Did you know that most of the cells in your body aren’t yours?

The human body is made up of tiny building blocks called cells. Each part of your body is made up of cells that do a certain job: hair is made of hair cells, blood is made of blood cells, muscles are made of muscle cells. They’re also really tiny: you could fit about 40 of your body cells in a straight line across the head of a pin. That means we need a lot of cells in our bodies. About a hundred trillion!

If we look inside a cell, one of the things we find is DNA. This is like a blueprint for your body that tells each cell what its job is. Even though we have different kinds of cells, each one has the same copy of this blueprint.

But our bodies don’t just belong to us. They’re also home to tiny living things called microbes that are only one cell big, and their cells are much smaller than ours are. They have their own DNA, which is completely different from the DNA you find inside each of your cells. They live all over our bodies, but like certain places best: our underarms, our intestines, and our mouths are absolutely full of them.

In fact, a human body is like a walking, talking hotel for microbes. There are twenty times as many microbe cells in your body than there are cells that contain your DNA. That means most of the cells in your body aren’t even yours!