Henna tattoo artist “Jacob,” 20, affirmed that a lot really find henna tattoos dirty. But still others want them because it’s one way of expressing one’s emotions.

A real henna tattoo, on the other hand, fades to brown on the skin as it dries, and it will only last a few days -- so be wary of a shop that advertises tattoos that last longer than that.

That’s because an extra ingredient included in the longer-lasting “black henna” tattoos in wide use today — hair dye including p-phenylenediamine, or PPD — can cause nasty allergic ...