What theory explains that microorganisms are the cause of many diseases?

The Germ Theory of Disease is a foundational concept in microbiology and medicine that posits that many diseases are caused by microorganisms, such as bacteria, viruses, fungi, and parasites. This theory transformed our understanding of health and disease by introducing the idea that specific infections are the result of pathogenic organisms invading the body. It laid the groundwork for advancements in sanitation, hygiene practices, and the development of vaccinations.

This theory emerged in the 19th century through the work of scientists like Louis Pasteur and Robert Koch, who conducted experiments that demonstrated how particular microorganisms could cause specific diseases. The implications of this theory are profound, leading to improved public health measures and practices aimed at controlling infections and preventing outbreaks.

In contrast, the other concepts do not specifically identify microorganisms as the direct cause of disease. The Hygiene Hypothesis suggests that a lack of early childhood exposure to infectious agents might lead to an increased susceptibility to allergic diseases. Immunization Theory revolves around the practice of inoculating individuals with a vaccine to prevent disease, while Pathogen Theory, though closely related, is less commonly used in modern terminology compared to Germ Theory.