The toxic truth about mouthwash

More than a third of us use mouthwash, whether that’s just for an extra burst of minty freshness after brushing our teeth or to tackle bleeding gums. However, rather than bettering the work of your toothbrush, this habit may actually be putting your health at risk.

For more than a decade, studies have suggested that mouthwash may raise the risk of some cancers. Now, fresh research has repeated this warning for users of one of the country’s favourite options. But you may not need to clear out your bathroom cupboards quite yet.

Dangers of mouthwash?

In the latest study from researchers in Belgium, which was originally investigating the impact of daily mouthwash on STI risk among 59 men, volunteers used Listerine Cool Mint daily for three months, followed by three months using a placebo mouthwash, or vice versa.

Interestingly, results also showed that the Listerine mouthwash, which rids the mouths of some germs behind bad breath and plaque, raised levels of two bacteria in the mouth (fusobacterium nucleatum and streptococcus anginosus) too. Separate research has linked these species to esophageal and colorectal cancer.

The theory is that the alcohol, antiseptics or flavourings found in mouthwash alter the microbiome and trigger changes in the growth pattern of the cells, which could influence the likelihood of cancer developing, explains Prof Karol Sikora, a renowned oncologist and honorary professor of professional practice at the University of Buckingham.

Additionally, a chemical called acetaldehyde is produced in the mouth after using an alcohol-containing mouthwash, notes Dr Zoe Brookes, an associate professor of dental education and research at the University of Plymouth. It’s this chemical that’s thought to be potentially cancer-causing, she adds.

In response to their findings, the study authors urged people against using mouthwash.

It’s not the first time this worrying link has been reported. A 2009 paper from the then-chair of the Australian Dental Association warned that mouthwashes that contain alcohol raise the risk of oral cancer. It referenced a 2007 study which found that the fluorescent liquid was linked with a three-fold higher risk of developing head and neck cancer.

However, none of this research proves that mouthwash causes cancer. And a 2023 review warned that evidence linking mouthwash and cancer is “limited and conflicting”, as other studies have found no link between mouthwash use and cancer.

Other studies have only flagged a cancer concern when that bacteria is found in the gut, she notes. “But just because fusobacterium may cause colon cancer in the gut, it doesn’t mean that bacteria in the mouth is going to cause oral cancer – it’s too far of a jump,” she says.

However, there are other risks. On top of the cancer concerns, some studies have linked frequent mouthwash use with diabetes and high blood pressure, says Dr Mia Burleigh, a senior lecturer at the University of the West of Scotland who researches the microbiome and oral health.

This is thought to be caused by mouthwash reducing the rate at which the mouth converts a compound found in food called nitrate into nitric oxide because it clears the mouth of certain bacteria.

“Healthy sources of nitrate include vegetables and roots such as dark leafy greens and beetroot,” she explains. “Without key bacteria in our oral microbiome, nitric oxide production is reduced, impairing glucose metabolism, insulin sensitivity and cardiovascular control through the regulation of blood vessel dilation.”

What’s in mouthwash?

While ingredient lists vary dramatically between mouthwashes, there are five key components found in most options on pharmacy and supermarket shelves, says Dr Tom Crawford-Clarke, a dentist and founder of Luceo Dental in London.

Fluoride is one of the most common. It protects the teeth against acids produced by plaque, which helps prevent tooth decay.

Antibacterial agents are also included reduce the number of microorganisms in our mouths and balance pH levels, which helps prevent tooth decay and tackles bad breath, he explains.

Examples include cetylpyridinium chloride, which prevents bad breath and plaque from maturing, as well as chlorhexidine digluconate, found in Corsodyl, which brings down bacteria levels, helping to control the early signs of gum disease.

Essential oils are also added to freshen breath, provide a “minty feeling” and reduce the build-up of plaque, while sweeteners are mixed in for taste, Dr Crawford-Clarke notes.

Alcohol is the ingredient that provides the “zing” effect of mouthwash that stings a bit, helps to dissolve oils in the liquid and kills bacteria. It is frequently found in concentrations of more than 20 per cent, which is around double that found in wine and four times more than beer. This is one of the reasons why you should never drink it.

The exact blend of ingredients you get will depend on which mouthwash you pick up.

The safest ways to cleanse your mouth and teeth

“If you’re worried about the research, just buy an alcohol-free mouthwash,” says Prof Brookes. “Then you can avoid what some researchers are claiming – that the alcohol content is raising the risk of cancer.”

Dr Burleigh recommends forgoing mouthwash, unless you have a specific problem to treat. “There is emerging evidence that mouthwash is detrimental to other areas of health, so it is best avoided unless it has been prescribed to treat a specific oral health issue,” she says.

“Mouthwashes are not the answer to problems – unlike the adverts would make you believe – and are not a replacement of correct oral hygiene habits, like toothbrushing and interdental cleaning,” Dr Crawford-Clarke says.

If you do use mouthwash, don’t do it straight after brushing, as that rinses off toothpaste, which is better for your teeth, he says.

“Using it after meals or at another time of brushing is much better, if you want to add it into your oral hygiene routine,” Dr Crawford-Clarke says. “If you are concerned about the alcohol content then I would find one that is alcohol free.”

Alternatives include sugar-free gum or mints or using a tongue scraper, he adds.

A Listerine spokesperson said: “Studies on the impact of Listerine on oral health have been published in hundreds of peer-reviewed publications for more than a century, making it one of the most extensively tested oral mouthwash brands in the world. We continuously evaluate the latest science. There is no evidence that Listerine causes cancer.”

Fastest ways to freshen your breath

• Chew sugar-free gum: stimulates saliva production, which protects teeth

• Drinking water: keeps the mouth hydrated and helps rinse away debris after meals

• Eat beetroot and spinach: vegetables high in nitrate (a prebiotic) help balance “good” and “bad” bacteria in the mouth and reduces acidity

• Brush and floss regularly: removes plaque and food particles that cause bad breath