During diving season(read year round) the third finger on both of my hands develops this same thing. I don;t know why none of the others do. I keep them trimmed short and use super glue and apply some of the wife's clear nail polish. In fact I'm gonna have to do another app today sometime. It;s a pain but it does work. She uses the Sally Hansen Hard As Nails stuff. Seems to be a better grade than the generic crap from wally world.
