The Psychology Of Tickling
Compared to pain, itching and other sensations, not much scientific research has been conducted into tickling. However even as far back as the 19th century, Charles Darwin was asking questions about tickling. Today, there is one researcher in particular, Christine R. Harris of the University of California, who has done several studies on various aspects of tickling.
Does being ticklish depend on an interaction with another person?
Arguably, no. In a study titled "Can a machine tickle?" Christine R. Harris and another researcher blindfolded students and told them they would be tickled on their foot once by a machine, and once by a researcher. They were asked to rate how much each tickled. Overall, the average scores were very similar - some even said the machine tickled more! In both cases it was actually a hidden assistant doing the tickling (Harris & Christenfeld, 1999).
Why can't you tickle yourself?
Some people can, but most of us cannot - and it may be because tickling served an evolutionary purpose. One theory is that being ticklish alerted our ancestors to spiders etc crawling over their bodies. When we try to tickle ourselves, our brain is aware that we are being touched, but also that we are doing it ourselves, and so our brain allows us to ignore our own touch but still know when we're about to be bitten!
The majority of research supports this general idea (Fridlund & Loftis 1990).
Why are some people more ticklish on one side of their body?
Nobody knows, but you're not imagining it. We know it doesn't depend on gender, or which side they use more. One theory is that the left side of the brain is involved more in positive emotions. If you consider being tickled a positive experience, it might explain why one study found that in general, people are more ticklish on their right foot (the study only measured ticklishness on feet). There hasn't been a study done to test this hypothesis (Smith & Cahusac, 2001).
Are women more ticklish than men?
Not measurably! None of the studies where data was available measured a significant difference in ticklishness between the genders (Harris & Christenfeld, 1997, Smith & Cahusac, 2001).
References:
Fridlund, A.J. and Loftis, J.M., 1990. Relations between tickling and humorous laughter: Preliminary support for the Darwin-Hecker hypothesis. Biological Psychology, 30(2), pp.141-150.
Harris, C.R. and Christenfeld, N., 1997. Humour, tickle, and the Darwin-Hecker hypothesis. Cognition & Emotion, 11(1), pp.103-110.
Harris, C.R. and Christenfeld, N., 1999. Can a machine tickle?. Psychonomic Bulletin & Review, 6(3), pp.504-510.
Smith, J.L. and Cahusac, P.M., 2001. Right-sided asymmetry in sensitivity to tickle. Laterality: Asymmetries of Body, Brain and Cognition, 6(3), pp.233-238.