So, many of the teachers at my school regularly gargle water and then spit it out. Not mouthwash, not water with salt in it, just straight water out of the tap. I have a good idea of the frequency because I can hear it happening from across the room. So I asked one of the repeat offenders why he does it, and he replied that it was for his health. He continued that it can help people avoid catching colds or the dreaded influenza by cleansing the mouth.
My first mental reaction was "that's the stupidest thing I've ever heard". The microbes that cause colds must be able to live in a watery environment because they are hanging out in your mouth in the first place, and there are probably about a million trillion of them chillin' out in there at any one time. Spitting out those germs would be like spitting out bad breath, or spitting out the little creatures that cause tooth decay. In other words, it ain't gonna happen.
But now that I was aware of the practice, I realized that it wasn't just a couple crazy old teachers, but that this was an official position from people that should know better.
This little sign is posted above one of the sinks in the teacher's room. It reads "Prevent infectious disease with hand washing and gargling!". It is issued by the Tochigi Prefectural Government.
The headline of this one is something like "Influenza is prevented by everyone!" The trifecta of good health is apparently gargling, hand washing, and wearing a mask when ill. This is also a message from our friends at Tochigi Prefecture. A worthwhile little addendum to this is that the kids have no access to hot water at school as far as I know. Not only does this seem to lessen the effectiveness of hand washing, but it probably discourages the practice altogether because the water is painfully cold in the winter.
I searched a bit to see if I could find any references to this and I found an article from the Health Behavior News Service (here). Headlines don't get much better than this: "Gargling May Prevent Colds, Study Says; Expert Finds Results Hard to Swallow". To summarize, Japanese researchers found that "the common cold could be prevented over 30 percent of the time by daily gargling with water." An American smart person, on the other hand, suggested the study was flawed because "while the researchers found a “borderline statistically significant effect” for water gargling, there was no true placebo group — that is, there was no control group in which people could gargle with “fake” water".
Not only does it seem to be impossible to due a proper experiment with gargling, I think that the practice has some religious significance that might be influencing people's views. Upon entering temples it its a common practice to ritually cleanse your mouth. Surely there's a connection.