NBR can certainly fail RoHS depending on the plasticizers that they use. Certain chemicals cause cancer etc. From a medical perspective, much safer to use silicone, which are also available in some hardware stores as viton, but are usually reddish in color. Although silicone can come in any color that you like.

*correction, viton is not silicone, but still used in medical applications

I know nothing about piercings, but I can tell you that you 100% don't want to use hardware store o-rings in your ears. Nothing good can come from that.

Do not put things in your body not made to put in your body.

Components from hardware stores have all kinds of composition. If you don't know what it's made from, why would you assume it's safe?

Even "stainless steel" can have all kinds of different compositions, some highly allergenic, some out-right toxic.

Unless you're sensitive to nitrile you should be able to, but the best ones are silicone (the clear ones). Source: worked in a body art studio for about a decade

It sounds like a lot of people here are incorrectly assuming you are going to wear the o ring as jewelry, instead of using it as a keeper for your jewelry.

The o rings are the same. Wash them and use them.

Afaik, the standard orings are exactly the same material as in standard orings. Obviously, you can get stuff made of other materials, but your average black rubber oring is~~n~~ the same material, no matter where you buy it. And I know for a fact that in the early days of body modification, when people were making their own plugs, they used orings from a hardware store. There weren't any specialty ones at all.

Now, over the years, there arose more decorative options, which often required a change in materials. Can't make glowy orings out of the same rubber, you dig? But the typical ones you find on mass produced plugs are ordered from the same places that the hardware store ones get made.

I'm not saying that all plug makers order from the same places, just that when you're churning out thousands of plugs, you either make your own orings, or you're ordering them from somewhere. When that somewhere is also mass producing their orings, you are going to end up ordering what they make unless you're ordering enough to merit them setting up another production line for your needs.

Again, afaik, there isn't a piercing specific oring maker that's selling to plug makers. It's all coming from the same suppliers in China for the most part.

The caveat: been over a decade since I was hanging out with people that were serious about body mods enough to be making their own stuff and ordering supplies in bulk. Shit could have changed since then. I doubt it, but if anyone that's currently making plugs on a large scale says otherwise, they'd know better than I do.

I would suggest washing them first, but you definitely can. I have 00 plugs and have lost the o-rings on them more than once ... and the hardware store has been great for replacements. Just make sure that you get the right size.

You might also want to consult a doctor as they'd most likely be an unbiased medical expert for knowing about using products meant to be worn on or used in the body

Meh, clean it first and it'll probably be alright. If if have issues stop using it.