A number of case-control studies have suggested a link between mouthwash use and head and neck cancer.

The aim of this analysis was to provide more definitive evidence on the presence or absence of an association between mouthwash use and head and neck cancer using individual-level data on a very large number of cases and controls

Methods

All studies in the International Head and Neck Cancer Epidemiology Consortium (INHANCE) with data on mouthwashes were used. Pooled data from 12 case-controlled studies including 8,981 cases (83.0% confirmed squamous cell carcinomas) and 10,090 controls was combined. In most studies, controls were frequency-matched to cases on the basis of age and sex. Cases were categorized by tumor site (oral cavity, N = 2790; oropharynx, N = 2632; hypopharynx, N = 577; larynx, N = 1793).

Logistic regression was used to assess the association of mouthwash use with cancers of the oral cavity, oropharynx, hypopharynx, and larynx, adjusting for study, age, sex, pack-years of tobacco smoking, number of alcoholic drinks/day, and education.

Results

• 74.3% of cases and 69.6% of controls were men; the mean age was 58.4 years (SD 10.7) among the cases and 57.9 years (SD 11.5) among the controls.
• The prevalence of ever mouthwash use among the controls was 42.7% (study- specific range 13.2–63.4%

	Head and neck cancer	Oral cancer
	Odds ratio (95% CI)	Odds ratio (95% CI)
Ever-use of mouthwash	1.01 (0.94–1.08)	1.11 (1.00–1.23)
Regular use of mouthwash	1.02 (0.94–1.11)
Long-term use of mouthwash (>36 years)	1.15 (1.01 – 1.30)	1.28 (1.06-1.56)
Long-term with higher frequency (>1 x daily) of use	1.31 (1.09 – 1.58)
Regular (>2 x daily), long-term (>35 years)	1.75 (1.25 – 2.48)

 Conclusions

The authors concluded

the results of this pooled analysis confirm recent systematic reviews and meta-analyses and multicenter studies that reported no overall increased risk of head and neck cancer in individuals who ever used mouthwash, but an association in long-term frequent users.

Comments

The authors’ highlight that all the included studies were case-control studies so may suffer from recall bias. They also note that there was no association with mouthwash use in never drinkers or never drinkers. Many mouthwashes contain alcohol in the discussion it noted that if the presence of alcohol on mouthwash contributed to the risk than an interaction with tobacco use as seen with alcohol might have been identified but this was not seen. The retrospective nature of the studies and the challenges in teasing out the various behaviours is something that well conducted prospective cohort studies (which have not been carried out to date) could help elucidate.

Links

Primary paper

Boffetta P, Hayes RB, Sartori S, Lee YA, Muscat J, Olshan A, Winn DM, Castellsagué X, Zhang ZF, Morgenstern H, Chen C, Schwartz SM, Vaughan TL, Wunsch-Filho V, Purdue M, Koifman S, Curado MP, Vilensky M, Gillison M, Fernandez L, Menezes A, Daudt AW, Schantz S, Yu G, D’Souza G, Haddad RI, La Vecchia C, Hashibe M. Mouthwash use and cancer of the head and neck: a pooled analysis from the International Head and Neck Cancer Epidemiology Consortium. Eur J Cancer Prev. 2015 Aug 13. [Epub ahead of print] PubMed PMID: 26275006; PubMed Central PMCID: PMC4752930.