If you're feeling crummy, it's probably because nasty bacteria or some other germs have gotten into your body and made you sick. Bacteria are so tiny that you can't see them with just your eyes, but there are thousands, millions, even billions of them all over you, inside and out! This might sound kind of gross, but lots of bacteria actually help our bodies. The good bacteria are good for us, and the bad bacteria can make us sick. They may be to blame for your next sore throat or ear infection!