The practice of wearing face masks to protect against disease is actually nothing new. Mask wearing for the specific purpose of warding off disease was common (and even sometimes mandated by public health regulations) as far back as the 1918 "Spanish" flu pandemic, and the beaked "Doctor Schnabel" plague mask dates back to at least 1721.

I'm curious when face masks were first identified as protective against disease. Were the 18th century "beak" masks a revolutionary new idea, or was masking to prevent disease already a thing?

To be clear, I'm not asking about the development of the modern germ theory of disease or when the first formal medical study demonstrating the effectiveness of masks to a modern-day level of rigor was published. I am asking about the development of a substantial belief or theory that mask-wearing prevents disease, even if the reason was not known or the modern empirical evidence of that belief or theory would not come for many years.

The wearing of masks for cultural, religious, fashion, or climate reasons does not count.

The discovery of the effectiveness of face masks counts even if the contemporary medical theory behind the mask was completely wrong by 21st century standards. For example, if there is an ancient Egyptian medical textbook that states, "Respiratory disease is caused by the ghosts of executed criminals, so when disease is around, we wear masks to scare off the ghosts.", it would count since it would demonstrate an understanding that a link exists between masks and disease.

The practice of wearing face masks to protect against disease is actually nothing new. Mask wearing for the specific purpose of warding off disease was common (and even sometimes mandated by public health regulations) as far back as the 1918 "Spanish" flu pandemic, and the beaked "Doctor Schnabel" plague mask dates back to at least 1721.

I'm curious when face masks were first identified as protective against disease. Were the 18th century "beak" masks a revolutionary new idea, or was masking to prevent disease already a thing?

To be clear, I'm not asking about the development of the modern germ theory of disease or when the first formal medical study demonstrating the effectiveness of masks to a modern-day level of rigor was published. I am asking about the development of a substantial belief or theory that mask-wearing prevents disease, even if the reason was not known or the modern empirical evidence of that belief or theory would not come for many years.

The wearing of masks for cultural, religious, fashion, or climate reasons does not count.

The discovery of the effectiveness of face masks counts even if the contemporary medical theory behind the mask was completely wrong by 21st century standards. For example, if there is an ancient Egyptian medical textbook that states, "Respiratory disease is caused by the ghosts of executed criminals, so when disease is around, we wear masks to scare off the ghosts.", it would count since it would demonstrate an understanding that a link exists between masks and disease. For the avoidance of doubt, any appearance of mask recommendations for the prevention of disease appearing in medical literature or public health orders counts even if the evidence of efficacy of such masks provided in such sources does not meet modern standards.

The practice of wearing face masks to protect against disease is actually nothing new. Mask wearing for the specific purpose of warding off disease was common (and even sometimes mandated by public health regulations) as far back as the 1918 "Spanish" flu pandemic, and the beaked "Doctor Schnabel" plague mask dates back to at least 1721.

I'm curious when face masks were first identified as protective against disease. Were the 18th century "beak" masks a revolutionary new idea, or was masking to prevent disease already a thing?

To be clear, I'm not asking about the development of the modern germ theory of disease or when the first formal medical study demonstrating the effectiveness of masks to a modern-day level of rigor was published. I am asking about the development of a substantial belief or theory that mask-wearing prevents disease, even if the reason was not known or the modern empirical evidence of that belief or theory would not come for many years.

The wearing of masks for cultural, religious, fashion, or climate reasons does not count.

The practice of wearing face masks to protect against disease is actually nothing new. Mask wearing for the specific purpose of warding off disease was common (and even sometimes mandated by public health regulations) as far back as the 1918 "Spanish" flu pandemic, and the beaked "Doctor Schnabel" plague mask dates back to at least 1721.

I'm curious when face masks were first identified as protective against disease. Were the 18th century "beak" masks a revolutionary new idea, or was masking to prevent disease already a thing?

To be clear, I'm not asking about the development of the modern germ theory of disease or when the first formal medical study demonstrating the effectiveness of masks to a modern-day level of rigor was published. I am asking about the development of a substantial belief or theory that mask-wearing prevents disease, even if the reason was not known or the modern empirical evidence of that belief or theory would not come for many years.

The wearing of masks for cultural, religious, fashion, or climate reasons does not count.

The discovery of the effectiveness of face masks counts even if the contemporary medical theory behind the mask was completely wrong by 21st century standards. For example, if there is an ancient Egyptian medical textbook that states, "Respiratory disease is caused by the ghosts of executed criminals, so when disease is around, we wear masks to scare off the ghosts.", it would count since it would demonstrate an understanding that a link exists between masks and disease.