Laughter must really be the best medicine, or at least a pain reliever, according to a recent study.

An evolutionary psychologist at Oxford, Robin Dunbar, said the muscles involved in the physical act of laughing triggers an increase in endorphin, a brain chemical that makes one feel good even after suffering physical pain.

Dunbar's findings are consistent with previous studies that reveal laughing does well for the body.

"Laughter is very weird stuff, actually," Dr. Dunbar said. "That's why we got interested in it."

His findings were published in the Proceedings of the Royal Society B: Biological Sciences.

In his findings, Dr. Dunbar discussed social laughter, which breeds comfort and closeness in a group.

In five sets of studies in the laboratory and one field study at comedy performances, Dr. Dunbar and colleagues tested resistance to pain both before and after bouts of social laughter. The pain in this study was a result of freezing wine sleeve slipped over a forearm, an ever tightening blood pressure cuff or an excruciating ski exercise.

Dr. Dunbar zeroed in on the act of laughing as pain resistance management tool. He ruled out the likelihood that the pain resistance measured was the result of a general sense of well being. He also provided an answer to the ageless question on whether people laugh because of feeling giddy or people giddy because of laughing.

"The causal sequence is laughter triggers endorphin activation," Dr. Dunbar said. However, there are still many possibilities as to what actually triggers laughter.

To test the relationship of social laughter to pain resistance, Dr. Dunbar did a series of six experiments. In five, participants watched excerpts of comedy videos, neutral videos or videos meant to promote good feeling but not laughter.

Among the comedy videos were excerpts from generally acknowledged as hilarious TV cartoons and sitcoms, like "The Simpsons," "Friends" and "South Park." Standup comedian performances were included, too. Neutral videos included "Barking Mad," a documentary on pet training, and a golfing program. The positive but 'unfunny' videos included excerpts from shows about nature, such as the "Jungles" episode of "Planet Earth."

In the lab experiments, the participants were tested before and after seeing different combinations of videos.

The results showed that laughing increased pain resistance, whereas simple good feeling in a group setting did not.

Endorphin levels are not easy to test, as these are brain chemicals that do not circulate the body, making it impossible to spot in a blood test. This is why Dr. Dunbar used measurable pain resistance as an indicator of endorphin levels.

Other activities that produce endorphins are dancing and singing, both social activities in the same general category under which social laughter also falls. Dr. Dunbar thinks social laughter may have a relation to human evolution.

"Laughter is an early mechanism to bond social groups," he said. "Primates use it."