Germs are found all over the world, in all kinds of places. The four major types of germs are bacteria, viruses, fungi, and protozoa. They can invade plants, animals, and people, and sometimes they can make us sick.
Bacteria (say: BAK-teer-ee-uh) are tiny, one-celled creatures that get nutrients from their environments in order to live. In some cases that environment is a human body. Bacteria can reproduce outside of the body or within the body as they cause infections. Some infections that bacteria can cause include ear infections, sore throats (tonsillitis or strep throat), cavities, and pneumonia (say: new-MO-nyuh).
But not all bacteria are bad. Some bacteria are good for our bodies — they help keep things in balance. Good bacteria live in our intestines and help us use the nutrients in the food we eat and make waste from what's left over. We couldn't make the most of a healthy meal without these important helper germs! Some bacteria are also used by scientists in labs to produce medicines and vaccines (say: VAK-seens).
Viruses (say: VY-rus-iz) 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. Whatever a virus lives in is called its host. When viruses get inside people's bodies, they can spread and make people sick. Viruses cause chickenpox, measles, flu, and many other diseases. Because some viruses can live for a short time on something like a doorknob or countertop, be sure to wash your hands regularly!
Fungi (say: FUN-guy) are multi-celled (made of many cells), plant-like organisms. Unlike other plants, fungi cannot make their own food from soil, water, and air. Instead, fungi get their nutrition from plants, people, and animals. They love to live in damp, warm places, and many fungi are not dangerous in healthy people. An example of something caused by fungi is athlete's foot, that itchy rash that teens and adults sometimes get between their toes.
Protozoa (say: pro-toh-ZOH-uh) are one-cell organisms that love moisture and often spread diseases through water. Some protozoa cause intestinal infections that lead to diarrhea, nausea, and belly pain.