Source: scienceblogs.com
Author: Francis Mawanda

If you are like me, you probably always and almost faithfully, include a bottle of mouthwash on your grocery list especially after watching and/or listening to the numerous commercials in the media which claim that you will not only get long lasting fresh breath, but also freedom from the germs that cause plaque and gingivitis. However, many proprietary mouthwashes including my favorite brand contain Alcohol (ethanol) which also gives them the characteristic burn we have to endure, albeit for a few seconds each day, but safe in the knowledge that the product is hard at work killing all the germs that give us bad breath and may cause plaque and gingivitis. But the question I continually ask myself is whether regular or long term use of these products is safe especially after reading the numerous research reports and newspaper articles suggesting a possible link between long term use of alcohol based mouthwashes and oral cancer.

Several research studies have reported finding an association between long term mouthwash use and oral cancer (1, 2, 3). For example, in a study conducted by Wynder and colleagues (1), they found a significant association between mouthwash use and oral cancer. A bigger multi-site study by Guha and colleagues (3) comparing participants who reported having used mouthwash to those who reported never having used mouthwash found that individuals who reported using mouthwash more than twice a day were nearly six times more likely to develop oral squamous cell carcinoma compared to those who reported never having used mouthwash. However, in both these studies, no distinction was made on whether participants used alcohol or non-alcohol based mouthwashes which raises several epidemiological concerns such as specificity, since not all mouthwashes contain the same chemical ingredients

However, several studies have been conducted in which a distinction was made between alcohol containing and non alcohol containing mouthwash use (4, 5, 6). Unfortunately, these studies have produced mixed results. While some studies reported finding a positive association between alcohol containing mouthwash use and oral cancer (4), other studies found no association at all (5, 6). For example, although a 1983 study conducted in the states of California, Atlanta, and New Jersey by Winn and colleagues (4) found an increased risk of oral cancer among users of alcohol containing mouthwash compared to both non-users and users of non-alcohol based mouthwash, a similar study conducted in Puerto Rico found no significant association between the use of alcohol based mouthwash and oral cancer.

To add to the confusion is the fact that reviews of the subject by epidemiologists and other experts have also produced mixed results. While some researchers in their reviews concluded that the results of these studies provide sufficient evidence to demonstrate a link between long term use of alcohol based mouthwash and oral cancer (7, 8), other researchers concluded that the evidence is not sufficient to make the conclusion that there is an association between alcohol based mouthwash use and oral cancer (9,10).

Furthermore, while systematic reviews or meta-analyses can give us a better picture of the association between use of alcohol based mouthwashes and oral cancer because they can generate a pooled risk estimate by aggregating all the findings on the subject, there has only been one meta-analysis on this subject which was conducted by epidemiologists in Europe (10) and concluded that there is no excess risk for oral cancer from use of alcohol or non-alcohol based mouthwash.

From all this confusion, it’s clear that a randomized control trial (RCT) is needed to determine with a higher degree of certainty whether there is a true association between long term use of alcohol based mouthwashes and oral cancer. However a RCT is not feasible in this case simply because it would be unethical to expose individuals to a product that may cause cancer however weak the association maybe. Possible alternatives include quasi-experimental studies, prospective cohort studies or repeated case-control studies which may provide sufficient evidence through consistency. However, results from these alternatives will still face criticism since they do not offer unbiased estimates.

Therefore, until concrete evidence is available, the decisions on whether to use mouthwash or not and whether to use alcohol based or non-alcohol based mouthwashes remains a matter of personal preference and of course cost for some of us.

References:
1. Weaver A, Fleming SM, Smith DB. Mouthwash and oral cancer: carcinogen or coincidence? Journal of Oral Surgery 1979;37:250-3.
2. Wynder E L, Kabat G, Rosenberg S, Levenstein M.Oral cancer and mouthwash use. J National Cancer Institute 1983; 70: 255-260.
3. Guha N, Boffetta P, Wunsch Filho V et al. Oral health and risk of squamous cell carcinoma of the head and neck and oesophagus: results of two multicentric case-control studies. American Journal of Epidemiology 2007; 166: 1159-1173.
4. Winn D M, Blot W J, McLaughlin J K et al. Mouthwash use and oral conditions in the risk of oral and pharyngeal cancer. Cancer Research 1991; 51: 3044-3047.
5. Winn D M, Diehl S R, Brown L M et al. Mouthwash in the etiology of oral cancer in Puerto Rico. Cancer Causes Control 2001; 12: 419-429.
6. Marshberg A, Barsa P, Grossman M L. A study of the relationship between mouthwash use and oral and pharyngeal cancer. Journal of the American Dental Association 1985; 110: 731-734.
7. McCullough M J, Farah C S. The role of alcohol in oral carcinogenesis with particular reference to alcohol-containing mouthwashes. Aust Dent J 2008; 53: 302-305
8. Werner C .W. & Seymour, R. A., Are alcohol containing mouthwashes safe? British Dental Journal 2009; 207: E19
9. La Vecchia C. Mouthwash and oral cancer risk: an update. Oral Oncology 2009; 45: 198-200.
10. Lewis M A O, Murray S. Safety of alcohol-containing mouthwashes. A review of the evidence. Dent Health (London) 2006; 45: 2-4.