Germ theory is, of course, the 19th-century proven idea that microscopic germs—pathogenic viruses, bacteria, parasites, and fungi—cause disease. It supplanted the leading explanation of disease at the time, the miasma theory, which suggests that diseases are caused by miasma, that is, noxious mists and vapors, or simply bad air arising from decaying matter, such as corpses, sewage, or rotting vegetables. While the miasma theory was abandoned, it is credited with spurring improvements in sanitation and hygiene—which, of course, improve health because they halt the spread of germs, the cause of diseases.

Germ theory also knocks back a lesser-known idea called the terrain theory, which we've covered before. This is a somewhat ill-defined theory that generally suggests diseases stem from imbalances in the internal "terrain" of the body, such as malnutrition or the presence of toxic substances. The theory is linked to ideas by French scientist Antoine Béchamp and French physiologist Claude Bernard.

Béchamp, considered a bitter crank and rival to famed French microbiologist Louis Pasteur, is perhaps best known for wrongly suggesting the basic unit of organisms is not the cell, but nonexistent microanatomical elements he called "microzyma." While the idea was largely ignored by the scientific community, Béchamp suggested that disruptions to microzyma are a predisposition to disease, as is the state of the body's "terrain." French physiologist Claude Bernard, meanwhile, came up with an idea of balance or stability of the body's internal environment (milieu intérieur), which was a precursor to the concept of homeostasis. Ideas from the two figures came together to create an ideology that has been enthusiastically adopted by modern-day germ theory denialists, including Kennedy.

It's important to note here that our understanding of Kennedy's disbelief in germ theory isn't based on speculation or deduction; it's based on Kennedy's own words. He wrote an entire section on it in his 2021 book vilifying Fauci, titled The Real Anthony Fauci. The section is titled "Miasma vs. Germ Theory," in the chapter "The White Man's Burden."