Health & disease

Almost everyone has been ill at some point, with a cough, a runny nose, or a fever. Often the cause is tiny living things that are so small you can only see them under a microscope. They are called germs. In this chapter you will learn which germs exist, how they travel from one person to the next, and how you can protect yourself.

Bacteria and viruses

There are two especially important groups of germs. Bacteria are tiny living things made of a single cell. Many are even helpful and support digestion in the gut, only a few kinds cause illness. Viruses are ten to a hundred times smaller than bacteria and are not truly alive. They need a host cell to multiply. Colds and the flu are caused by viruses.

How infection happens

Germs do not get from one person to the next by themselves. They need a route that carries them across. When you sneeze or cough, tiny droplets full of germs fly through the air. On your hands they reach door handles or toys, and when you then touch your face, they travel onward. This is how one sick person can infect many others.

Protection through hygiene

Luckily you can do a lot to protect yourself and others. Washing your hands thoroughly with soap removes most germs. Sneezing into your elbow keeps droplets back. The body also defends itself: its immune system fights germs. A vaccination trains this immune system in advance, so it can stop a real illness more quickly.