A friend of mine was recently diagnosed with throat cancer, and he now faces a grueling regimen of radiation and chemotherapy, with the chances of success not at all certain. I couldn't figure out why he would get that cancer - he neither smokes nor drinks. Then I learned yesterday - 50 years of gargling Listerine twice a day. It is the high alcohol content that did it, according to his oncologist.
The idea that an alcohol based mouthwash can cause cancer is controversial. For example, Wikipedia assures us that there is no evidence that Listerine causes "mouth cancer", citing the American Dental Associations approval of the product. (When I went to the dentist for a cleaning the other day, his office gave me a "goody bag" that included a small bottle of the stuff.)
Googling the issue turns up this from the University of Maryland Medical School site:
Some studies have shown that mouthwash with alcohol content increases the risk for oral cancer. In addition, other studies have shown that smokers and people who drink alcohol tend to use mouthwash more often, linking all three factors together.
Another site states that
Listerine USED TO be made with over 26% industrial alcohol. Recent studies in USA by the National Cancer Institute of America have found that mouthwashes with an alcohol content of 25% or higher may be responsible for some mouth, tongue and throat cancers. Unfortunately the alcohol can act like a solvent making the gums and mouth tissues more vulnerable to carcinogens. Studies have shown that men had a 60% higher risk and women a 90% higher risk of these cancers compared to those not using mouthwash. Nowadays the alcohol content has been reduced to 21.6% but I would still be rather wary of excessive usage of this product.
There doesn't seem to be much doubt in the mind of my friend's physician. Why take the risk when there are plenty of mouthwashes out there that have no alcohol in them?