The sensation of being ticklish occurs as a physiological response to unexpected touch when the somatosensory cortex and anterior cingulate cortex in the brain produce two messages via the central nervous system that combine to produce a pleasant sensation, reports Josh Clark for HowStuffWorks. The same nerves that interpret the tickling sensation also report sensations of hot, cold and pain to the brain's neurological pathways.
Clark elaborates that tickling has the potential to go too far; if enough pressure is applied to a person for an extended period of time, the sensation of being tickled can quickly become uncomfortable or even painful.
The brain also uses the ticklish response as a warning or protection mechanism through the use of small hairs on the body, similar to the way cats, dogs and other mammals rely on the use of their whiskers to alert them to unexpected stimulation. This can help alert people to the presence of bugs such as mosquitoes, spiders, ticks, ants and flies that may be crawling over areas of the skin unnoticed.
People commonly laugh as a reaction to being tickled not because they find the act of feeling ticklish funny, but because they are exhibiting a subconscious reaction of submitting to their aggressor's action.