Yep, teenagers get into all manner of weird things, and this is yet another one.
When I was a teenager I had a thing for piercing my ears. I had 12 holes in my ears at one point, I let them close over, re-pierced them again a few years
later, some closed up again, I re-pierced them again... All up I think I've stuck a needle through my ears about 4 dozen times. I currently have 11 earrings and my tongue is pierced. I've pierced the ears of several friends as well - but I utterly refuse to even consider piercing any other part of a body, though I've been asked to many times. My brother has his ear pierced and at one point had his nose pierced. Some friends of mine have had so many piercings that they gained a few extra pounds from the weight of all the metal - well, alright, that's an exaggeration, but some people do go a little overboard with it.
There are a few things that need to be considered with piercings. Firstly, piercing ear lobes is easy and there isn't really any qualification necessary to do that. Hairdressers have been piercing ear lobes for decades, there is no age restriction on it in most places, and some parents now days even get their baby's ears pierced. Although I can do it easily, and I've never had any complaints, I am not going to explain how here. Reading about it is one thing, seeing it done is another, and I'm not going to encourage anyone to try it without being properly shown how to first. Ask your local hairdresser.
Other piercings are a totally different ball game. Specialized equipment is required, and specialized jewellery has to be worn. You can't use a piercing gun for a tongue piercing, and you certainly can't stick a normal earring in your tongue! Body piercings are not only different in where they are on the body, but because of where they are they can also vary in how they are pierced, the care required while they heal, how long they take to heal, and what type of jewellery can be worn. Body piercers should be properly qualified, should abide by health regulations and safety standards, and should also abide by any age restrictions. Different places have different restrictions on age for body piercings, though the restrictions are usually the same as for tattoos, particularly with regards to piercing genitalia.
Unlike tattoos, most piercings do go away and close over once the jewellery is permanently removed. The only exception to this is when the hole has been stretched too much. It seems to be a fashionable thing for some people to expand piercings to create wide holes that, when the jewellery is removed, leaves a large gap in the flesh. This is most commonly done for ear lobes, but I've also seen it done with nose piercings and I've heard of it with some genital piercings (particularly with the labia major in women). Otherwise, the hole closes over and leaves a tiny white scar which, in time, fades away. So there is no need to freak out about the long term effects for most piercings as, in most cases, there aren't any.
There are some things that need to be considered however. Firstly, piercings damage living tissue cells and can bleed. This may be a cause of concern for people that have a problem with severe haemhorrage (excessive bleeding). The piercing equipment should be sterilized before every use, as the risk of contracting blood-borne diseases is an issue if it isn't. Again, check that the person doing the piercing obeys the health and safety regulations. Piercings in some parts of the body can damage veins and nerves, so the body piercer may, after examining the area, refuse to do the piercing if they believe that there is such as risk. Again, they should be properly qualified. The biggest health risk is infection. The piercing must be properly cared for until it is completely healed. The body piercer will provide all the information required on how to look after it. If infection does set it, a consultation with a doctor is required. In many cases, a course of antibiotics will solve the problem, however, when severe enough, often the piercing will need to be removed. A lot of pain and discomfort for nothing is a good reason for not slacking off on the hygiene.
Body piercings, when done properly, don't really hurt very much at all. For most people it becomes more painful a couple of hours later when the swelling sets in and your body starts to fully realise that there is a foreign object stuck in it. Swelling can be a social problem as well as a health problem, as it does look a little odd to see someone with one eyebrow three times the size it is supposed to be. Most piercings take about 4 weeks to heal on average and are most uncomfortable for the first week. Forgetting they are there and bumping them or snagging the jewellery on something is the most painful problem that occurs. Most people that have body piercings will be able to relay all manner of funny little stories about their mishaps with forgetting they had the piercing done.
Piercings can cause more damage than bargained for. Tongue piercings can damage teeth. Eating food with a fork becomes an interesting new skill to learn as the prongs tend to catch the bar and as you pull the fork out of your mouth the bar wants to go with it - and that can hurt a lot, especially when the piercing is fresh. Not to mention the social embarassment of learning how to talk with it, and try re-learning how to whistle! Eyebrows, lips, and nose piercings can easily get snagged and pulled, and are especially bad if you are unfortunate enough to get into a physical fight - and what teenager at some point doesn't do that? Earrings are bad enough, but when the jewellery is screwed on through your lip or eyebrow, it can be torn out in a very nasty manner. Similar problems can occur with other piercings. This needs to be considered before an accident happens and large chunks of flesh are torn out and nasty scarring occurs.
People get piercings for all manner of different reasons. For some it is a cultural thing. For most people it's a fashion thing - that is, they believe it looks cool. For others, it's a pain thing. Some get piercings for sexual purposes. I found it quite annoying at the time when I got my tongue pierced, when people found out they would often comment about how my boyfriend must be happy about it. HA! I was single, I wasn't seeing anyone, and that is not the reason why I got it done. I got my tongue pierced to overcome my fears - the thought of someone sticking a bloody big needle through my tongue terrified me, so I did it. That may sound crazy, but I have never claimed to be anything but that, though most people that know me well enough have totally understood. So never presume to know why a person has or wants a body piercing, it could be any number of reasons, regardless of what type of piercing it is.
Having visible piercings can create a certain social stigma that isn't necessarily nice. Some close-minded sections of society look upon people with body piercings as if they were drug addicts, social outcasts, criminals, and freaks - and may treat them as such. Many employers have restrictions on piercings, some will even refuse to employ people with body piercings in the first place. For most people, having to remove the jewellery for an 8 hour shift will cause problems with the holes starting to close over in that time, and the jewellery then becomes painful to put back in - if indeed it can be put back in. As body piercings can be significantly uncomfortable until properly healed, and they can be expensive to have done in the first place, many people are loathe to comply to such rules in the workforce, and thus it makes it harder to find and keep a job. The same problems can occur at school. This becomes an issue of weighing up priorities - and teenage priorities are not the same as for adults - another thing that has to be learned by the teenager and their parents alike.
Although it may initially seem like a bad idea for your teenager to get a body piercing, there is not much reason to be too overly concerned. Talk to your child about it, find out what sort of piercing they want and why they want it. Find out about the risks and care requirements for that specific type of piercing by talking to a reputable body piercer, and discuss these with your child. Make sure they fully understand what they are getting themselves into, both physically and socially. Also make sure they are willing to accept the risks and the responsibility, they have considered all the potential negative aspects, and that their reasons for wanting the piercing are reasonable and well thought through. Keep in mind that - unless they go for over-stretching the hole which takes many months to do anyway - any piercing that is done properly is removable and should cause no permanent damage, so if they regret it later, they can undo it and write it off as a learning experience.