Still, I get many e-mails asking me whether I offer 'black henna' tattoos, to which my answer is always No. This, as I am always explaining to people, is because there is no such thing as 'Black Henna'. Black henna is a name given to a body art substance which is not made from natural henna but instead includes chemicals such as PPD often used in hair dye. This PPD can cause a nasty allergic reaction and is considered by many as unsafe to use on skin. Although the body art looks good - I don't think it's ever worth the risk.
It's certainly frustrating to henna artists that this substance has been labelled as 'henna' as it often gives henna tattooing a bad name. So if you're interested in getting a temporary tattoo my advice would be to stick with natural brown henna. And if it looks jet black, it's certainly not henna.