Ever since 1819, when a New Orleans dentist named Levi Spear Parmly began recommending his patients run a waxen silk thread between their teeth, flossing has been a topic of interest for oral health experts. However, given the lack of large studies surrounding the dental cleaning technique, there’s been great debate over it over the years.
“I think this whole debate or controversy stems from the fact that there really haven’t been good studies that prove the use of floss,” says dentist, Dr. Frank Scannapieco, who’s also chair and professor of oral biology in the University at Buffalo School of Dental Medicine. “It’s not like there’s proof it doesn’t work, there just haven’t been rigorous studies showing that it works.”
Regardless, less than half of all Americans floss daily, according to a CDC survey. Dental experts still want to see more people adopt the habit. Here’s what to know about the debate over flossing.
The evidence
The number of studies on flossing are limited. In 2011, the Cochrane Collaboration, a group of researchers that analyzes studies to answer health questions, conducted a review of the evidence on flossing. They looked at 12 studies and found that there was only weak evidence that flossing could reduce plaque. In 2019, a follow-up review found that the evidence in favor of flossing was minimal.
In 2015, flossing took another hit when the United States Dietary Guidelines for Americans, published every five years, didn’t include flossing in its list of recommendations as it had in years prior. The following year, the Associated Press examined 25 studies on flossing and published an article claiming there was no scientific evidence for flossing.
“The research tells us that contrary to traditional belief, flossing is the worst interdental cleaning method available,” says Georgios Kotsakis, an associate professor in the periodontics department of the University of Texas at San Antonio. He adds that only toothpicks are worse than floss when it comes to cleaning between teeth.
But some experts point out that these studies have their flaws. For one, they ask participants to self-report how much they floss, which could yield unreliable data: One poll found that one out of four people lie about their flossing habits. Plus, people’s flossing techniques and preferences vary significantly. Two people might floss, but one person’s flossing might be effective while another person’s technique is not.
Will there ever be a gold standard study to definitively show that flossing works? It’s unlikely, Scannapieco says. Floss, like toothbrushes and a whole host of other products we use every day, might be too embedded in our culture to get studied at length. Flossing originated over 200 years ago, before scientists began using randomized clinical trials to assess the effectiveness of medical treatments.
“There also haven’t really been good studies to prove the value of the toothbrush, but that doesn’t mean that doesn’t work,” Scannapieco says.
Most clinical trials today also tend to receive funding from companies with a vested interest in learning whether a product works, and many people already assume flossing and toothbrushing are effective.
“A lot of the impetus for studying a product is whether or not a company can make money on it,” Scannapieco says. “I don’t think companies are out to prove whether or not floss works because they won’t recoup the cost of running a big trial.”
The takeaway
So should we listen to the research telling us to throw out our floss? Not so fast, dentists say.
“Flossing improves oral hygiene when added to toothbrushing alone,” Kotsakis says. But for a bigger boost to oral health, he suggests incorporating tools beyond flossing. “Alternatives such as waterjets and interdental brushes help reduce inflammation much better.”
For patients who struggle with flossing—whether they find it difficult and time consuming, or their teeth are too crowded to easily floss between them—Kotsakis also recommends those alternatives, along with other oral irrigators and dental tape. Scannapieco says it makes practical sense to clean between the teeth, and he always recommends flossing to his patients.
“Most dentists or hygienists will tell you flossing helps,” Scannapieco says. “You have to clean in between your teeth somehow.”
Scannapieco has noticed that his patients who take the time to floss correctly tend to have better gum health, less bad breath and decreased inflammation. Flossing to remove bacteria at the gum line could reduce the risk of gum inflammation and ultimately prevent plaque from forming.
“If you were to do a well-designed, large scale, placebo-controlled clinical trial, it would show that floss has benefits,” Scannapieco says. “Maybe someday somebody will do that study to correct this misunderstanding.”