It has been suggested that long-term usage of mouth rinses with antiplaque and antigingivitis activity could possibly lead to an effect on the microflora, with an undesirable succession of opportunistic species occurring, or selection of species that develop resistance to the antimicrobial mouth rinse.1

A 6-month, randomised, double-blind study by Minah et al. demonstrated that the twice-daily use of LISTERINE® versus control rinse had no adverse effects on the normal balance of bacteria types in the mouth (n=83):1



Minah GE et al. 1989. Dental plaque samples analysed for microbial content by darkfield microscopy.

The study also showed that LISTERINE use did not promote the emergence of more dangerous opportunistic pathogens, including staphylococci or enteric bacteria.1

A second study compared LISTERINE® with a control rinse, with the aim of identifying microbial shifts. The composition of supragingival plaque was characterised prior to treatment and at 3 and 6 months following twice-daily supervised rinses with LISTERINE® or a hydroalcohol control. Microbial samples were harvested from the surfaces of 4 teeth in each subject and characterised by conventional methods.2

No significant differences were found with respect to the presence of presumptive oral pathogens either between or within treatment groups. In addition, no emergence of opportunistic pathogens was observed. However, there was a trend toward a decrease in the total microbial flora recovered in the LISTERINE® treatment group at both 3 and 6 months compared to pre-treatment levels. This appeared to be due to a decrease in the total anaerobic counts recovered and resulted in an overall decrease in the anaerobic/facultative count ratio. This is a favourable response since the organisms implicated in gingivitis usually require anaerobic culture.2

This study indicates that long-term use of LISTERINE® antiseptic resulted in a decrease in total supragingival plaque and did not produce a shift in the microbial composition of plaque that would be detrimental to oral health.2


  1. Minah GE et al. Effects of 6 months use of an antiseptic mouth rinse on supragingival dental plaque microflora. J Clin Periodontol 1989; 16: 347–352.
  2. Walker C et al. Evaluation of microbial shifts following long-term antiseptic mouthrinse use. J Dent Res 1989; Abstract 1845.