Don't overdo a good thing- they can be quite erotic over the nipples, but if you leave them on for too long you can create the most disgusting looking blister in the world. It's not painful, but the only cure is time. I've had them on for minutes many, many, times without problem. Another time they were on for more than an hour- thought nothing of it. The first one came off- fine. The second once came off and there was a blister from the edge of the nipple to the edge of the areola.