Tonight I was doing some mindless Internet surfing and came across an article (with accompanying slide show) called "What Your Nails Say About Your Health". In the middle of the slides I found out that rippled nails "may be an early sign of psoriasis or inflammatory arthritis."
My thumb nails are particularly rippled, with ridges running from the bottom to the tip. As far as I know I have no psoriasis or arthritis, so I decided to get a second Google opinion. This article told me that the most common reason for ridged nails is aging.
I liked that diagnosis much better, and think I'll go with it.
Five years ago today: Mama Needs A New Pair Of Shoes