It’s one of the most universal recommendations in all of public health: floss daily to prevent gum disease and cavities.

Except there’s little proof that flossing works.

Still, governments, dental organisations and manufacturers of floss have pushed the practice for decades. Dentists provide samples to their patients; the British Dental Association insists on its patient website that flossing helps “in the battle against tooth decay and gum disease”.

But all this could change following an investigation by Associated Press (AP). Last year journalists from the agency asked the departments of health and human services and agriculture in the US for their evidence that flossing works.

Since then, the US government has quietly dropped the recommendation, admitting that there is no scientific evidence to prove the benefits. And now the NHS is set to review their own guidelines.

On its website, it currently states that dental floss “helps to prevent gum disease by getting rid of pieces of food and plaque from between your teeth” which can cause inflammation.

A leading British dentist, however, said there is only “weak evidence” that flossing helps in this way. Professor Damien Walmsley of Birmingham University, said the time and expense required for reliable studies meant the health claims often attributed to floss were unproven.

Walmsley, who is also a scientific adviser to the British Dental Association, said: “The difficulty is trying to get good evidence. People are different and large studies are costly to do ... until then you can’t really say yes or no.”

He added “more sophisticated trials” were needed. “It’s important to tell people to do the basics. Flossing is not part of the basics.”

AP also looked at the most rigorous research of the past decade. Twenty-five studies in leading journals found evidence for flossing is “weak, very unreliable”, of “very low” quality, and carries “a moderate to large potential for bias”.

One review conducted last year said: “The majority of available studies fail to demonstrate that flossing is generally effective in plaque removal.”

Another 2015 review cites “inconsistent/weak evidence” for flossing and a “lack of efficacy”. One study did credit floss with a slight reduction in gum inflammation. However, the reviewers ranked the evidence as “very unreliable”. A commentary in a dental magazine stated that any benefit would be so minute it might not be noticed by users.

A major review last year concluded: “The majority of available studies fail to demonstrate that flossing is generally effective in plaque removal.”



Procter & Gamble, which markets several brands of the product and claims that its floss fights plaque and gingivitis, pointed to a two-week study, which was discounted as irrelevant in the 2011 research review. Johnson & Johnson spokesman Marc Boston said floss helpsed remove plaque. When the AP sent him a list of contradicting studies, he declined to comment.

A Public Health England (PHE) spokeswoman said it keeps “abreast of the evidence base and will consider these findings”.

She said: “Some people may not have large enough spaces in between their teeth to use an inter-dental brush, so flossing can be a useful alternative. Patients should speak to their dentist if they have any concerns.”

Floss can occasionally cause harm, with poor technique leading to damaged gums and teeth and also dislodging bad bacteria, which can lead to infections.

The British Dental Association said: “Small inter-dental brushes are best for cleaning the area in between the teeth, where there is space to do so. Floss is of little value unless the spaces between your teeth are too tight for the interdental brushes to fit without hurting or causing harm.”

Dentist Levi Spear Parmly is credited with inventing floss in the early 19th century. By the time the first floss patent was issued, in 1874, the applicant noted that dentists were widely recommending its use.