Just came across this rather scary titbit. I have never used a mouthwash (phew! relief!), but those who use an alcohol-based one on a regular basis would be well-advised to read this Telegraph UK article: http://tinyurl.com/8uwlsh

(Acetaldehyde, by the way, is the chemical that causes hangovers, see: http://en.wikipedia.org/wiki/Acetaldehyde)