Germ theory

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Overview

Germ theory holds that many diseases are caused by specific microorganisms that enter and multiply in the body. It replaced older explanations such as bad air, imbalance and moral failing. Once causes were known, they could be prevented through clean water, sanitation, antiseptic surgery, vaccines and later antibiotics. Alongside better nutrition and public health measures, this helped raise average life expectancy sharply in the twentieth century, and it changed how people thought about illness, blame and responsibility.

Context

Until the mid-nineteenth century, the leading explanation of epidemics in Europe was miasma, the idea that disease spread from foul air from decaying matter. Surgery was often fatal because of infection, and hospitals were dangerous. Microscopes had shown tiny organisms since the seventeenth century, but no one had shown that they caused disease. Cities were growing fast, with poor sanitation.