Despite everything your dentist has ever told you, there’s not all that much scientific evidence that supports daily flossing, a major investigation by the Associated Press finds. 

“The AP looked at the most rigorous research conducted over the past decade, focusing on 25 studies that generally compared the use of a toothbrush with the combination of toothbrushes and floss. The findings? The evidence for flossing is ‘weak, very unreliable,’ of ‘very low’ quality, and carries ‘a moderate to large potential for bias,’” the news service reports. 

The American Dental Association and the American Academy of Periodontology have both asserted that flossing is an essential part of dental hygiene. But the studies they cite to back up this claim, the AP says, are marred by major design flaws, including outdated methods, small samples, or short time frames. (Some studies, for example, lasted just two weeks—which is not enough time for a cavity or dental disease to develop, the AP points out.) And many studies on flossing are designed and paid for by the companies that sell floss, like Procter & Gamble and Johnson & Johnson. Industry-funded research findings can be legitimate, but when a private company is designing and paying for studies, there are many opportunities to bias the results in favor of the corporation’s bottom line. 

This is a potential problem in many health-related industries, including pharmaceuticals, as The Washington Post argued in 2012:

“Company executives seeking to promote their drugs can design research that makes their products look better. They can select like-minded academics to perform the work. And they can run the statistics in ways that make their own drugs look better than they are. If troubling signs about a drug arise, they can steer clear of further exploration.”

Nutrition studies funded by the sugar industry, for instance, tend to gloss over the major health risks associated with sugar, and only last year, Coca-Cola and other beverage companies sponsored a study that found that drinking diet soda was more beneficial to weight loss than water. While Procter & Gamble may have a stake in finding the best ways to keep your teeth healthy, the company also benefits if you buy more of those little plastic floss picks it sells, regardless of whether you need them or not. 

This year the U.S. government dropped flossing from its dietary guidelines for the first time since it was included in 1979. The government told the AP that its effectiveness had not been researched, which is required by law for inclusion in the guidelines.  

Flossing is a relatively low-cost, low-risk activity for the average dental patient, so it’s not particularly surprising that more dentists haven’t come out against it. But that doesn’t necessarily mean it’s necessary.   

Read more about it from the AP.

Know of something you think we should cover? Email us at tips@mentalfloss.com.