Why armpits and soles tickle the most: researchers mapped 448 bodies to find out

The palm is among the most densely innervated parts of the body, yet no amount of touching it produces a ticklish sensation. The armpit, by contrast, has far fewer nerve endings — but the lightest brush can send someone into fits of laughter.

Why only certain spots are ticklish is a question that dates back to Aristotle. A new study that mapped the bodies of 448 participants found the answer lies not in nerve density or skin thickness, but in how rarely a given area is touched by others — the less contact a spot receives, the more ticklish it tends to be.

The findings were published in Nature Human Behaviour by a research team led by Drs. Xiong Ziliang and Konstantina Kilteni of the Donders Institute at Radboud University in the Netherlands.

The research team gave participants two body outline drawings — front and back — divided into a combined 91,617 regions, and asked them to color in their responses.

Participants shaded areas where they felt ticklish when touched by a family member or friend, coloring more heavily over spots they found especially ticklish. Using the same method, they also marked areas that were painful, sensitive to light touch, pleasurable or frequently touched by their own hands.

The exercise allowed the team to test five competing hypotheses: that ticklishness correlates with nerve density, skin thickness, proximity to vital organs, erogenous zones or areas rarely touched in daily life.

The results ruled out all four hypotheses related to nerve density, skin thickness and similar physical factors.

The team then overlaid three separate touch maps — areas participants said they touched themselves, areas touched by family and friends, and areas touched by romantic partners — against the ticklishness map.

A clear pattern emerged: the less contact a body part received, the more ticklish it was. Areas with dense nerve endings and those associated with pleasurable touch were, if anything, less ticklish.

The research team explained that hands are not ticklish while armpits are because hands are in near-constant contact with objects and surfaces throughout the day, whereas armpits are rarely touched by others — making them highly reactive to unexpected contact.

All three countries colored in the same spots: armpits, abdomen and soles

The ticklish zones participants identified were consistent across nationalities. The neck, armpits, abdomen and soles of the feet ranked as the most ticklish areas in all three countries surveyed. When the person doing the tickling was a romantic partner, the groin and inner thighs were added to the list.

A survey conducted as part of the study found that 98.4 percent of respondents said they had been tickled at least once in their lives, while 95.8 percent said they had tickled someone else.

However, the experience differed sharply depending on which side of the tickling a person was on.

Among those who had tickled others, 67.6 percent said they found it enjoyable as children and 62.3 percent as adults; fewer than 1 percent said they found it unpleasant. Among those on the receiving end, only 41.8 percent said they enjoyed being tickled as children — less than half — while 26.3 percent said they found it unpleasant.

When asked whether people generally enjoy being tickled regardless of age, 27.2 percent of respondents agreed and 27.9 percent disagreed — a near-even split. While 76.8 percent agreed that tickling is done to make someone laugh, 47.3 percent said that laughter does not necessarily reflect genuine enjoyment.

Ticklishness is not unique to humans. Chimpanzees and bonobos also display the behavior, using their hands and fingers to tickle each other's armpits, soles, abdomen and neck and producing laughter-like vocalizations. As with humans, they tickle more frequently with those they are close to, and the behavior decreases with age.

The research team acknowledged that the study covered only laughter-inducing ticklishness and excluded lighter sensations such as those produced by a feather. They also noted that while the research could not determine whether ticklishness is innate, it confirmed that the experience is shaped over a lifetime by how much and how often different parts of the body are touched.

DOI: 10.1038/s41562-026-02535-z

Xiong, Z., Kilteni, K. Human ticklishness is a widespread, culturally shared and bodily organized sensory experience. Nat Hum Behav (2026).