I wondered why Listerine kills microbes since it only has about 20-21% alcohol. It turns out that the essential oils in it also kill microorganisms as well.
formulations should not contain ingredients that diminish or compete with the activity of this cationic group.48
Essential oils mouthrinses act killing microorganisms by disrupting their cell walls and by inhibiting their enzyme activity.15,24 Antimicrobial mouth-rinses containing essential oils have a combination of thymol (0.064 percent), menthol (0.042 percent), eucalyptol (0.092 percent) and methyl salicylate (0.060 percent), as active ingredients. Listerine (Johnson & Johnson Consumer & Personal Products Worldwide, Morris Plains, New Jersey, USA) was tested for efficacy against oral bacteria as early as 1884, by the legendary W. D. Miller. In his paper “Microorganisms of the human mouth”, Miller stated that “Listerine has proved to be a very useful and active antiseptic”.28 In 1929, an independent assessment of this essential oils mouthrinse showed it to have significant bactericidal activity against a variety of microorganisms and concluded it to be safe and effective.
The combination of essential oils has shown to be safe and effective as an over-the-counter anti-plaque and antigingivitis agent. In an in vitro study, Ross et al.41 (1989) showed that essential oils killed a wide range of microorganisms within 30 seconds in the presence of serum. Jenkins et al.19 (1994) showed that in an in vivo single rinse model, the use of an essential oils mouthrinse can significantly reduce the levels of recoverable salivary bacteria compared to a negative control rinse for periods of up to 5 h. Although some experienced an initial burning sensation and biter taste, accommodation usually occurred in a few days and occasional tooth staining has been noted, but most clinical studies did not report this condition.48 Clinical studies have shown that essential oils retarded the formation of supragingival plaque and decreased the degree and severity of gingivitis. Additionally, the antimicrobial activity of the essential oil mouthrinses has been shown in saliva,13 in the gingival crevice, and on the dorsal surface of the tongue.34,35 Plaque reduction has ranged from 20% to 34%, and gingivitis reduction, from 28% to 34% when essential oils were used twice daily following tooth brushing.17,18
About 80 to 90% of the oral malodor originates locally in the mouth, and the bacterial overgrowth is the major etiological factor. In many cases, bacterial overgrowth is associated to poor oral hygiene, gingivitis and periodontitis, coating on the tongue, cavities and throat infections.29 Additionally, oral malodor affects from 40 to 50% of the population in different levels.30 In vitro, oral bacteria, as well as oral specimens such as saliva, plaque and tongue coatings, can produce the volatile sulfur compounds including hydrogen sulfide, methyl mercaptan, dimethyl sulfide, as well as compounds such as indoles and skatoles22 that contribute to the complex mixture of odorous molecules found in the exhaled air. In vivo, factors that support the growth of these bacteria will predispose a person to malodor. Examples include accumulation of food within pockets around the teeth, among the bumps at the back of the tongue, or in small pockets in the tonsils.23,37 Some studies have recognized that a diminished saliva flow also represents an important factor to malodor. A reduced saliva flow increases the concentration of bacteria in the mouth and worsens bad breath.45
The tongue represents a special place for the colonization of microorganisms, including dental and periodontal pathogens. Indeed, the tongue is colonized immediately after birth and anaerobic species can be detected prior to the eruption of teeth. Their numbers and the presence of other anaerobes increase at the time of the primary eruption of teeth.
To eliminate oral malodor, home oral hygiene procedures are recommended to reduce accumulations of debris and the presence of bacteria. These procedures include tooth brushing and flossing, brushing the tongue or using a tongue scraper. Mouthrinses act against the malodor caused by oral bacteria when used as a complement to mechanical means, since by controlling bacteria it is possible to control malodor. The effects of mouthrinses could be due to thymol and eucalyptol, the volatile oils that have proven activity against bacteria. Kato et al.20 (1990) showed that bacterial counts plummet in as little as 30 seconds following a mouthrinse with thymol and eucalyptol. However, if the etiology of the oral malodor is related to periodontal disease, regular dental care is recommended to prevent or treat these pathologies.7,9