Old Testament prohibitions regarding tattoos are considered ceremonial laws and thus are not binding on Christians. There is nothing inherently immoral about a Catholic having a tattoo or a piercing. What would make those things immoral would be its content/message/purpose. What message am I trying to send through this action? What is my motivation? It is essentially viewed as a morally neutral act whose morality depends upon content, context, and circumstances. Prudential judgment is needed.