The ethanol in mouthwash is thought to allow cancer-causing substances to permeate the lining of the mouth more easily and cause harm.
Mouthwashes can cause oral cancer and should be removed from supermarket shelves, an expert said recently.
There is 'sufficient evidence' that those containing alcohol contribute to increased risk of the disease, according to a review of the latest studies by an Australian scientist.
Professor Michael McCullough, whose findings are published in the Dental Journal of Australia, said some mouthwashes were more dangerous than wine or beer because they contained higher concentrations of alcohol - as high as 26 per cent.
He said they should only be available with a prescription and for short-term use.
'We see people with oral cancer who have no other risk factors than the use of alcohol-containing mouthwash, so what we've done in this study is review all the evidence that's out there,' he said.
Smoking and alcohol consumption are well-established risk factors in oral cancer which is diagnosed in 5,000 people in the UK each year, and causes 1,600 deaths.
Professor McCullough, from Melbourne University, said the alcohol in mouthwash allows cancer-causing substances such as nicotine to penetrate the lining of the mouth more easily.
And it can mean a toxic breakdown product of alcohol called acetaldehyde - another carcinogen - can accumulate in the oral cavity when swished around the mouth.
The review reported evidence from an international study of 3,210 people which found daily mouthwash use was a 'significant risk factor' for head and neck cancer.