Listerine mouthwash may increase the risk of some cancers, a new study has claimed.

A study from the Institute of Tropical Medicine in Antwerp, Belgium found that daily use of Cool Mint mouthwash is linked to increased “opportunistic bacteria” in the mouth.

These bacteria were previously linked to causing gum diseases, oesophageal and colorectal cancer, and systemic diseases, according to the study. 

There was also a decrease in a group of bacteria called Actinobacteria after using the mouthwash, previously found to help regulate blood pressure. 

Listerine study

The researchers came upon their findings during an investigation into the effects of daily mouth use on STI risk among gay men.

Some 59 men used Listerine Cool Mint for three months, followed by a “placebo mouthwash” for a further three months, or vice versa. 

Swabs of the men were taken and studied before the study, after using the Listerine and after using the placebo.

They found that Streptococcus was the most "abundant" bacteria found in swabs and higher in those who had used Listerine for three months compared to the control and placebo groups.

The researchers behind the study are warning that regular use of Listerine should be “carefully considered”.

'No evidence'

Listerine is owned by Kenvue, formerly the Consumer Healthcare division of Johnson & Johnson. 

It also owns brands such as Aveeno, Neutrogena and Tylenol. 

A Kenvue spokesperson said there is "no evidence Listerine causes cancer".

"We continuously evaluate the latest science and monitor safety signals to evaluate the benefit-risk profile of our products," they said.

They said Listerine is one of the "extensively tested mouthwash brands in the world" and the most recent study "exhibits several methodological issues".

"The findings in this paper do not provide evidence of any adverse health effect, lacking several important design controls and adequate rigor to make any conclusions about potential impact to human health," they said.