My three young daughters like to watch pets doing silly things. Almost daily, they ask to see animal video clips on my phone and are quickly entertained. But once my 7-year-old lets out a belly laugh, the laughter floodgates are opened and her two sisters double over as well.
“Laughter is a social phenomenon,” says Sophie Scott, a neuroscientist at University College London who has studied laughter and other human reactions for more than two decades. Scott co-wrote a study showing how the brain responds to the sound of laughter by preparing one’s facial muscles to join in, laying the foundation for laughs to spread from person to person.
“Contagious laughter demonstrates affection and affiliation,” Scott says. “Even being in the presence of people you expect to be funny will prime laughter within you.”
It’s like yawning
Scientists have yet to definitively find a funny bone, but they are revealing nuances about the laugh impulse. Laughter’s positive psychological and physiological responses include lessening depression and anxiety symptoms, increasing feelings of relaxation, improving cardiovascular health, releasing endorphins that boost mood and even increasing tolerance for pain.
Laughing has also been shown to lower stress levels. “Cortisol is a stress hormone that laughter lowers,” says Scott, adding that anticipation of laughter also “drops your adrenaline” and the body’s heightened fight-or-flight response. “All of these things contribute to you feeling better when you’ve been laughing,” she says.
Because humans are wired to mirror one another, laughs spread around a room just like yawns, says Lauri Nummenmaa, a brain researcher and professor at Aalto University School of Science in Finland whose work appears in a recent special issue on laughter in the journal Royal Society.
“We simply copy the behavior and laughter of others,” Nummenmaa says. “Someone else’s act of laughing is first perceived when seen or heard, and this sensory information is then converted into the same area of the observers’ brain.”
Studies also indicate that laughter can strengthen relationship connections. This happens, in part, because people naturally want to be around those who make them feel good the way laughing does. “We crave the company of the individuals who can give us such feelings,” Nummenmaa says. “Laughter is kind of a molecular building block of friendship.”
Adds Scott: “You’re much more likely to catch a laugh from someone you know.”
Sending a play signal without words
Contagious laughter isn’t necessarily a phenomenon unique to humans. Great apes, for instance, have been documented behaving similarly.
“Laughter is a play signal in humans and many other animals,” says Disa Sauter, a social behavior professor at the University of Amsterdam. “It is used in rough-and-tumble play across species.”
The play-laughter connection is an important one. Certain sounds, or vocalizations, serve as important cues across the animal kingdom that playtime has begun.
“Vocal play signals frequently accompany other nonvocal behaviours, such as the play face in primates … or the play bow in dogs,” according to a 2021 study in the journal Bioacoustics. The cues help differentiate threatening actions from play fighting and wrestling.
Behavioral scientists also want to understand the role laughter takes among children playing together. “We need to understand how laughter is used by children to signal that rough-and-tumble play is just playing and not a real fight,” Nummenmaa says.
Malicious chuckles and laugh attacks
You can, of course, laugh alone, but the contagious nature of laughter means we’re more likely to laugh harder and longer in groups, as at a comedy club or in a movie theater.
Psychologist Robert Provine showed that “you’re 30 times more likely to laugh with other people than you are on your own,” Scott says. In his seminal book, “Laughter: A Scientific Investigation,” Provine wrote that the “contagious laugh response is immediate and involuntary, involving the most direct communication possible between people: brain to brain.”
Researchers are working to define different types of laughter and how humans adopt each one in various settings; think malicious laughter to signal authority, or nervous laughter to express uncertainty.
“Laughter has many subtle rules that make adults highly attuned to when it’s socially appropriate,” says Harry Witchel, a physiologist and neuroscientist at Brighton and Sussex Medical School in Brighton, England.
There are circumstances, he notes, when people laugh at something that is not humorous: “Laughter is regularly linked to joy, relief, tickling, sudden incongruity, social discomfort, dominance, humiliating another and many other causes.”
And there are other instances when the contagious nature of laughter becomes problematic.
In “Laughter,” Provine described “laugh epidemics” that have occurred throughout history, including “holy laughter” that cropped up in some churches. There was also the “plague of laughter” that befell numerous Central African schools starting in 1962: Contagious “laugh attacks” among several groups of students lasted several hours to many days and continued until two schools had to close for extended periods of time.
Scott has studied such events as well and was one of more than 40 researchers and academics who contributed to “Cracking the laugh code: laughter through the lens of biology, psychology and neuroscience,” a September 2022 issue of the journal Proceedings of the Royal Society B. Their work is part of a long-running scientific effort to analyze what makes humans chortle, guffaw, giggle, titter and more.
Although scientists have uncovered much about laughter’s health benefits and its contagious element, there remain many unknowns, including how contagious laughter is learned in the first place.
“Babies aren’t born doing this,” Scott says. “All we know is that people do learn to laugh contagiously eventually, but we don’t know how or when exactly it begins.”