Researchers at Radboud University have identified global "hotspots" for ticklishness, including the armpits and foot soles. The study indicates these reactions are an evolutionary trait shared with great apes.
Armpits, soles, and the universal map of sensitivity
Radboud University researchers recruited nearly 450 people from Greece, China, and the Netherlands to map bodily sensitivity. According to the report , 71 per cent of these participants identified as moderately to very ticklish, with laughter being the most frequent reaction.
The resulting map highlighted the neck, armpits, abdomen, and soles of the feet as primary hotspots. Interestingly, the study found that the groin and inner thighs only became primary hotspots when the tickling was initiated by a romantic partner, suggesting that social context alters physical sensitivity.
How great apes mirror the human tickle response
The findings published in Nature Human Behaviour suggest that tickling is an evolutionarily rooted trait shareed across hominids. Great apes, the closest living relatives to humans, engage in nearly identical behaviors, using their hands and fingers to target the same sensitive areas as humans do.
This primate parallel suggests that tickling serves as a fundamental tool for social interaction. in both humans and great apes, these behaviors are most common among individuals with close bonds,often involving an older individual tickling a younger one.
The 60% accuracy in spotting a 'tickle-giggle'
A separate 2024 study from the University of Amsterdam explored the speciific acoustics of ticklish laughter. researchers found that approximately 200 people could distinguish tickle-induced laughter from other types of giggles with about 60 per cent accuracy .
To verify these findings, the University of Amsterdam team used AI to analyze 887 YouTube clips . The analysis revealed that laughter caused by tickling exhibits significantly less vocal control and feels more invluntary than laughter triggered by a joke or a humorous mishap.
The shift from childhood play to adult restraint
The data indicates a clear demographic trend where the frequency of tickling decreases as individuals move from childhood into adulthood. This pattern suggests that tickling is primarily an "ancient play behavior" used during early development to foster social bonds .
This developmental decline echoes broader primate trends where play-fighting and tactile stimulation are central to juvenile bonding but fade as social hierarchies stabilize in adulthood.
The mystery of why humans and apes tickle
Despite the mapping of these hotspots, the precise biological function of tickling remains an open question. One theory proposed by the Radboud University team is that hotspots are located in areas not frequently touched in daily life, making the sensation a "surprise" response.
The source reports only the researchers' perspective on this evolutionary mystery, leaving it unclear whether tickling serves a protective purpose—such as guarding vulnerable areas—or if it is purely a social lubricant with no further survival utility.
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