science

Some glow in the dark chemicals are called phosphors, and while they're named after phosphorus, they usually do not contain any phosphorus, zinc sulfide for example. These are the kinds of things you might find on a watch face or stickers or whatever that need to absorb light from some other source first.

To make it even more confusing, phosphorus isn't actually phosphorescent, its glow is from chemiluminescence, the result of a chemical reaction.

And for what it's worth, stuff that glows under a black light is fluorescent.

I don't think phosphorus has ever been used for glowing tattoos, and if it was I'm pretty sure no one is still using it. We're well outside of my realm of expertise, but it should also be considered that how a chemical enters your body can make a difference in how toxic it is too, there's a whole lot of chemistry at work in your body, and ingesting something and absorbing it through digestion isn't necessarily going to have the same effect as absorbing it through your skin, there's a reason different medications have to be taken oral, allowed to dissolve under your tongue, given as a suppository, intravenously, intramuscularly, subdermally, etc. that said, I'm pretty sure phosphorus is bad no matter how you put it into someone's body.