Yes, like a tampon, you're supposed to keep them in no longer than 8 hours at a time. I was seriously considering getting one of these cups, but when I found the time limit, that made it not worth my money or my while. I normally would change more often than eight hours, but I wanted something I could leave in up to, say, 14 hours, because I sleep more than 8 hours, and when I'm on my period, it can be up to 14, and I hate the mess when I wake up.