At first, using a tampon might seem like a big deal to a girl. But once you get more comfortable with it, you might even forget you have one in.But that can be a problem if you forget for too long. Tampons should be changed every 4-6 hours. If not, bacteria can grow and cause an infection. You also might notice an odor. Leaving a tampon in too long also increases your risk of a serious illness called toxic shock syndrome.If you do forget about your tampon, remove it as soon as possible. One common mistake is to insert a new tampon without removing the old tampon. If that happens, remove both.Toxic shock syndrome is rare, but be sure to tell a parent if you are feeling sick and you recently left a tampon inserted too long.