The fast-growing mouthwash category has been dealt a blow after new research showed ethanol-based products increase the risk of oral cancer by up to nine times.

A Melbourne University study of more than 3,000 people found a nine-fold increase in the risk of cancer among smokers and a five-fold risk among drinkers.

It is thought the ethanol helps cancer-causing carcinogens permeate the mouth lining, producing a substance called acetaldehyde.

Dr Michael McCullough, who was behind the study, urged retailers to remove alcohol-based mouthwashes. “We see people with oral cancer who have no other risk factors than the use of alcohol containing mouthwash.”

And the findings were supported by cancer and other groups. A Cancer Research UK spokesman said "alcohol definitely causes mouth cancer".

But Johnson & Johnson, manufacturers of leading brand Listerine, played down the scare. A spokesman said the product was safe and "the most extensively tested mouthwash in the world".

With extensive advertising by leading manufacturers, the mouthwash category saw 16% growth in sales in The Grocer's Top Products Survey (Nielsen, mat 4/10/08).