When a pathogen enters the body and reproduces, it can cause an infection, damage body cells, and cause illness symptoms that eventually lead to disease. Therefore, its prevention requires breaking the chain of infection.

The chain begins with pathogens: bacteria, viruses, fungi, prions, or parasites such as protozoa helminths. These can be present on the skin as transient or resident flora, or they can be acquired from the environment. Identifying and treating the type of infection and applying antimicrobial medications are essential. It is also essential to limit the growth of pathogens in the environment. Outbreaks of infection occur because the pathogen is transmitted to a reservoir, such as a human or animal, either directly or indirectly.

Then through the portal of entry, the pathogen enters a susceptible host; this access allows the pathogen to multiply in tissues. Direct transmission occurs through skin-to-skin contact, kissing, sexual intercourse, and soil or vegetation containing infectious organisms. Indirect transmission occurs through air particles, inanimate objects such as vehicles, or animate environments such as vectors. Indirect transmission is often controlled by hand hygiene, use of personal protective equipment, personal hygiene, first aid, safe removal of catheters and tubes, safe surgical procedures and prevention, and proper sharps disposal.

Finally, the host's susceptibility depends on genetic or constitutional factors, specific immunity, and nonspecific factors that impact an individual's ability to resist infection or restrict pathogenicity. Immunizations, treatment of underlying disease, health insurance, patient education, adequate nutrition, and screening of healthcare staff can reduce the susceptibility.