Floss once a day. That is the recommendation of the American Dental Association and every major dental body, and the reasoning is simple: a toothbrush cleans three of a tooth’s five surfaces, and the two surfaces that touch neighbouring teeth, about a third of the tooth, are where a large share of cavities and nearly all gum disease begins. Cleaning between the teeth once a day, with string floss, a water flosser, or interdental brushes, is what reaches them. Timing matters less than consistency; before bed is the most useful slot.
Why brushing isn’t enough
A tooth has five surfaces: the outside, the inside, the top, and the two sides that touch the teeth next to it. Toothbrush bristles cannot reach the sides where teeth contact. Plaque grows there undisturbed, hardens into tartar within a few days, and the gum between the teeth, which is the most delicate gum tissue in the mouth, is the first to become inflamed. That is why gums bleed on flossing before they bleed on brushing, and why cavities between teeth are so common and so hard to see until they are large.
What the evidence actually says
In 2016 a widely shared news story reported that the US government had dropped flossing from its dietary guidelines and that the evidence for it was weak. Both were technically true and widely misread. The guidelines dropped it because they had never been meant to cover dental hygiene, and the “weak evidence” referred to the quality of the trials, which were short, small, and often studied flossing done badly, not to any finding that flossing fails.
What the research shows, from a Cochrane review updated in 2019 and later work:
- Flossing plus brushing reduces gum inflammation compared with brushing alone, consistently across trials.
- Interdental brushes are at least as effective as floss and probably better where they fit, especially for the back teeth.
- Water flossers reduce gum bleeding at least as well as string floss in several trials, and are clearly better for people with braces, implants, or bridges.
- Evidence on cavities between teeth is thinner because cavities take years to develop and trials last months. Population data and the biology both point the same way.
Every professional body, having reviewed the same data, recommends daily interdental cleaning. The honest summary is that the evidence for gum health is solid and the evidence for cavity prevention is likely but under-studied.
How often
Once a day is the standard. The plaque between teeth takes about 24 hours to mature into the inflammatory form that damages gums, so a daily disruption keeps it from getting there. Twice a day is fine if you enjoy it or have gum disease. Every other day is much better than never but lets plaque begin to harden. Once a week is closer to never than to daily.
Consistency beats intensity. A quick, thorough floss every night beats a heroic session on Sundays.
When
Before bed is the best single slot. Saliva flow drops during sleep, so whatever is left between the teeth overnight does the most damage. Floss, then brush, so the fluoride reaches the surfaces you just cleared (some studies find floss-then-brush removes slightly more plaque than the reverse; either order is acceptable).
If evenings never happen, morning flossing is fine. The point is once a day at a time you will actually do it.
What to use
String floss. Cheapest and most precise. Waxed slides more easily between tight contacts; unwaxed is thinner. Wrap around the middle fingers, guide with thumbs and index fingers, curve into a C around each tooth and slide gently below the gum line. Use a clean section for each gap.
Floss picks. A plastic handle with a short strand. Easier for many people, especially with the back teeth. Less effective than string because you cannot curve the floss around the tooth, but far better than nothing.
Interdental brushes. Tiny bottle brushes in sizes from 0.4 mm up. Best option wherever there is space between teeth to fit one, which is most adults’ back teeth and anyone with gum recession. Use the largest size that fits without forcing.
Water flossers. A pulsating jet of water. Excellent for braces, implants, bridges, limited dexterity, and people who simply will not use string. Our water flosser guide covers how they compare, and Waterpik vs floss asks whether one can replace the other.
Soft picks and rubber-tipped picks. Gentle, useful for tender gums, less thorough.
Use whichever one you will use every day. That is the entire criterion.
If your gums bleed
They will, for the first week or two, if they have not been flossed regularly. Bleeding means the gum between the teeth is inflamed because plaque has been sitting there. Keep going gently; it stops as the inflammation clears. Bleeding that continues past two to three weeks of daily flossing means tartar below the gum line or periodontitis, and needs a cleaning. Our bleeding gums guide explains what to look for.
When to see a dentist
See a dentist if gums bleed for more than two to three weeks despite daily flossing; if floss catches, shreds, or snaps on a particular tooth, which can mean a cavity, a rough filling, or tartar; if there is a bad smell or taste from one specific gap; if a gap between two teeth has opened up or food packs there constantly; or if you have not had a professional cleaning in a year. Ask the hygienist to show you where you are missing; most people have one or two spots they never reach.
Frequently asked questions
Is it OK to floss only once a day?
Yes, once a day is the standard recommendation and enough to prevent plaque between the teeth from maturing. More often is fine but not necessary.
Should I floss before or after brushing?
Either order works. Flossing first has a slight edge in some studies because it lets the toothpaste’s fluoride reach between the teeth afterward. Choose whichever makes you more likely to do both.
Is a water flosser as good as flossing?
For gum health, trials show water flossers reduce bleeding and inflammation at least as well as string floss, and they are better for braces, implants, and bridges. Some dentists still recommend string floss for tight contacts. Either beats nothing.
Is it too late to start flossing?
No. Gums that bleed at first will settle within a couple of weeks of daily flossing. Gum disease that has already caused bone loss cannot be reversed, but flossing stops it getting worse.
Why does floss shred between two of my teeth?
Usually a rough edge on a filling, a chipped tooth, tartar, or a cavity. Have a dentist look at that spot.
