The grunge "revolution" brought about an increased interest in non-mainstream music, underground scenes, and a resurgence of punk rock. Some of the hallmarks of these scenes and styles were tattoos and aggressive body piercings. Initially, they were ways for people to set themselves apart from the mainstream. Like grunge itself, it didn't take long for the mainstream to co-opt these underground fashions.
It isn't necessarily correct to call them fads, because they never quite faded away the way pet rocks did in the '70s. Tattoos and piercings were so thoroughly absorbed into mainstream culture that today they're far more acceptable than they were 15 years ago. There are limits, of course. More extreme forms of facial piercing and obvious (or offensive) tattoos can definitely reduce employment opportunities. But there are plenty of school teachers and doctors with tattoos and piercings, and most of them are children of the '90s.