Prior to the 19th Century, what was the common term for the belief that foul air caused infections?

The belief that foul air or "bad air" was responsible for causing diseases is commonly referred to as the miasma theory. This concept suggests that diseases, particularly those affecting the lungs or causing fevers, were caused by unpleasant odors emanating from decomposing organic matter or other environmental sources. Miasma was thought to be a poisonous vapor that could lead to infections and illnesses by merely inhaling the contaminated air.

The miasma theory dominated medical thinking for many centuries, influencing public health approaches and urban planning, as efforts were made to improve air quality and manage waste to prevent the spread of disease. This understanding persisted until the advent of germ theory in the late 19th century, which shifted the focus from environmental factors to microorganisms as the actual causative agents of disease.

In contrast, contagion refers to the idea that diseases can be transmitted from one individual to another, germ theory posits that specific germs cause specific diseases, and the pathogen hypothesis is a more modern concept aligned with germ theory, focusing on understanding how different pathogens interact with hosts.