Not all bacteria are harmful. Most bacteria are your friends, not your enemies. Good bacteria can help you digest food and make essential vitamins, while harmful bacteria can make you sick. Some bacteria in our body will protect you from harmful bacteria.

1. Bacteria in the respiratory tract can block dust in the air and prevent harmful bacteria from entering. They can also secrete a viscous liquid, which wraps harmful bacteria and turns them into phlegm and excretes them.

2. Lacrimal gland cells can secrete a bactericidal chemical, which moistens and sterilizes eyes day and night.

Gland cells in the stomach secrete an acid, which can be used to destroy all suspected harmful substances.

However, due to various reasons, some harmful bacteria will still break through the layers of blockade and enter the depths of the human body. This requires mobilizing human cell guards to fight.