It's a circulation issue, as has been stated in IDCrewDawg's post already. I'm not a doctor, but I've read all over the place that the limit to wear pins should be around 30 minutes. While I'm guessing that is a safe limit for pretty much everyone and depending on how your body works, how tight the pins are, where they are set etc., you might be able to wear them longer....it's a message that stuck with me.

The incident I was talking about was a quite intense session with my former dom over the phone. He had me pretty worked up and busy, so I lost track. A nice thing really, but only if you can trust the domly one. Anyway, he'd asked me to put on the pins when we started talking and then things developed nicely from there. After the session, when he had me take off the pins, they looked and hurt pretty bad, but I thought (as you did) that it had only been around half an hour. I asked him about this and he told me that it had actually been almost two hours.

I didn't have any problems other than very sore nipples for the next day, but I still freaked. It might even have been alright, had he been there to monitor the state I was in - over the phone with a pretty tranced out sub - I thought it was over the top. Only one milestone that made me doubt he was right for me.

Again, I don't know how 'scientific' the 30 min limit is, or whether it's more of a thing similar to expiration dates for food (i. e. that it's safe to consume them without a doubt until that date)...but I've seen it over and over again. I'd be willing to risk longer exposure again since it went alright the last time, but ONLY if my dom was there to make sure I was alright. And besides, there's so much fun to be had if you take off and reapply them from time to time...big delicious OUCH!!

I'd talk to him about it, tell him that you were worried afterwards, maybe point him to this thread if he cares to do so. And if he acts like a big know-it-all I'd be worried. But I hope he'll be open enough to learn and have your safety and well-being as top priority.

Just my two cents.