Take a look at your hand. If you zoomed in to the microbe level, you would make a startling discovery. Your hand is a zoo of bacteria!

But don’t run for the shower yet. Bacteria are just microbes. For the most part, they aren’t yucky at all. Less than one percent of bacteria make us sick. We call those pathogens. But why give those guys all the attention? Most bacteria are on our side. They fight pathogens and help us stay well.

You have probably heard that cells make up the human body. They do. But did you know that lots of your body isn’t . . . you? You have just as many bacteria in and on your body as you have cells. But bacteria don’t have your DNA. One scientist compared the bacteria in the human gut to a rainforest. Like the rainforest has many kinds of animals and plants, your gut has many kinds of bacteria. Some look like rods. Some look like spirals or spheres. The bacteria break down your food so you can digest it. Because of the work they do, your body can absorb nutrients. Once, scientists used guinea pigs to study this. Guinea pigs that lived in a place with little bacteria became malnourished and died. Their guts—just like yours—needed bacteria to do their jobs.

Are you a good zookeeper to the bacteria living in your body? It isn’t always an easy job. When bad bacteria get out of hand, you might take an antibiotic. But that doesn’t just kill the bad guys. It kills the good guys too. When that happens, you might want to fill up on good bacteria, or probiotics. That means eating some food with bacteria in it—on purpose! Don’t worry. You don’t have to get rotting food out of the garbage. Instead, you can eat yogurt, cheese, pickles, or sauerkraut!