Laughter comes in two main types, scientists found.
Laughing with friends releases feel-good brain chemicals, which also relieve pain, new research indicates.
Until now, scientists haven't proven that like exercise and other activities, laughing causes a release of so-called endorphins.
"Very little research has been done into why we laugh and what role it plays in society," study researcher Robin Dunbar, of the University of Oxford, said in a statement. "We think that it is the bonding effects of the endorphin rush that explain why laughter plays such an important role in our social lives."
Chuckle it up
Dunbar and colleagues thought our guffaws might turn on the brain's endorphins, a long debated, but unproven idea. These pain-relieving chemicals are created in response to exercise, excitement, pain, spicy food, love and sexual orgasm, among other things.
In addition to giving us a "buzz," these endorphins raise our ability to ignore pain. So the researchers used the endorphins' pain relief to determine if laughter causes an endorphin release. They first tested participants for their pain threshold, then exposed them to either a control or a laugh-inducing test, and then tested pain levels again.
The tests included humorous videos (clips of the TV shows "Mr. Bean" and "Friends") and a live comedy show during the Edinburgh Fringe Festival. Because laughter is such a social activity (it's 30 times more likely to happen in a social context than when alone), the participants were tested both in groups and alone.
The lab-based pain tests included wrapping a participant's arm in a frozen wine-cooling sleeve or a blood-pressure cuff. The pain tests were administered until the patient said they couldn't take it anymore. At the live shows, the researchers tested pain by having participants squat against a wall until they collapsed.
Why laughter releases endorphins
Across all tests, the participants' ability to tolerate pain jumped after laughing. On average, watching about 15 minutes of comedy in a group increased pain threshold by 10 percent. Participants tested alone showed slightly smaller increases in their pain threshold.
"When laughter is elicited, pain thresholds are significantly increased, whereas when subjects watched something that does not naturally elicit laughter, pain thresholds do not change (and are often lower)," the authors write in the paper. "These results can best be explained by the action of endorphins released by laughter."
The researchers believe that the long series of exhalations that accompany true laughter cause physical exhaustion of the abdominal muscles and, in turn, trigger endorphin release. (Endorphin release is usually caused by physical activity, like exercise, or touch, like massage.)
The study was published today (Sept. 13) in the journal Proceedings of the Royal Society B: Biological Sciences.