Flossing does help, but the evidence behind it is weaker than most people assume. A major Cochrane review of 12 studies found that flossing plus brushing reduces gum inflammation compared to brushing alone, but the effect is modest. Meanwhile, the evidence that flossing prevents cavities is “weak” and “very unreliable.” That gap between the strong recommendations you’ve heard your whole life and the actual science is what makes this question so interesting.
The short answer: cleaning between your teeth matters, but traditional string floss isn’t the only way to do it, and the benefits are smaller than decades of dental advice might suggest.
What the Research Actually Shows
The most rigorous look at flossing comes from a Cochrane systematic review that pooled data from clinical trials. People who flossed and brushed had measurably less gum inflammation than people who only brushed, and the benefit grew over time. At one month, the improvement was small. By six months, it roughly doubled. That’s a real effect, but the researchers graded the overall quality of evidence as low to very low, largely because the studies were small and short.
The evidence for plaque removal was even weaker. While flossing did reduce plaque slightly at one and three months, the reviewers called the data “very unreliable.” And for cavities specifically, there simply isn’t strong trial data showing that flossing prevents them. This doesn’t mean flossing has no effect on decay. It means no one has run the kind of long, well-controlled study that would prove it definitively. Cavity formation takes years, and getting hundreds of people to floss consistently (while a control group doesn’t) for that long is extremely difficult.
Why It Became Controversial in 2016
In 2016, the U.S. government quietly dropped flossing from its Dietary Guidelines for Americans, and the media jumped on it. The reason was straightforward: federal guidelines are supposed to be backed by scientific evidence, and the evidence for flossing didn’t meet that bar. The Associated Press investigation that followed pointed out what researchers had known for years: most flossing studies are small, short, and poorly designed.
The American Dental Association responded by reaffirming that interdental cleaning is “an essential part of taking care of your teeth and gums.” But even the ADA acknowledged the evidence challenge, framing the issue this way: when strong evidence doesn’t exist, and roughly half of Americans have some form of gum disease, even a small benefit is worth pursuing. The U.S. Department of Health and Human Services also walked back the omission, calling flossing “an important oral hygiene practice.” The takeaway wasn’t that flossing is useless. It’s that the proof is thinner than most people realized.
Why Between-Teeth Cleaning Still Matters
The biological case for cleaning between your teeth is stronger than the clinical trial data might suggest. Your toothbrush bristles can’t reach the tight spaces between teeth, and that’s exactly where bacterial film accumulates undisturbed. On exposed surfaces like your cheeks and tongue, your body naturally sheds cells and clears bacteria. Tooth surfaces don’t have that advantage. Bacteria stick, layer on top of each other, and form a structured community that hardens over time.
When this bacterial buildup sits against your gum tissue for days without disruption, it triggers inflammation. Within a few days, gums become red, swollen, and bleed more easily. Left alone longer, the bacterial community shifts. Oxygen-loving species give way to types that thrive in low-oxygen, inflamed environments, and these are the ones associated with tissue destruction. In people whose immune systems respond aggressively to this bacterial shift, the inflammation can destroy the bone supporting the teeth. That’s periodontitis, and it’s irreversible.
A meta-analysis looking at oral hygiene and periodontitis risk found that people with fair oral hygiene were about twice as likely to develop periodontitis compared to those with good hygiene. People with poor oral hygiene were five times as likely. Flossing specifically showed only a borderline, non-significant 13% reduction in periodontitis risk in the pooled data. But oral hygiene as a whole, which includes interdental cleaning, clearly makes a difference.
The Connection to Broader Health
Periodontitis isn’t just a mouth problem. The bacteria involved can enter the bloodstream, and the chronic inflammation they trigger doesn’t stay local. The link between gum disease and cardiovascular disease is one of the most studied relationships in oral medicine. Oral bacteria have been found in arterial plaques, and people with periodontitis tend to have higher levels of inflammatory markers associated with heart disease and stroke.
The relationship between gum disease and type 2 diabetes runs both directions. Diabetes makes gum disease worse, and the systemic inflammation from periodontitis can worsen blood sugar control by contributing to insulin resistance. Gum disease has also been associated with respiratory infections (particularly pneumonia), rheumatoid arthritis, chronic kidney disease, and Alzheimer’s disease. These are associations, not proven cause-and-effect relationships, but the pattern is consistent enough that preventing gum disease has implications beyond your mouth.
Alternatives to String Floss
If you find string floss difficult or unpleasant, you have options that work as well or better. Interdental brushes, those tiny bottle-brush-shaped picks, remove significantly more plaque than string floss in head-to-head comparisons. One study found they also produced greater reductions in gum pocket depth. People in these trials consistently reported finding interdental brushes easier to use, which matters because a tool you actually use beats one you don’t.
Interdental brushes work best when there’s enough space between teeth to fit the brush. For very tight contacts, string floss or thin picks may be the only option. The key is matching the tool to the gap.
Water flossers are another popular alternative. Clinical trials comparing water flossers to string floss generally show similar outcomes for plaque and bleeding reduction. Some shorter studies have found water flossers slightly better at reducing gum bleeding, though longer trials show the difference isn’t statistically significant. Water flossers can be especially useful for people with braces, dental implants, or dexterity issues that make string floss impractical.
Technique Matters More Than the Tool
Most of the benefit from flossing depends on doing it correctly, and most people don’t. Simply snapping floss between your teeth and pulling it back out barely disrupts the bacterial film sitting along the gum line. The effective method involves curving the floss into a C shape against each tooth surface once it reaches the gum line, then rubbing up and down to physically scrape the bacterial layer off. Each tooth has two sides, so each gap between teeth requires two C-shaped passes.
This is one reason the clinical evidence looks underwhelming. In studies, participants are asked to floss, but how thoroughly they actually do it varies enormously. Professional cleanings in a dental office show dramatic plaque reduction because the technique is precise. Home flossing is messier, and the gap between ideal and actual technique likely explains some of the modest results in trials.
If you’ve been skipping flossing entirely, starting with any interdental cleaning method, done gently and consistently, is more important than choosing the “perfect” tool. Once-daily cleaning between teeth, paired with twice-daily brushing, is what the ADA recommends. The goal is simple: don’t let bacterial communities sit undisturbed against your gums long enough to cause problems.