My pathophysiology teacher gave us an interesting current article to read on tattooing.

A couple of NAU undergrad students are researching "tattoo inks to determine if any inks pose health threats in the form of heavy metals or other dangerous chemicals." I quote one of the students. "I don't think anyone is aware that the FDA doesn't regulate the tattoo process. The inks in tatoos are subject to regulation by the U.S. Food & Drug Administration as cosmetics, but the FDA does NOT regulate tattoo ink for injection, nort does it regulate tattooing itself." The article continues by saying, "...the various inks do not have to have ingredients listed. So far they have found that some inks have as many as 14 elements in them, with some instances of lead. But just how much of these elements exist in the inks has yet to be measured. Gathering quantitative data is the next step." Here's a link to the article if you want to read it in its entirety.
http://www4.nau.edu/insidenau/bumps/3_17_05/tatoo.htm

Since this research has surfaced, other "reports have surfaced indicating that tattoo ink can cause adverse effects in wearers, such as allergic reactions, burning sensations during MRI scans, and the migrationof tattoo ink into different areas of the body, including the lungs." That quote was from:
http://health.excite.com/article/id/524476.html