I have the exact same problem as the previous poster that sam2004 posted. I'm 36 years old and have recently (within the last year) have had a problem with excessive moisture around the anus. Like sam, it only occurs when I feel the urge to have a bowel movement. The moisture does not stain, and does not smell like 'feces' though it does smell very 'musky'. I also suspect it is sweat. Recently the problem has become so bad that wetspots soak through my underwear and my pants, leaving embarassing dark spots right on my backside by the time I even feel the urge to go the restroom. So I end up going to the restroom several times in the morning the instant I feel any urge that suggests I 'could' go to try to head off the embarassing moisture before my co-workers see it. And to give my pants the chance to dry out.
I recently (within the last year) had a colonoscopy (my mother died from colon cancer so I'm starting those early) and I explained the problem to the doctor and his response was "you'll just have to live with it". A very insenstive answer in my opinion and considering that it's gotten worse to the point that I'm getting embarassed by it at work, something needs to be done. Considering Sam2004's problem, it may be somewhat related to IBS, and like sam, when I was in my 20's, had extreme abdominal pain when a bowel movement was imminent, though that happens very very infrequently to me now (once every 2 months maybe).
This problem is very frustrating and depressing frankly. It did help a great deal to see someone else has had the same problem though, for a long time I couldn't find anything on this anywhere.
This discussion is related to
Excessive Moisture Around the Anus.