Why are we ticklish?

[LillyoftheValley]

I'm very ticklish. Depending on who's The Tickler, I sometimes refill my energy from laughter of tickling , and other times I think I'll die if I feel another tickle. And because it varies from pleasure to torture, I can't decide is it psychological or physiological phenomena?

[gberardi]

My girlfriend tickles me all the time. A friend once said to me "Soft tummy!", and I asked what she meant.

Apparently, if you just decide not to tense up, the tickling is no longer ticklish. I was amazed that it worked!

Of course, now whenever I try to do so, I laugh because "soft tummy" is just funny to say aloud in a tickle war, which results in tensing up, which results in being ticklish.

Which leads me to believe that the reason why you can't tickle yourself is because you need to have some tension, and I think it is too hard to tickle yourself and tense up at the same time.