Commonly-used mouthwash could increase risk of tooth damage, study finds

Researchers at the University of Plymouth found that commonly-used mouthwash could make saliva significantly more acidic

While many Britons use mouthwash each day to improve their dental hygiene, a new study has found that this could be more of a hindrance than a help. 

Researchers at the University of Plymouth have found that commonly-used mouthwash could make saliva significantly more acidic and increase the risk of tooth damage, in the first study of its kind.

The study, which examined the effect of chlorhexidine mouthwash on the oral microbiome, found it significantly increases the abundance of lactate-producing bacteria that lower the pH of the saliva. 

The work, published in Scientific Reports, involved 36 health participants being given placebo mouthwash for seven days, followed by seven days of a chlorhexidine mouthwash. 

At the end of each period, researchers then carried out analysis of the abundance and diversity of bacteria in the mouth, as well as measuring pH, saliva buffering capacity (which is the ability to neutralise acids in the mouth), lactate, glucose, nitrate and nitrite concentrations. 

It found that using chlorhexidine mouthwash over the seven days led to a greater abundance of species within the Firmicutes and Proteobacteria bacteria families, and fewer Bacteroidetes, TM7 and Fusobacteria. 

This change was associated with an increase in acidity, and chlorhexidine was found to reduce microbial diversity in the mouth. Researchers say more work is needed to determine if the reduction in diversity increases the risk of oral disease.

Dr Raul Bescos, who led the study, said: “There is a surprising lack of knowledge and literature behind the use of these products. 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.”

Dr Zoe Brookes, of the University of Plymouth’s Peninsula Dental School, said: “As dental clinicians, we need more information on how mouthwashes alter the balance of oral bacteria, so we can prescribe them correctly. This study is an important first step in achieving this.”