There are few things more delightful in life than a giddy, runaway laugh shared with a friend. When the mood strikes, chuckles can become contagious. But sometimes these bouts of hilarity bubble up at just the wrong moment, when social mores call for solemnity and a straight face. Anyone who has found themselves giggling during a funeral, for example, knows how difficult it can be to tone down their tittering.
Recently, a research team at the University of Göttingen decided to investigate what strategies humans can use to keep our laughter under wraps when situations demand seriousness. Some approaches work better than others, they found, but everything works less well when other people around us are guffawing. They published their results in Communications Psychology.
“Hearing another person laugh made it much harder to control laughter,” said co-author Anne Schacht, a Göttingen University psychologist, in a statement. “This just goes to show how strongly our emotional reactions are affected by the presence of others and how deeply humans are social beings.”
Read more: “Why Is That Funny?”
The subject of laughter regulation has gotten very little scientific attention, Schacht and her colleagues note, though plenty of research has addressed other types of emotional management, including both negative emotional states such as anger and sadness and positive emotions such as happiness and pride.
To fill this gap, the scientists ran three separate experiments with a total of 121 study participants. The volunteers were asked to listen to 100 jokes read by two men and two women—the readers were asked to recite the jokes in an amused and enthusiastic tone, but not to laugh—and to rely one of three approaches to keep a straight face: distracting themselves with a large busy illustration in which objects were hidden, focusing on keeping their facial expressions under control, and reinterpreting the jokes so that they felt un-funny.
To measure how well these strategies worked, the scientists used a technology called facial electromyography to record tiny muscle movements involved in smiling and laughter invisible to the naked eye. They also created a smile index to quantify combined activity from certain facial muscles. Laughter in particular involves muscles around the mouth, eye, and brow—including the zygomatic major, the orbicularis oculi, and the corrugator supercilii. To see how the volunteers felt about the jokes, they asked them to rate their funniness on a scale of 1 to 5.
In all three experiments, the jokes were the same, but the conditions were a little bit different. In the first experiment, the participants were asked to either reappraise the jokes or control their facial muscles. In the second, they were told to distract themselves with the illustration. In the third, they were asked to use self-suppression exclusively. In the first two, the participants were alone, but in the third, the scientists fed in video laugh tracks.
What the scientists found is that distraction and suppression do the best job of quieting the funny facial muscles, while rethinking the jokes mainly made the participants feel differently about how humorous they were. Suppression also worked less well with the best of the jokes, and did not affect funniness ratings.
But the funniest if least surprising finding was that listening to a laugh track made the jokes feel more hilarious and made it harder for participants to control their own amusement.
All of which is to say, laughter really is contagious. 
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