Henna Tattoos Risks

Is BLACK henna dangerous?? answer me only the "pro" ones please!?

I wanna know if the Black Henna is that dangerous how the people and many sites do say...I wanna try to do some of black henna tattoos and i don't know the risk very much...

I've had about 3 friends have it happened.

It sinks into your skin, and goes into your bloodstream.
Can cause bladder cancer, asthma, and many other heath problems.

Diluting it with brown henna will do no good.
It will still be just as toxic as prior to diluting it.