Lisa wrote a great article on ear piercing on the site, but I wanted to weigh in on why we decided to let our daughter get her ears pierced at all and when she did (seven). I had read somewhere to wait until the kids were older, and one site suggested twelve years old. That's what we were going with, but then Helena asked me about it, so I re-researched the same issue.
I never found the original site that had suggested twelve as an age. However, I did find other sites that gave a lot of information about allergies, though only some of that information was useful. You can do the same research if you want, but it'll save you some time by reading what I found.
First off, I'm glad we did not pierce her ears as an infant. I found several forums with people who were upset about the lack of choice for those girls, which I can see a little, but I also found two forum posts from mothers whose daughters ended up with torn earlobes. While I'm not sure if it was a result of the body not being formed enough when the procedure was done or from little babies pulling at their own ears, the fact remains that at least some kids end up with problems from infant piercings.
I also found two studies online, one from Europe and one from South America, which stated that kids who got their ears pierced had much higher rates of nickel allergies than kids who did not get their ears pierced. The studies concluded it was based on age and the cheaper materials used in costume jewelry (nickel). Basically, you don't want any nickel touching an open wound, especially on a young child. One study suggested there was little difference for prevalence of allergies for any child before twenty years of age. Furthermore, it was suggested that the safest age to get one's ears pierced if after thirty. I found one site that suggested that girls who get their ears pierced after eleven may develop some kind of discoloration. I decided that since she's bound to get them herself in middle school (instead of waiting until she turns thirty) if we don't do it for her, it made sense to just get it done the best way possible, after infancy, before eleven.
From my research, I found that stainless steel or plastic would be the best. Lisa went with plastic. Apparently, cheap gold often has nickel, as does cheap steel. Lisa goes into a lot of this in her article.
Mostly, we caved a little to the peer pressure she will receive, and we have no problem with certain coming of age activities, as long as they don't scar our kids for life. Even if the cases I read about are isolated, at least I tried to get some information. Bottom line: don't just do this spur of the moment because she's nagging you or because your cousin's baby got pierced ears. Find out what works best for you and weigh the concerns you may have. This article can be one of your resources.