Not cleaning between your teeth

There is a Cochrane systematic review of this exact question, which is more than most everyday health advice can claim. It gathered 35 randomised trials in 3,929 adults, all of whom brushed their teeth, and compared those who also cleaned between them with those who did not. Pooling the trials that ran six months, the flossing groups had lower gum-inflammation scores, by a standardised mean difference of -0.68 (95% CI -0.95 to -0.42, from 4 trials in 564 adults). At one month the pooled difference was -0.58 on an interval that only just cleared no difference at all, and at three months it was -0.33. The direction is consistent; the size is unsettled. Now the parts that keep this modest. The outcome is an index - a dentist scoring inflammation at a set of gum sites and averaging it - not a tooth saved and not a disease avoided. No trial in the review measured decay between the teeth, and most did not measure gum disease proper. Nobody can be blinded to whether they are flossing, so every trial carries that bias, and only two of the 35 were otherwise at low risk of bias. The reviewers graded the whole body of evidence low to very low certainty and wrote that the effect sizes observed may not be clinically important. That sentence belongs on this page as much as the number does.

Worthington HV et al. 2019

Gum disease and cardiovascular disease genuinely do keep company. In a 2023 meta-analysis of 39 cohort studies, people with periodontal disease had a 24% higher rate of major adverse cardiovascular events than people without it (RR 1.24, 95% CI 1.15 to 1.34, pooled from 17 of those studies), and the same review found higher rates of stroke, coronary heart disease, heart attack, cardiac death and death from any cause. Those are real findings and they are the reason gum disease is not a cosmetic matter. They are also, on their own, close to useless as a reason to floss, for two reasons that need stating together. The first is confounding, and here it is unusually severe. Smoking causes gum disease and causes heart disease. So does diabetes. So does poverty and everything attached to it. People with bad gums having more heart attacks is precisely what you would see even if the gums were irrelevant, because the same lives produce both. The second is the missing trial. A separate Cochrane review went looking for randomised evidence that treating gum disease prevents cardiovascular disease, searched to September 2019 in five databases, two registries, the grey literature and four Chinese-language databases, and found two trials - one with a single death in it, one too sparse to use. It concluded that the evidence was inconclusive for primary prevention and that no reliable evidence exists for secondary prevention. That is the state of the art. Anybody telling you that flossing protects your heart is telling you something no study has shown.

Guo X et al. 2023 · Liu W et al. 2019

The most common reason people give up on cleaning between their teeth is that it makes their gums bleed, which feels like proof of damage. It is worth knowing how dentistry reads the same event. Bleeding when a gum is touched is one of the standard ways gum inflammation is measured - the Cochrane review on this page records that trials assessed gingivitis both by index scores and by the proportion of gum sites that bled. A gum that is not inflamed does not generally bleed when floss passes it. So blood at a particular spot is information about that spot: it is the site telling you it has been left alone. Two honest caveats. First, the review's results for the proportion of bleeding sites were inconsistent across studies and rated very low certainty, so this page cannot put a number on how fast bleeding settles or how reliably. Second, bleeding is not always just neglect - it can accompany pregnancy, some medications including blood thinners, and several medical conditions, and gums that bleed heavily, hurt, or keep bleeding for weeks after you have started cleaning between them are a reason to see a dentist rather than to push harder. On safety the review is reassuring as far as it goes: studies that measured adverse events found no severe events caused by any of the devices, and no difference between groups in minor effects such as gum irritation.

Worthington HV et al. 2019

"Once a day" is the standard advice, and this page does not repeat it, because we went looking for the study behind it and could not find one. Here is exactly what was searched and what turned up. Across the pooled literature there is no randomised trial and no meta-analysis comparing cleaning between your teeth once a day with doing it less often, or more often. The Cochrane review's own background does describe daily mechanical removal of plaque as important for oral health, but that is a statement of general principle in its opening paragraph, not a frequency it tested - the review compared devices against toothbrushing alone and against each other, and never compared one schedule against another. What does exist on frequency is a scattering of cross-sectional surveys correlating how often people say they clean between their teeth with things like tooth loss and self-rated oral health, which cannot separate the habit from the kind of person who has it. So the frequency number is a convention, and quite possibly a sensible one, but it is not a finding, and this brand does not put conventions on screen dressed as evidence. What the trials do license is narrower and more useful: what was tested was interdental cleaning added to toothbrushing. In every trial behind the figures on this page, the control group brushed and did nothing else. So the evidence is about the pairing, which is why the fix on this page attaches the new habit to the brushing you already do rather than to a count you have to remember. Two further things this page will not tell you to do. It will not tell you to buy a powered appliance, because the pooled evidence for water jets is the weakest in the review. And it will not tell you that this protects your heart, because the review that went looking for that evidence found two trials and could conclude nothing from them.

Worthington HV et al. 2019

Less than the marketing suggests, and the review's own ranking is weaker than its headline. Floss is the best-evidenced option simply because it has been studied most: 15 of the 35 trials tested it against toothbrushing alone. Interdental brushes produced the largest single number in the review - less plaque than brushing alone, standardised mean difference -1.07 (95% CI -1.51 to -0.63) - but that rests on 2 trials in 93 people and was rated low certainty, and the comparison suggesting interdental brushes beat floss was also low certainty and showed no difference for gum disease measured by pocket depth. Small wooden sticks came down to single trials with a couple of dozen participants each. Water jets were the weakest of the lot: some sign of lower gum inflammation at one month, nothing at three or six, and no reduction in bleeding sites or in plaque compared with brushing alone. Two conclusions follow, and neither of them is a shopping list. The strongest signals in this whole review belong to the two cheapest things in it. And because no device caused any severe adverse event and none differed from another on minor irritation, the deciding factor is not which is best on paper - it is which one you will actually pick up. A method you use beats a method you admire. In practice, use what you will actually use. Floss has the most trials behind it; interdental brushes did at least as well, and some people find them far easier to handle; if your hands are not steady, holders and picks do the same mechanical job. The review found no severe adverse events from any of it. Expect some bleeding at the sites that need it most, and expect it to settle as those gums calm down - though the pooled trials could not put a reliable timescale on that. If your gums bleed heavily, hurt, or are still bleeding weeks after you start, that is a dentist's question rather than a habit question.

Worthington HV et al. 2019

Nobody knows, and the honest answer is worth more than a confident one. The association is solid and repeatedly found: in a 2023 meta-analysis of 39 cohort studies, periodontal disease was associated with higher rates of major cardiovascular events, stroke, coronary heart disease, heart attack, cardiac death and death from any cause. Every one of those studies is observational. People were examined, sorted by the state of their gums, and followed - not randomly assigned. That design cannot separate the gums from everything that travels with them, and in this case what travels with them is unusually powerful: smoking, diabetes and socioeconomic disadvantage each independently cause gum disease and cardiovascular disease, so the two would appear together even if neither affected the other. The reviewers adjusted for many of these, and adjustment reduces confounding without removing it. The studies also disagreed sharply with one another, and where gum disease was identified by people reporting it themselves rather than by examination, several associations weakened or vanished. The way to settle it is to treat gum disease in a randomised trial and count cardiovascular events afterwards. A Cochrane review went looking for those trials and found two, both at high risk of bias, one with a single death in it and one too sparse to use, and could draw no conclusion. So: associated, plausibly connected, unproven. This page recommends cleaning between your teeth on the strength of what randomised trials show about gums, and on nothing else.

Neither answer fits everybody, so here is how to tell them apart. Light bleeding at the specific spots you have been skipping, settling as you keep going, is the common and expected pattern - bleeding on contact is one of the standard measures of gum inflammation, and inflamed gums are what get left alone. It is not a sign that you are doing damage, and the trials in the Cochrane review found no severe adverse events caused by any of the cleaning devices, nor any difference between groups in minor effects such as gum irritation. What does warrant a dentist: bleeding that is heavy, bleeding that hurts, gums that are swollen or receding, loose teeth, persistent bad taste or breath, or bleeding that has not settled after a few weeks of gentle daily cleaning. Any of those can indicate periodontitis, which is a diagnosis and a treatment rather than a habit, and this page is not a substitute for that. Get individual advice first if you take blood thinners or antiplatelet drugs, if you have a bleeding disorder or low platelets, if you are having cancer treatment, or if you have been told you need antibiotics before dental procedures. Bleeding gums are also common in pregnancy and are worth mentioning at an appointment. Nothing on this page is medical advice, nothing on it diagnoses anything, and nothing on it treats any condition.