The immune system is your body's defense system. It helps protect you from illness and infection. The immune system usually reacts to and attacks bacteria, viruses, and cancer cells. An allergy is when your body's immune system reacts to something harmless, such as food, plants, or medicine.
The immune system is your body's defense system. It helps protect you from illness and infection. The immune system's job is to attack things that don’t belong in your body, such as germs, parasites, and cancer cells.