collectives," they conclude.