The first study looking at the effect of chlorhexidine mouthwash on the entire oral microbiome has found its use significantly increases the abundance of lactate-producing bacteria that lower saliva pH, and may increase the risk of tooth damage.
A team led by Dr Raul Bescos from the University of Plymouth’s Faculty of Health in England gave a placebo mouthwash to subjects for seven days, followed by seven days of a chlorhexidine mouthwash.
At the end of each period, the researchers carried out an analysis of the abundance and diversity of the bacteria in the mouth—the oral microbiome—as well as measuring pH, saliva buffering capacity (the ability to neutralise acids in the mouth), lactate, glucose, nitrate and nitrite concentrations.
The research, published in Scientific Reports, found using chlorhexidine mouthwash over the seven days led to a greater abundance of species within the families of Firmicutes and Proteobacteria, and fewer Bacteroidetes, TM7 and Fusobacteria. This change was associated with an increase in acidity, seen in lower salivary pH and buffering capacity.
Overall, chlorhexidine was found to reduce microbial diversity in the mouth, although the authors cautioned more research was needed to determine if this reduction in diversity itself increased the risk of oral disease.
The research also confirmed findings from previous studies indicating that chlorhexidine disrupted the ability of oral bacteria to turn nitrate into nitrite, a key molecule for reducing blood pressure. Lower saliva and blood plasma nitrite concentrations were found after using chlorhexidine mouthwash, followed by a trend of increased systolic blood pressure.
“There is a surprising lack of knowledge and literature behind the use of these products,” Dr Bescos said.
“Chlorhexidine mouthwash is widely used but research has been limited to its effect on a small number of bacteria linked to particular oral diseases, and most has been carried out in vitro.
“We believe this is the first study to look at the impact of 7-day use on the whole oral microbiome in human subjects.”