Here is an article I can agree with : 

http://www.livestrong.com/article/180816-non-toxic-tattoo-ink-ingredients/


       I use Eternal ink. I have never had a problem with it before, and I know others that use it, that swear by it. But when it comes to any ink- there is no guarantee. Most people by now know that if someone has a problem with a certain color it is most always red. There is something in the red that can cause problems with the healing- I am not exactly sure why, but I came up with this idea-  the molecular structure of the pigment red is the biggest and most potent. Plus there is other reasons. You can do a red test by putting the ink on top of your skin and letting it dry, after wipe it off and see if there is an irritation, but still I am not sure how accurate this test is.
 It is a bummer too, I use red so much of my pieces...