Does Listerine Cause Cancer?

My hygienist scared me last week when she mentioned during my appointment that I shouldn't use Listerine or other alcohol-based mouthwashes. Like heavy alcohol consumption, it's been linked to increased level of mouth cancer, she said, and you should either stop using it or switch to a safer, non-alcohol type. I was skeptical that such an old, mainstream product could be carcinogenic, but she assured me that the medical studies were there to prove it. So I checked.

Short answer: she's wrong.

It's true that Listerine contains alcohol -- 21.6% by volume, something to keep in mind if Prohibition ever makes a comeback. Alcoholics are known to suffer from more cancers (especially mouth cancers) and there are studies which show a link. But alcohol does not cause cancer in the lab, so many scientists are skeptical of these studies, especially since high alcohol use can be associated with plenty of other bad habits, like smoking or high-stress lifestyles.

As for Listerine, the most exhaustive analysis to date, published in August 2003 in the Journal of the American Dental Association, concluded: "It is unlikely that the use of mouthwashes that contain alcohol increases the risk of developing [cancer]". They looked at nine studies, six of which flat-out concluded there was no link between mouthwash and cancer. Of the remaining three, one proved incorrect on a follow-up and the others suffered from clear sample bias. For example, many users of mouthwash are smokers -- if the study doesn't control for smoking, what good is it?

In fact, the Nov 1, 2006 issue of the Journal of the American Dental Association even went so far as to recommend it, along with brushing and flossing, as part of oral hygiene.