Cell, Tissues, Organs, Organ Systems, Organism (Multicellular).
This is from the smallest component to largest components that make up a human organism.
A cause for infection is pathogens entering the body. This is either to a disease that's being transferred from one being to another, or through toxins, wounds, and similar things. Most commonly, when fighting the infection, the body produces white blood cells to combat the infection, which in combination with medication usually defeats the infection.
