The miasma theory, which proposed that diseases were caused by ‘bad air’ or noxious vapors, began to decline in credibility in the 19th century, particularly with the advancements in germ theory. The key turning point came in the 1860s, especially with the work of scientists like Louis Pasteur and Robert Koch, who demonstrated that microorganisms were the real culprits behind many diseases.
By the late 1800s, the germ theory became widely accepted, leading to the gradual abandonment of the miasma theory. This transition was solidified with the widespread implementation of sanitation measures and the understanding of infectious diseases. While the exact date of the miasma theory’s ‘disproof’ is difficult to pinpoint, its influence diminished considerably by the 1880s, with germ theory gaining overwhelming support from the scientific community.