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Why are people ticklish?

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📓 The short answer

When someone touches ticklish spots, your skin sends signals to your brain, triggering reflexes like squirming and laughter. Ticklishness likely evolved to protect sensitive areas of the body and to promote social bonding.

📚 The long answer

When you think about it, tickling is a particularly odd part of the human experience. As you're getting tickled, you're squirming away while telling your tickler to stop – yet you're giggling the whole time.

Tickling is perplexing to say the least. So let's tickle your fancy and dive right in. To start, there are two distinct types of tickling.

Knismesis refers to a light tickling sensation, such as when a stray hair brushes against your skin, and it does not typically induce giggling. Many other non-human species have this mechanism, and the evolutionary value is pretty straightforward: knismesis can alert you to insects crawling on your skin so you can brush them off.

Gargalesis is the type of tickling more commonly associated with humans. This is the hands-on tickling that makes you laugh and squirm, and the type of tickling we'll explore going forward. So what's happening physiologically when we're getting tickled?

What is happening when we are being tickled?

Your skin contains millions of nerve endings that sense physical stimuli, such as touch and pressure. When someone tickles you, mechanoreceptors – specialized nerve endings that detect touch and pressure – send signals to your brain. Tickling is especially sensitive on areas like your sides, underarms, and feet, where mechanoreceptors are highly concentrated.

From there, signals are sent to two important areas of your brain. The somatosensory cortex interprets the physical aspects of tickling, such as pressure and location, while the anterior cingulate cortex evaluates the emotional context, like deciding if the tickling feels playful because it's coming from a friend or invasive if it's coming from a stranger.

The brain's processing of the tickling sensation also triggers certain autonomic responses including squirming and giggling. Tickling triggers reflexive movements to withdraw from the tickler, likely as a protective mechanism for sensitive areas. Interestingly, the reflexes we have when we're getting tickled are similar to someone in severe pain.

Tickling also elicits reflexive laughter, an involuntary autonomic response. Research suggests that this laughter isn't necessarily a reflection of how much fun you're having; it's likely an emotional reflex to ease the tension you're feeling. These brain-activated reflexes show that tickling seems to straddle the line between pain and pleasure.

Why are some people not ticklish?

Some people seem to be immune from the effects of tickling. The reasons why aren't fully understood, but here are the factors that have an impact on how ticklish someone is:

• Skin sensitivity: If someone has more sensitive skin, they'll likely be more ticklish.
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• Age: Children seem to be more ticklish than adults. This may be because your nerve function changes as you age or it could be that children more often interpret tickling as playful, while adults can find it to be invasive and less enjoyable.
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• Mood: Emotions like anger seem to make you less ticklish, whereas feelings of anxiety can make your more ticklish.
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• Temperament: There have been studies showing that your overall propensity to laugh and smile is positively correlated with feelings of ticklishness. Simply put, if you're easy to laugh, you're easy to tickle.
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• Medical conditions: If you have neuropathy, issues with your nerve endings, you may have reduced sensation in certain parts of your body, and thus less tickling sensation. On the flip side, in rare cases neuropathy can actually make people more ticklish.
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• Genetics: Ticklishness likely has a genetic component as well. A 2015 study of twins found that identical twins were more likely to be similarly ticklish than non-identical twins.

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--- Thanks for reading this week's newsletter! If you have any thoughts, questions, or favorite GIFs, my inbox is always open. Just hit reply to send me a note! :) ​ All my best, Caitlin ​Click here to read five facts about Caitlin​

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​Sources for this week's newsletter​

📖 Book of the week

​Breath: The New Science of a Lost Art by James Nestor​

We all gotta breathe. Might as well learn how to do it right.

Nestor explores the impact that certain breathing techniques can have on our health and well-being, backed by scientific research and historical practices from around the world. I was impressed/disturbed when the author shared his experience doing an experiment on himself breathing only through his mouth for weeks on end. I've never been more grateful to be able to breathe through my nose.

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​Check out the full list of books I've recommended here.

👀 Catch up on other curious questions

• ​What causes brain freeze?​​
• ​Why is soccer not a popular spectator sport in the United States?​​
• ​Why does bright light cause some people to sneeze?​​

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