Germ theory denialism is the pseudoscientific belief that germs do not cause infectious disease, and that the germ theory of disease is wrong.[1] It usually involves arguing that Louis Pasteur's model of infectious disease was wrong, and that Antoine Béchamp's was right. In fact, its origins are rooted in Béchamp's empirically disproven (in the context of disease) theory of pleomorphism.[2] Another obsolete variation is known as terrain theory and postulates that germs morphologically change in response to environmental factors, subsequently causing disease, rather than germs being the sole cause of it.[3]