I now believe that compulsive piercing and tattooing is a sign of epithelial insensitivity caused by long-term high blood sugar or hyperinsulimia. If you can stand the pain, chances are you can't feel it.
The reason we do it is- Puncturing the skin and tissue activates your sugar suppressed immune system. That's why you feel good for a few weeks afterwards. But then want to do it again after it heals...
Back in the day- it was mostly alcoholic men who had tattoos.
Now it's very many young women.
It's become a very popular and socially acceptable form of self-injury due to our population-wide excessive sugar consumption.