Why do we laugh when we are tickled?

Some people find getting tickled unbearable, some laugh until they cry and some don’t even crack a smile. They are unfazed. While there has been no solid evidence found on the reason people experience ticklishness, scientists have come up with differing theories over decades. There are two types of tickling: 

• Gargalesis: It is an aggressive form of tickling caused by someone touching the sensitive areas of the body repeatedly. 
• Kinesis: It can be caused by a light motion on the skin that can be self-induced. 

Scientists speculate that each type of tickle produces markedly different sensations because the signals are sent through separate nerve pathways.

Charles Darwin posed that the reason we laugh when tickled is the same as the cause of laughter triggered by a hilarious joke. It depends on the person’s state of mind.  An opposing theory by Sir Francis Bacon states that even in a grieved state of mind, people are unable to resist laughing when tickled. Here are some other theories behind the physiology of ticklishness.

Social Bonding 
Some scientists believe that the laughter response to ticklishness is developed in the first few months of life, which helps babies bond with parents. For children, much like roughhousing, tickling is also a form of playing around that strengthens their social bonds.  

Defense Mechanism 
According to one school of thought, we evolved ticklishness as a way to hone our response to the way our body’s sensitive and vulnerable areas are approached. It becomes a sort of natural combat training to protect these areas from harm. 

Reflexive Response 
Some studies that disprove the social bonding theory show that people who are ticklish will laugh in response regardless of whether they are being tickled by a human or a machine. It infers that ticklishness might just be a reflexive response. Being tickled stimulates our hypothalamus, the area of the brain in charge of our emotional reactions, our fight or flight and pain responses. The body movements of someone being tickled often mimic those of someone in severe pain. 

Animals feel ticklish too  
Humans are not the only organisms 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 that the rats are most ticklish along the belly and the bottoms of the feet. However, they did not show a similar response to being tickled when they were under distressing conditions. This indicates that there might be some credibility to Darwin’s ‘light state of mind’ theory.