Tickling, the act of lightly touching someone else's skin to make them laugh or squirm, is caused by stimulating nerve endings. Nerves run throughout the body, sending signals from the skin and internal organs to the brain, where they are translated into sensations. The sensation of tickling occurs when nerve endings are unexpectedly touched lightly. Expected touches or heavier touches do not generally result in a tickle, and we cannot tickle ourselves.
Ticklish Places and Nerve Endings
Nerve endings can be found at many locations on the body, including the armpits, back and chest. According to scientist Christine Harris, who studies ticklish behaviour and laughter, feet are one of the most ticklish places on the body for many people because of the many nerve endings there.
While for most people tickling causes laughter--a reaction that stems from the unexpectedness of the tickle and constant movement of touch--tickling can also be unpleasant. Overstimulating nerve endings through tickling can become painful if it is continued for long periods or if a person is more sensitive than most to the sensation.
Some scientists see tickling and tickle play as an early system for teaching the body self-defence. Tickle fights teach young humans and primates where they are sensitive, how much touch they can tolerate and how to protect sensitive areas.