Is flossing still necessary in 2026, or can you skip it?

The 2016 Associated Press investigation found "weak evidence" for flossing and the US government quietly removed it from dietary guidelines. So is it actually useless? The honest answer requires understanding what the research actually said, and what dentists see every day.

In August 2016, an Associated Press investigation set off a small earthquake in dentistry. After a year-long Freedom of Information request, the AP reported that the United States government had quietly removed flossing from the Dietary Guidelines for Americans without ever producing the kind of evidence required to keep it in. The headline that went around the world was that flossing did not work. Patients told their dentists. Dentists, for the most part, told their patients to keep flossing anyway. Almost a decade later, the question still surfaces in every other hygiene appointment: does this thing actually do anything?

The short answer is yes, but not for the reason most people assume, and not in the way many people are doing it. The longer answer requires walking through what the 2016 review actually concluded, what mechanistic and clinical research has shown since, how water flossing compares, and where the genuine uncertainties remain. This piece does exactly that. By the end, you should have a clear sense of whether you can skip the floss, replace it, or whether you simply need to do it better.

The 2016 AP investigation: what it actually said

The AP story began with a paperwork question. Each cycle of the Dietary Guidelines for Americans is supposed to be supported by a documented evidence review. Flossing had been recommended in those guidelines since 1979. When the AP asked the US Department of Health and Human Services to produce the evidence review for the flossing recommendation, the answer came back that no such review existed. The recommendation had not been formally re-evaluated in years. In late 2015, the government quietly dropped flossing from the next edition of the guidelines. The AP then did its own scan of the published literature on flossing for cavity and gum disease prevention. It identified 25 studies of varying quality and concluded that the evidence base was, in the words of the investigation, "weak, very unreliable, of very low quality, and biased."

That phrasing is important because it was not a statement about whether flossing works. It was a statement about the methodological quality of the trials that had been published. Most of the studies were small, with under 100 participants. Many were short, lasting only a few weeks. Almost none were properly blinded, which is essentially impossible to do well for a hygiene behaviour. A great many were funded or coauthored by floss manufacturers. And the outcomes were inconsistent, with some studies showing a clear plaque or bleeding reduction and others showing little difference between flossers and non-flossers.

The most cited authority within the AP piece was a 2011 Cochrane review by Sambunjak and colleagues titled "Flossing for the management of periodontal diseases and dental caries in adults." That review pooled 12 trials covering just over 580 participants in trials of flossing plus brushing versus brushing alone. The reviewers concluded that there was some evidence that flossing in addition to brushing modestly reduces gingivitis compared with brushing alone, with the quality of the evidence rated low to moderate. For caries specifically, the reviewers could not find enough good-quality evidence to conclude that flossing prevents cavities. That language, repeated in news headlines, became the public memory of the entire issue.

The crucial nuance the headlines flattened is that the absence of strong randomized controlled trial evidence is not the same thing as evidence of absence. In clinical research methodology, those are very different statements. A trial can fail to detect an effect because the effect does not exist, or because the trial was too small, too short, or too noisy to detect it. The 2016 AP review and the Cochrane review both concluded the second of those, not the first. They said the trials were not good enough to be sure flossing helps, not that the trials had shown flossing does not help. The American Dental Association, the American Academy of Periodontology, and the original Cochrane authors all publicly clarified this distinction in the weeks following the AP story. None of them reversed their recommendation.

The mechanistic case for flossing

If the randomized trial evidence is thin, the mechanistic case is overwhelming. A toothbrush, even an electric one with a small precision head, cannot physically reach the interproximal surfaces between adjacent teeth. The bristles approach the tooth from the buccal (cheek) or lingual (tongue) side, and they slide over the contact point between teeth without contacting the flat surfaces on either side of it. Those flat surfaces represent roughly 35 to 40 percent of the total tooth surface area in a normal adult dentition. They are the single largest area of tooth that a toothbrush is geometrically incapable of cleaning.

This is not a controversial claim. It is observable in any dental practice with disclosing solution, the dye used to highlight dental plaque. After a careful two-minute brushing session, the buccal and lingual surfaces light up only faintly. The interproximal surfaces, particularly the ones near the gumline, light up brightly. The plaque that brushing did not remove is sitting in exactly the place where the toothbrush could not reach. That is what flossing, interdental brushing, or water flossing exists to address. The geometric problem is real and is not solved by spending longer with the brush or buying a better brush.

The other piece of the mechanistic case concerns the biology of the subgingival biofilm, the plaque that develops just below the gumline in the small pocket between the tooth and the gum tissue. That pocket is anaerobic, low oxygen, and rich in serum proteins leaking from the surrounding tissue. It is the preferred niche of the most pathogenic bacteria associated with periodontitis: Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola, and the bridging species Fusobacterium nucleatum. A toothbrush cannot reach this pocket. Floss, properly used by sliding gently below the gumline and hugging the tooth on each side of the contact, physically disrupts the biofilm there. That disruption is the mechanism by which interdental cleaning influences periodontal disease.

Research published in the Journal of Clinical Periodontology in the late 2010s used scanning electron microscopy to confirm what dentists have long observed. Subgingival biofilms in unflossed interdental spaces become structurally mature within roughly 48 to 72 hours of undisturbed growth. The biofilm develops a polysaccharide matrix that protects the inner bacteria from saliva, immune cells, and antimicrobial molecules. Once mature, only mechanical disruption, scaling at a dental visit, or chemical antiseptics with prolonged contact times can break it apart. Brushing the outside of the tooth has essentially no effect on it. This is the precise biological reason interdental cleaning is recommended once a day rather than once a week. The 24 hour interval is short enough to keep the biofilm immature.

What periodontal research shows

The 2011 Cochrane review on flossing did not stand alone for long. In 2019, a much broader Cochrane review by Worthington and colleagues, titled "Home use of interdental cleaning devices for the prevention and control of periodontal diseases and dental caries," pooled 35 trials with over 3,900 participants. It was the largest synthesis of interdental cleaning evidence ever published. The conclusions were notably more confident than the 2011 version. Interdental brushes (the small bottle-brush style tools) were ranked highest for reducing both gingival inflammation and bleeding on probing. Flossing was ranked second. Water flossing was ranked close to flossing on both endpoints. All three were superior to brushing alone.

The headline reduction in gingival bleeding from regular interdental cleaning across the pooled trials was roughly 30 to 35 percent compared with brushing alone over follow-up periods of one to six months. The corresponding reduction in interproximal plaque scores was in a similar range. For people with established gingivitis at baseline, the effect sizes were larger. For people with healthy gums and minimal baseline bleeding, the effect sizes were smaller, simply because there was less room to improve. Either way, the direction of effect was consistent across nearly every trial included.

The clinical relevance of those numbers is not trivial. Gingival bleeding on probing is the most reliable early sign of gingivitis, which if left to progress becomes periodontitis, the leading cause of tooth loss in adults over the age of 40. The Journal of Dental Research has published several long-term cohort studies showing that adults with consistent interdental cleaning habits have lower lifetime rates of periodontitis and tooth loss compared with adults who only brush. The effect is not enormous, but it is consistent, and it accumulates over decades.

On caries specifically, the picture is more uncertain. Cavities forming between teeth (interproximal caries) are a major share of adult tooth decay, and the geometric argument suggests interdental cleaning should help prevent them. The trial evidence is mixed, partly because the cariogenic process takes years to produce a visible cavity and most flossing trials are far too short to capture that timeline. A small Norwegian study published in the late 1980s, often cited as the strongest single trial of flossing for caries, showed a meaningful reduction in interproximal cavities in school-age children when professional flossing was performed daily by trained dental staff over two years. That same effect was not reproduced in trials that relied on participants flossing themselves at home, which probably says more about adherence and technique than about the biology.

Water flossing vs string flossing vs interdental brushes

If interdental cleaning is what matters and string floss is one of three options to achieve it, the natural next question is which option is best. The honest answer is that the three options have different strengths and the right choice depends on the mouth and on the patient. Below is the practical comparison that emerges from the 2019 Cochrane review, the 2022 International Journal of Dental Hygiene systematic review on water flossing, and from clinical practice patterns across periodontal practices.

The single most important pattern in this table is the adherence column. The 2022 International Journal of Dental Hygiene review noted that daily compliance with string flossing in self-reported and electronically monitored studies sits stubbornly between 20 and 30 percent of users, even among people who say they intend to floss daily. Water flossers, in the same population samples, sit closer to 60 percent. The reason is not biological superiority; it is that the action is faster, more comfortable, and easier to make habitual. A method with moderate per-session efficacy and high adherence beats a method with high per-session efficacy and low adherence over any timescale longer than a few weeks.

Interdental brushes are the dark horse of the comparison. In mouths where the gum papilla between teeth has shrunk enough to leave a visible triangle of space (which happens after age 40 in many people, or earlier in people with periodontal history), an interdental brush is the highest-efficacy option per stroke. It physically wipes the curved interproximal surfaces in a way that neither floss nor a water jet can quite match. The catch is that the brush must actually fit. In a young, healthy mouth with tight contacts and full papilla, an interdental brush cannot squeeze in. This is why the recommendation evolves with age. In your twenties, string floss or water; in your fifties, interdental brushes are often the better daily tool.

Who needs to floss the most

The general recommendation to floss once a day is fine as a baseline, but the marginal benefit of interdental cleaning is not uniform across the population. Some mouths gain a great deal from daily flossing. Others gain comparatively little. Understanding which category you are in is the difference between thinking of flossing as a small chore and thinking of it as a meaningful protective behaviour.

Tight contacts and crowded teeth

If your teeth are tightly aligned, with closed contact points and no visible space between adjacent crowns, the inside of those contacts is essentially inaccessible to anything except floss. Saliva does not flow through them. Brush bristles do not reach them. A water flosser sweeps across them rather than between them. Food debris and bacterial biofilm accumulate in the tiny anaerobic space below the contact. People with naturally well-aligned dentitions are often the most cavity-prone in this exact location, because the protective force of saliva flow cannot intervene. For these mouths, string floss is the highest-leverage tool. Substituting it with a water flosser alone leaves a meaningful gap.

Periodontal history and chronic gingivitis

Anyone with a history of periodontal disease, even if it has been stabilized, sits in the high-yield category for interdental cleaning. The same subgingival pockets that previously harbored P. gingivalis and its anaerobic companions remain anatomically deeper than in a never-affected mouth. They are predisposed to recurrence. Daily mechanical disruption of those pockets is one of the few patient-level behaviours with consistent evidence for reducing the rate of periodontal relapse. The Journal of Clinical Periodontology has reported that periodontal maintenance outcomes correlate strongly with patient interdental cleaning adherence over five and ten year horizons.

Implants, bridges, and dental work

A dental implant is a titanium fixture that integrates with the jawbone and supports a crown. It does not have the same protective biology as a natural tooth. There is no periodontal ligament. There is no cementum to anchor connective tissue. The seal between the implant and the surrounding gum is, biologically, more fragile than the seal around a natural root. Peri-implantitis, the implant equivalent of periodontitis, develops faster and is more destructive when biofilm accumulates around the implant neck. Interdental cleaning around implants is therefore not optional. Water flossing and interdental brushes (typically with plastic-coated wire to avoid scratching the titanium) are the preferred tools. Standard string floss can sometimes shred fibers below the gumline, which is why it is the third choice rather than the first around implants.

Diabetes, smoking, and immunocompromised states

Several systemic conditions amplify the impact of interdental biofilm. Type 2 diabetes raises gingival inflammation and reduces tissue healing capacity, and is one of the strongest non-behavioural risk factors for periodontitis. Smoking suppresses the immune response in gum tissue and masks bleeding, which lets disease progress further before symptoms appear. Pregnancy, particularly the second and third trimesters, shifts immune and hormonal balance in ways that produce more bleeding and inflammation for the same level of biofilm. People with HIV, autoimmune disease, or who take immunosuppressive medications run similar risks. In each of these groups, the absolute benefit of daily interdental cleaning is larger than in a baseline-healthy adult, because the underlying tissue has less reserve to absorb the inflammatory load of an undisturbed biofilm.

Common flossing mistakes

A surprising fraction of the people who say they floss are doing it in a way that delivers a fraction of the possible benefit and a non-trivial amount of harm. Hygiene appointments routinely surface the same handful of technique errors, and it is worth listing them explicitly because most of them are easy to correct in a few seconds at the bathroom mirror.

Sawing back and forth across the gum papilla

The single most common mistake is treating floss like dental string for a saw. The user pulls the floss into the contact and then drags it horizontally back and forth, scrubbing through and over the small triangle of gum tissue between the teeth. This cuts the papilla. It also fails to clean the actual interproximal surfaces effectively, because the floss is moving across the contact rather than against either of the two flat tooth surfaces that need cleaning. Over years, the chronic micro-trauma can produce loss of the papilla and visible black triangles between the teeth. The correction is to ease the floss past the contact with a gentle wiggle, then change direction so the floss makes a C-shape against one tooth, slides up and down it, then re-curves against the other tooth before lifting out.

Snapping through tight contacts

When a contact is very tight, many people apply firm pressure straight down on the floss, which suddenly releases and snaps the floss into the gum tissue below. Each snap is a small injury to the connective tissue at the base of the papilla. Repeated daily, those small injuries accumulate. The fix is to use floss with a smooth coating, such as PTFE-based products, and to ease through tight contacts with a gentle wiggle from side to side rather than a downward push. If a contact is so tight that no floss can pass, an interdental brush of the appropriate size or a water flosser jet is a better option than forcing the issue.

Missing the back of the most posterior molars

The distal (back-facing) surface of the most posterior molar is not adjacent to any other tooth. There is no contact to floss between, and yet the surface still needs cleaning because biofilm accumulates there. Almost no one cleans it. The technique is to bring the floss against the back of that last molar, wrap it around to form a C-shape against the distal surface, and gently slide it up and down. The same applies to the back of any tooth standing at the end of a row (for instance, behind an implant, or beside a missing-tooth gap). These are statistically among the most undercleaned tooth surfaces in the mouth and a disproportionate source of late-life decay and pocket formation.

Stopping at the contact instead of going subgingival

Many casual flossers slide the floss into the contact, pull it back out, and consider the job done. This cleans the contact point itself, which is generally not where disease starts. The biofilm that drives gingivitis and periodontitis sits just below the gumline, in the sulcus. The floss has to make a gentle dip into that sulcus, hugging the tooth, before being lifted out. A small amount of resistance from the gum tissue is normal. Sharp pain or bright red bleeding is not. Bleeding for the first one to two weeks after starting daily flossing is common and is usually a sign of pre-existing gingivitis resolving rather than of new injury. Bleeding that persists beyond three to four weeks should be discussed with a dentist.

Using the same one inch of floss for every gap

If the same short section of floss is used for every interdental space, it transports biofilm from one site to the next. This partly defeats the purpose. The standard recommendation is to start with about 45 cm (18 inches) of floss, wrap most of it around the middle fingers, and advance fresh floss into the working zone between thumb and index finger after every two or three teeth. This is also why pre-strung floss picks, while convenient, are a compromise. They are useful in some hands and far better than not flossing at all, but the same small loop of floss is doing the work for every gap.

The minimum effective dose

A practical question that does not always get asked directly is how much flossing is actually enough. Once a day is the standard recommendation, but the underlying biology supports a more flexible reading of the rule. The subgingival biofilm needs roughly 24 to 48 hours to mature into a structure that drives inflammation. As long as the biofilm is disrupted within that window, the inflammatory cycle does not get a chance to escalate. This means that flossing every other day, done properly and thoroughly, is biologically much closer to daily flossing than to no flossing. Twice a day, by contrast, adds essentially nothing on the bleeding and inflammation endpoints, while incrementally raising the risk of mechanical gum trauma.

The factor that matters more than frequency is technique and consistency. A two-minute floss session that includes the C-shape on both sides of every contact, a gentle subgingival dip, and attention to the back of the last molars will deliver far more benefit than a rushed thirty-second pass-through. Adherence research suggests the most predictive variable for long-term gum health is whether flossing has become an automatic part of the evening routine, not whether it is performed once or twice a day. People who tie it to a fixed trigger (immediately before brushing at night, for instance) are roughly three times more likely to still be flossing a year later compared with people who try to fit it in opportunistically during the day.

A reasonable minimum effective protocol, supported by the clinical evidence and reflecting the way the biofilm actually develops, looks like this. One unhurried interdental cleaning session per day, ideally in the evening before brushing, using whichever tool is most likely to be used consistently (string floss, water flosser, or interdental brushes depending on anatomy and preference). Allow two minutes. Cover every contact, both sides of every tooth, and the back of the most posterior molar on each side. Expect bleeding for the first two weeks if you are starting from a long gap. Reassess at the next dental visit.

Practical verdict: skip, replace, or commit

The honest summary of the evidence, almost a decade after the AP headline, is that you should not skip interdental cleaning, but you do have flexibility in how you do it. String floss is not magical; it is one of three roughly equivalent ways of disrupting the interdental biofilm that a toothbrush cannot reach. What matters is that something cleans those surfaces every 24 to 48 hours, and that whatever you choose is something you will actually do consistently for years.

The 2016 headline was not wrong that the formal evidence behind the federal flossing recommendation was thinner than it should have been. It was wrong about what to do with that finding. The right response was to fund better trials and to tighten public language about evidence strength. The wrong response was to throw away a daily behaviour with overwhelming mechanistic support and consistent if imperfect clinical signal. Almost a decade later, the verdict from the people who actually look inside mouths every day is unchanged. Clean between your teeth, with whatever tool you will actually use. Skipping it remains the wrong call.

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