That’s a bit glib, and ignores the possibility that now it’s known those nanoparticles travel in lymph, they could be found elsewhere. In the case of something like TiO2, I’d be pretty concerned if nanoparticles where found in my lymph nodes or elsewhere. There is also evidence of chronic enlargement of the nodes as a result, and persistent hypertrophy or inflammation are known risk factors for cancer. Simply dismissing any risk until large longitudinal studies show a correlation in key populations is probably unwise.

It’s been known for a while that tattoos are a possible vector for some infectious diseases, typically when unsanitary methods are employed. The focus of disease and tattoos has generally been around Hep C, and you might be overestimating the degree of scholarly interest in looking beyond that. Nanoparticles infiltration is a relatively new concept, and none that I’ve ever seen leads me to the conclusion that the results are likely to be positive, but it’s early days yet. TiO2 has been tentatively linked to tumors in rats, but it’s only been tested through the inhalation route. Science takes time, and a rational person might wait and see rather than say “fuck it, until you prove it I’m tatting up!”

So sure, get a tattoo, but realize that you’re having an unregulated ink shot into your dermis, and elements of that ink can infiltrate systemically. That would worry me, but then, I wouldn’t get a tattoo.