In this topic you will learn how your body fights disease.

Germs can go from one person to another. If you touch something with germs on it and then touch your nose, mouth, or food, the germs may get inside. There are many ways germs can infect your body. There are different kinds of germs. One type of germ is called bacteria. Bacteria are one-celled living things that can be helpful or harmful. Some harmful bacteria cause disease. Different kinds of harmful bacteria cause different diseases.

Another kind of germ is a virus. A virus is a tiny particle that can reproduce only in a living cell. When a virus enters one of your cells it makes that cell make hundreds of copies of itself. When the copies burst out of the cell, the cell dies. The copies of the virus are now free to enter other cells. Soon there are thousands of copies of the virus in your body.

Once germs get into your body, your body's white blood cells fight back. White blood cells are cells in the blood that fight bacteria and viruses. You have millions of these germ fighters inside you. The body also makes antibodies. An antibody is a chemical made by the immune system to fight a particular disease. Your immune system is all the body parts and activities that fight diseases.

Some diseases, like chickenpox, you get only once. Once your body has won the battle against a certain type of invading germ, your white blood cells will "remember" the germs they destroyed. If the same germ ever invades again, they will recognize it. Your white blood cells will attack and destroy the germ before it can make you sick. When your body kills a germ before it can make you sick, you have immunity. Immunity is the body's ability to protect itself or fight diseases caused by germs.

It is important to keep your immune system working at its best. It will be at its best if you eat healthfully, get plenty of rest, and make sure that you get all your vaccines. A vaccine is a medicine that causes the body to form antibodies against a certain disease.