Countries vary in how stringently they regulate chemicals in tattoo inksIvanRiver/ShutterstockWhether it is a butterfly on your ankle or your football teams logo across your back, tattoos have long been seen as a way of expressing individuality, as well as sometimes having cultural significance. Yet research is just starting to scratch the surface of their potential health effects.Tattoo pigments are made up of numerous chemicals. In the European Union, the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) legislation has set concentration limits for around 4000 compounds in such pigments, mostly due to cancer concerns.