What is the germ theory of disease?

The germ theory of disease, also called the germ theory, or the microbial theory of disease, is the predominant scientific theory for understanding the cause of disease. It states that microorganisms such as bacteria, viruses, fungi, or other pathogen microorganisms cause most infectious diseases.

Proposed and supported by scientists such as Ignaz Semmelweis, Florence Nightingale, Joseph Lister, and most notably Louis Pasteur in the 19th century, this theory overturned two previously believed explanations for disease: the miasma theory and the theory of spontaneous generation.

The discovery that microorganisms can cause disease has led to the development of preventive measures (such as immunizations, antibiotics, pasteurization, and improved hygiene practices) that helped reduce the impact and incidence of infectious diseases.

The germ theory remains central to modern medicine and continues to be developed and refined as scientific understanding advances.