How can bacteria be harmful to humans?

How does the body know which bacteria are good for it and which are not?

Dear Dr. Mo,

I read about bacteria. It said that innumerable bacteria live on and in our body! I'm worried now that this is dangerous! Bacteria make you sick, right?

Many greetings, Esther

Dear Esther,

what you have read is correct: our bodies are teeming with bacteria. Our body consists of 100 trillion cells - that is an incredibly high number. But ten times more bacteria live in and on it. But I can calm you down!

Most of the bacteria that colonize the human body are completely harmless. Many of these bacteria even work with him, such as B. those in the colon. Most of them live here too. The bacteria that live on the skin are also good for us. They produce substances that protect the body from the invasion of harmful bacteria.

By the way: Bacteria are tiny living things called Microorganisms. They only consist of a single cell. Some are round, others long, some agile, but above all: most species are still undiscovered.


However, some bacteria can actually harm people and make them sick if they enter the body. But we are well prepared: our immune system then knows what to do. And it works like this: All body cells have certain characteristics, such as surface characteristics. These are known to the immune system. Harmful bacteria that invade the body have different surface characteristics.

Now the antibodies are used. They are part of our immune system. Based on the surface features, they track down the intruders. Then they are destroyed by the phagocytes, which are also part of the immune system.

So do not worry! Most of the bacteria that are on and in your body are not dangerous - on the contrary.

Kind regards, Dr. Mon