Dipping into a subject that I kinda know a fair amount about...
Generally speaking, tattooing carries more risk actually than piercing because of the nature of the training/apprenticeship in the tattoo world versus piercing circles.
Tattoo artists have a WIDE variety of procedures for preparing for tattooing, doing the actual work, and the aftercare involved. Even how they bandage (if they bandage at all!) fresh tattooes will vary from shop to shop.
In piercing, most people who really know what they're doing (and the ONLY people you should be going to see for a piercing) have gotten their training from Fakir Musafar, the "father of the modern primitive."
Fakir's been doing body modification and shamanistic ritual since the late 1940's and has established the preimminent "school of thought" for body piercing and practice. he still runs educational programs and seminars and most "good" piercers have either learned under him or under someone who learned under him. There are certification documents to look for that say one has been trained in Fakir's methods...
Piercings should be treated like any type of (usually shallow) stab/puncture wound. They need to be kept clean and bandaged until they heal.
The same applies for tattoos and even branding (or scarification as it's called) but it's harder to keep those kinds of wounds clean without clearing out pigment that is supposed to stay put.
Generally most pigments used in tattooes are non-toxic, though some may cause allergic reactions and will usually be rejected by the body (scabbing up something fierce until it falls off wiht new skin, and no tattoo, underneath.
I have one tat, on my right calf above my ankle. I had been pondering piercings for quite a while but finally talked myself out of it.
Now, being on coumadin, I'd NEVER think of such a thing.
Same with tattoos.
And when I give the "lecture" to young adults (teens, etc.) that are thinking about getting a tat, I tell them I sat and thought about it for maybe three years before I actually got it. Tattoos are generally forever, you can sit and ponder it for months and years before getting one, it won't change the experience.
For the record, I have two buddies (twin brothers) who are vegan and nearly covered in tattoo work. Some of it's VERY impressive, but a lot of the early stuff they got were cheezy little things that have since been covered up by better work. They've also had their ear lobes piereced and stretched a bit, nothing more though. They seek out good artists and ask all kinds of questions, not only about the tattoo artist, but also asking about reputation through previous clients.
Fakir Musafar