I found this interesting article at Wired News just before bed tonight. I hope this doesn't give me bad dreams :)
Tattoo artist Richie, who lives and works in Colorado, has been offering UV blacklight reactive ink to his clients for most of his 4-year career. "Three and a half years ago, I was asked by a friend about the UV ink," Richie says. "So I did a little research and got a sample of the ink and all the paperwork explaining how it was made and how safe it is. After trying a small sample on myself, I began to use the ink." These are some of the results.