The apostle Paul warns against "mutilators of the flesh" in Philippians 3:2. In many false religions self-mutilation is common. Also today we see various forms of self-cutting among people with psychiatric illnesses.
Questions may come up, whether piercing and tattooing is a form of self-mutilation. People who have a piercing or a tattoo usually argue that it is a form of self-expression and not a mutilation. This article describes the phenomenon of self-mutilation from a biblical perspective including the consequences of self-harm and this article focuses on piercing.  This article describes the differences between self-expression and self-mutilation from a (secular) psychological standpoint. The Mark of the Beast, as mentioned in Revelation 13, is a very serious evil mutilation. That's worth another study.

I think we shouldn't judge people on the fact that they have piercings or tattoos. We need to notice that born-again Christians may claim that their bodies are temples of the Holy Spirit, as 1 Corinthians 6:19 exclaims: "Do you not know that your bodies are temples of the Holy Spirit, who is in you, whom you have received from God? You are not your own." God is the master-healer. He can do immeasurable things with mistakes we may have done in the past.