Every family seems to have one: the person who starts giggling before anyone even touches them. And then there's the relative who sits stone-faced while you try every ticklish spot you know. Why does tickling turn some of us into puddles of laughter while others hardly react?
Here's the honest answer. Scientists don't fully know. Studies have found that it's unclear why certain people find some areas more ticklish than others, and men and women don't differ significantly in how ticklish they are. What researchers do know is that tickling depends heavily on surprise, on how you feel about the person doing it, and on your own expectations. That helps explain why the same tickle can feel hilarious one moment and annoying the next.
Two Kinds of Tickle
In 1897, two psychologists described two different kinds of tickle. The first, called knismesis, is the light, itchy feeling you get when something brushes across your skin, like a crawling insect. It usually doesn't make you laugh. Many animals feel it too. It's why a dog's back leg kicks when you scratch the right spot, and why a horse twitches its skin when a fly lands.
The second kind, gargalesis, is the laugh-out-loud tickle caused by firmer pressure in sensitive places. This type is thought to be mostly limited to humans and other primates, though some research suggests rats can be tickled this way too.
Why You Can't Tickle Yourself
Try tickling your own ribs. Nothing much happens, right? Charles Darwin noticed this long ago. He reasoned that tickling only works when the person being tickled doesn't know exactly where the touch will land.
In 1998, researchers used brain scans to study this. When people controlled a 'tickling robot' with a joystick, they couldn't make themselves laugh. Scientists think a part of the brain called the cerebellum predicts exactly what your own movements will feel like, and the brain then dials down the sensation. No surprise, no tickle.
Mood, Trust, and Anticipation
Darwin also noticed that a stranger tickling a child out of the blue usually gets withdrawal, not laughter. Tickling seems to work best when people feel comfortable with each other. That's one reason psychologists see it as a bonding activity between parents and children.
Expectation matters too. Some evidence suggests that ticklish laughter is a nervous reaction that can be triggered in advance. Very ticklish people often start laughing before they're actually touched.
And here's a surprise: lots of people don't actually like being tickled. In one survey of 84 college students, only 32 percent said they enjoyed it, while 36 percent said they didn't. Some who said they disliked it actually smiled more during tickling than those who enjoyed it.
The Most Ticklish Spots
Oddly, the most touch-sensitive parts of the body aren't always the most ticklish. Your palm is far more sensitive than your foot, yet most people find the soles of their feet the most ticklish. Other common spots, in decreasing order, are the armpits, the neck, under the chin, and the ribs.
One old theory, proposed in 1924, says our most ticklish places are also the body's most vulnerable spots in a fight. Tickling might encourage us to protect them. A psychiatrist later noted that ticklish spots line up with the body's protective reflexes.
So if you're one of the lucky few who can't be tickled, or one of the many who can't stop laughing, you're in good company. Even some of history's greatest minds couldn't quite explain it.
