Why Are We Ticklish?

The phenomenon of ticklishness has puzzled scientists and philosophers for decades. From social bonding to survival, researchers have offered a wide range of theories to explain this peculiar bodily quirk.

Opposing Theories

Charles Darwin argued that the mechanism behind ticklishness is similar to the way we laugh in response to a funny joke. In both cases, he contended, one must be “light” state of mind in order to respond with laughter.

Sir Francis Bacon made an opposing claim when he said on the subject of tickling, “...[W]e see that men even in a grieved state of mind, yet cannot sometimes forbear laughing." The opposing theories of Darwin and Bacon reflect some of the contemporary conflicts that exist in research on tickling today.

Tickling as Social Bonding

Tickling may function as a form of social bonding, especially for a parent and child. University of Maryland neuroscientist Robert Provine, who considers ticklishness to be “one of the broadest and deepest subjects in science,” says that the laughter response to being tickled is activated within the first few months of life and that tickling as a form of play helps newborns connect with parents. 

It's also possible that the horseplay and other games involving tickling help us hone our ability to defend ourselves — a kind of casual combat training. This view is supported by the fact that the regions of the body that happen to be most ticklish, such as the armpits, ribs, and inner thighs, are also areas that are particularly vulnerable to attack.

Tickling as a Reflex

Research into the physical response to tickling has led to conclusions that conflict with the social bonding hypothesis. The social bonding hypothesis really starts to fall apart when one considers those who find the experience of being tickled unpleasant. A study conducted by psychologists at the University of California in San Diego found that subjects can experience an equal degree of ticklishness regardless of whether they believe they are being tickled by a machine or a human.

From these findings, the authors drew the conclusion that being ticklish is more likely a reflex than anything else.

If ticklishness is a reflex, why can’t we tickle ourselves? Even Aristotle asked himself this question. Neuroscientists at University College London used brain mapping to study the impossibility of self-tickling. They determined that the region of the brain responsible for coordinating movements, known as the cerebellum, can read your intentions and even predict exactly where on the body an attempt to self-tickle will occur. This mental process prevents out the intended "tickle" effect.

Types of Ticklishness

Just as there is a wide variation to where and the degree in which a person is ticklish, there is more than one type of tickle. Knismesis is the light, gentle tickling felt when someone runs a feather across the surface of the skin. It does not typically induce laughter and can be described as irritating and slightly itchy. Conversely, gargalesis is a more intense sensation triggered by aggressive tickling and usually provokes audible laughter and squirming. Gargalesis is the type of tickling used for play and other social interactions. Scientists speculate that each type of tickle produces markedly different sensations because the signals are sent through separate nerve pathways.

Ticklish Animals

Humans are not the only animals with a tickle response. Experiments in rats have shown that tickling rodents can trigger inaudible vocalizations that are akin to laughter. A closer measurement of their brain activity using electrodes even revealed where the rats are most ticklish: along the belly and the bottoms of the feet.

However, the researchers found that the rats who were put in a stressful situation did not have the same response to being tickled, which suggests that Darwin's "light state of mind" theory might not be totally off base. For the human population, the explanation for the tickle response remains elusive, tickling away at our curiosity.