Not the fairytale you expected
This link has some rather graphic images. It tells the story of a man in Eastern Europe who has a rare condition that causes him to have "keratin-like matter growing out of the skin on hands and feet". It is officially called Epidermodysplasia verruciformis, and may be caused by a papillomavirus (warts).
Simply put, it's not just gross, but probably very sucky for the poor man. It certainly puts paid the "growing extra nails and turning into mermaid" from Paul Jennings' short story Nails. As you can see from this picture, it doesn't cover his entire body yet, it is sort of progressing like a slow human petrification progress. Neither article mentions if its painful. I wouldn't think it would hurt any more than normal warts, it would probably be quite uncomfortable. The physical distortion also looks like his hands are practically useless. No piano for you.