WHAT CAUSES TICKLING SENSATION
Tickling is the act of touching a part of the body so as to cause involuntary twitching movements and/or laughter. The word “tickle” (help·info) evolved from the Middle English tikelen, perhaps frequentative of ticken, to touch lightly.The idiom tickled pink means to be pleased or delighted.
In 1897, psychologists G. Stanley Hall and Arthur Allin described a “tickle” as two different types of phenomena. One type is caused by very light movement across the skin. This type of tickle, called a knismesis, generally does not produce laughter and is sometimes accompanied by an itching sensation. Another type of tickle is the laughter-inducing “heavy” tickle, produced by repeatedly applying pressure to “ticklish” areas, and is known as gargalesis. Such sensations can be pleasurable or exciting, but are sometimes considered highly unpleasant, particularly in the case of relentless heavy tickling.