The vagina has an amazing ability to expand. After all, a baby can come through there. But in reality, it's only a few inches deep. When you put in a tampon, it stays in your vagina. The only other opening is at the top of your vagina but it's really tiny. So there's no way the tampon can get out and go anywhere else inside your body. Before you start using tampons, you may want to talk about them with your doctor. Obviously, you shouldn't use them if you haven't started your period yet. Once you use tampons, they should be changed at least every 3 to 4 hours.