Tickling causes pain, so why do we laugh?

"Why do you laugh when you get tickled?" asked Samantha Waitley, 8, a third-grader at Townline Elementary School in Vernon Hills.

Tickling is often a way to show affection. Babies and little kids are quick to react when someone says they're going to tickle them, laughing almost before they're even touched.

"When you tickle someone, you actually stimulate the unmyelinated nerve fibers that cause pain," said Dr. Alan Hirsch, founder of the Smell & Taste Treatment and Research Foundation in Chicago. Hirsch has conducted hundreds of studies on the senses and is now working on a study called "The Pinocchio Sign" that could reveal ways to identify untruthful behavior.

Feeling ticklish has to do with the way your brain works. Touch triggers nerves that send impulses to the brain to figure out what the response should be. You can't tickle yourself - there's no element of surprise. And you aren't ticklish on body parts that are usually exposed like your hands and legs. You probably won't be ticklish, Hirsch said, if you don't know or trust the person who's tickling you.

Hirsch said that the sensation that makes you feel ticklish instead of feeling pain has to do with sensory perception.

Laughing is an emotional expression. Scientists aren't exactly sure what part of the brain creates the laughter response, but they do know that laughter reduces stress.

"Without question, some people are more ticklish than others," Hirsch said.