There are many different types of germs. Germs are found in all kinds of places. There are four major types of germs: bacteria, viruses, fungi, and protozoa. They can invade plants, animals, and people, and sometimes they make us sick.

Bacteria are microscopic, one-cell creatures that get nutrients from their environments in order to live. Sometimes the environment is a human body. Bacteria either reproduce outside of the body or inside of the body while causing infections. Some of the infections that bacteria cause are strep throat (streptococci), ear infections, cavities, and pneumonia. Even though most bacteria are harmful, some bacteria are good. The good bacteria live in our intestine and help our digestive system sort out the nutrients in our food, and the rest of the food is used as waste. Some bacteria are also used by scientists in labs to produce vaccines.

Viruses need to be inside living cells to grow and reproduce. Most viruses can't survive very long if they're not inside a living thing like a plant, animal, or person. A host is what the virus lives in. The host gives the virus what it needs to grow and reproduce. When viruses get inside people's bodies, they can spread and make people sick. Some viruses cause chicken pox, measles, flu, and many other diseases. Because some viruses can live for a while on something like a door knob or countertop, be sure to wash your hands regularly!

Fungi are multi-celled, plant-like organisms. Unlike other plants, fungi cannot make their own food using photosynthesis. Instead, fungi get their nutrition from plants, people, and animals. They love to live in damp, warm places, and most fungi are not dangerous. An example of something caused by fungi is athlete’s foot, which is an itchy rash that teens and adults sometimes get between their toes.

Protozoa are one-celled organisms that love moisture and often spread diseases through water. Some protozoa cause intestinal infections that lead to diarrhea, nausea, and belly pain.