A microbe is a living thing so tiny you need a microscope to see it. The word comes from Greek roots meaning “small life,” and that's exactly what microbes are: incredibly small organisms that exist all around you and even inside you right now.

Microbes include bacteria and single-celled creatures like amoebas. Some microbes cause diseases like colds or strep throat, but many are harmless or even helpful. The bacteria in your stomach help digest food. Yeast microbes make bread rise and turn grape juice into fizzy drinks. Other microbes break down dead leaves in forests, returning nutrients to the soil.

Scientists estimate there are more microbes on Earth than stars in the universe. A single teaspoon of soil contains about a billion of them. Your skin is covered with millions of microbes that actually protect you from harmful ones trying to invade.

Before microscopes were invented in the 1600s, people had no idea microbes existed. When scientists finally saw these tiny creatures, it revolutionized medicine and helped explain how diseases spread. Understanding microbes led to huge advances: pasteurization to help keep milk safe, antibiotics to fight infections, and vaccines to prevent some diseases.