As you may have discovered during a relentless tickle attack, it’s really tough not to laugh, even when you hate it. According to Dr. Alan J. Fridlund, an expert on nonverbal communication and an Associate Professor in the Department of Psychological and Brain Sciences at the University of California, Santa Barbara, that’s because laughing is a reflexive, often uncontrollable response to being tickled.
“The laughter and grimacing doesn’t mean ticklees are enjoying themselves,” he says. “You can see the evidence during ‘tickle torture’—the grimacing gets tighter and the laughter gets even more frantic, but ticklees may be yelling STOP. The tickling can get so intense as to induce a temporary state of cataplexy, or muscle paralysis, that precludes the tickle-torture victim from fighting off the perpetrator, who may misinterpret what’s going on as still fun.”
So why does this happen? “Unfortunately, no one on earth can totally explain it,” says Nicholas Christenfeld, a professor of Psychology at the University of California, San Diego. Christenfeld says there are many theories about what tickling is—and why it is—but none has been scientifically proven. Here are some of the possible explanations:
Theory One: Bonding
Tickling may be a way to forge relationships between family members and friends, which is why it’s often one of the first forms of communication between babies and their caregivers. In a sense, tickling is our first conversation—a way to talk to someone despite one party being unable to communicate verbally.
Theory Two: Guarding
Tickling could be how we learn to protect the most vulnerable parts of our body. “Observers have long noted that we are ticklish in many of our most vulnerable places, like our necks, under our arms, our abdomens, and the soles of our feet,” Fridlund says. “We have a tendency to recoil when others approach these areas.” Fridlund explains that when we’re socialized in infancy to play “tickle games,” we’re in fact being taught not to recoil but to take it, and the tension-and-release results in laughter. Children learn to protect those parts during tickle fights, a relatively safe activity.
Theory Three: Signaling
Christenfeld explains that some believe tickling is a way to signal a play-fight, like lion cubs rolling around outside the den. “If passers by didn’t know they were playing, they’d think the cubs were trying to kill each other. You can make the argument that our ancestral humans did the same thing.”
Theory Four: Protecting
“Knismesis” is a phenomenon involving low levels of stimulation to sensitive parts of the body. The evolutionary purpose of this form of tickling is to detect an insect or parasite crawling up your armpit, forcing you to reflexively swat it away before it digs in. Knismesis produces a similar response in many different kinds of animals, including horses and sharks.
As for the when tickling is appropriate, context is everything. Nobody likes a stranger tickling them, for example: For adults, the category of people they like ticking them typically ranges from zero to one, with zero for those who absolutely hate being tickled by anyone under any circumstances, and one for people who actually like being tickled by their mate. In the latter case, of course, it’s often sexual: “It’s intimate, people are touching you,” says Christenfeld. “Also, it involves a lack of control—tickling forces you to respond and often renders you helpless. It’s only under very special circumstances that people like that.” One thing’s for sure: you can’t tickle yourself. This is for the same reason you can’t say “boo!” to yourself and be startled: When you try to tickle yourself, the cerebellum predicts the sensation and cancels the response to it.
So why are some people more ticklish than others? According to Fridlund, no one knows for sure. “More anxious people may be more ticklish, even though they may enjoy being tickled less. The social context in which the tickling occurs, and the nature of the relationship between tickler and ticklee, are the prime determinants of how tickling is taken.” The main takeaway here is that, unless your name is Elmo, you should never tickle anyone unless it’s requested.