"Inks, which are injected into the skin with small needles, have caused allergic rashes, chronic skin reactions, infection and inflammation from sun exposure, said Elizabeth Tanzi, co-director of the Washington Institute of Dermatologic Laser Surgery in Washington, D.C. A study published in July suggested that phthalates and other chemicals may be responsible for some of those problems.
That raises questions about more serious, long-term risks such as skin cancer, scientists say.
One of the chemicals found in black tattoo inks, benzo(a)pyrene, is a potent carcinogen that causes skin cancer in animal tests. Dermatologists have published reports in medical journals on rare, perhaps coincidental cases where malignant melanomas are found in tattoos.
Recently, the Food and Drug Administration launched new studies to investigate the long-term safety of the inks, including what happens when they break down in the body or interact with light. Research already has shown that tattoo inks migrate into people's lymph nodes."
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2011/09/05/BAJB1KSGO6.DTL&type=science