Germ theory of disease

Germ theory holds that many diseases are caused by microorganisms that enter a host and multiply there. It links specific infectious agents to disease and supports prevention through hygiene, sanitation, and targeted treatment.

Pathogen: A biological agent that causes disease in a host. Germ theory explains disease by identifying pathogens as its causal agents.
Miasma theory: The historical theory that disease was caused by harmful vapors or polluted air. It was a major rival explanation before germ theory gained acceptance.
Antisepsis: The prevention of infection by destroying or inhibiting microorganisms on living tissue. Antiseptic practice uses microbial causation to reduce infection during procedures.
Microorganism: A microscopic organism, including bacteria, archaea, fungi, and protists. Microorganisms include many of the agents implicated by germ theory.
Spontaneous generation: The discredited idea that living organisms can arise from nonliving matter under ordinary conditions. Experiments against spontaneous generation helped establish that microbes come from existing life.
Infection: The entry, establishment, and multiplication of a pathogen in a host. Infection describes the process by which disease-causing microbes inhabit a host.
Ignaz Semmelweis: A Hungarian physician who showed that handwashing sharply reduced childbed fever deaths. His hospital findings demonstrated infection control before microbes were widely accepted as the cause.
Aseptic technique: Practices that prevent contamination by disease-causing microorganisms. It prevents pathogens from reaching wounds, instruments, and sterile environments.
Bacteria: Single-celled microorganisms without a membrane-bound nucleus. Bacteria cause many diseases central to the theory's historical development.
Humoral theory: An ancient medical model that attributed health and illness to the balance of bodily fluids. It explains disease through internal imbalance rather than invading microorganisms.

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