Skipping floss lets bacteria colonize the tight spaces between your teeth where toothbrush bristles can’t reach. Over time, this leads to inflamed gums, cavities between teeth, persistent bad breath, and eventually irreversible bone loss. About 4 in 10 U.S. adults over 30 already have some level of gum disease, and that number climbs to 60% for adults 65 and older.
What Builds Up Between Your Teeth
Within hours of eating, a sticky film of bacteria called plaque begins forming on every surface of your teeth. Pioneer species like Streptococcus and Actinomyces attach first, then start consuming oxygen in the gaps between teeth. This creates low-oxygen pockets that allow more aggressive, disease-causing bacteria to move in. One of the worst offenders, Porphyromonas gingivalis, thrives in these oxygen-depleted spaces and is directly linked to gum disease.
A toothbrush cleans the front, back, and chewing surfaces of your teeth effectively. But the sides of your teeth, where they press against each other, stay untouched. That’s roughly 35% of your total tooth surface area. Without some form of interdental cleaning, plaque in those areas matures and hardens into tartar, which can only be removed professionally.
Gum Disease Starts Quietly
The first thing that happens when plaque sits undisturbed between your teeth is gingivitis: your gums become red, swollen, and bleed when you brush. Many people assume bleeding gums are normal. They’re not. Bleeding is a sign your immune system is actively fighting a bacterial infection along the gumline.
The good news is that gingivitis is fully reversible. With consistent cleaning, including between your teeth, inflamed gums can return to a healthy state in about two weeks. But if you ignore it, gingivitis can progress to periodontitis, and that’s a different situation entirely.
In periodontitis, the gums begin pulling away from the teeth, forming deep pockets that can reach a centimeter or more. Bacteria colonize these pockets, and your body’s inflammatory response starts breaking down the bone that holds your teeth in place. This bone loss is permanent. Periodontitis progresses in episodes: short bursts of tissue destruction followed by quieter periods where things stabilize or even improve slightly. But it never resolves on its own. Over time, teeth shift position, become loose, hurt when you chew, and can eventually fall out.
Cavities Form Where You Can’t See Them
Cavities between teeth, called interproximal cavities, are among the most common types dentists find. They develop on the hidden contact surfaces where plaque sits undisturbed, and they’re often invisible until they show up on an X-ray or cause pain. A systematic review from the National Institutes of Health found that professionally flossed teeth had a roughly 14 to 21% lower risk of developing cavities on those surfaces compared to unflossed teeth. Interestingly, self-performed flossing in the studies reviewed showed no statistically significant cavity reduction, likely because most people don’t floss with proper technique. The tool works, but only if it’s used well.
Chronic Bad Breath
That lingering bad breath that doesn’t go away after brushing often originates from bacteria trapped between teeth. Anaerobic bacteria, particularly Porphyromonas species, break down sulfur-containing amino acids in food debris and produce volatile sulfur compounds: hydrogen sulfide (the rotten egg smell) and methyl mercaptan (which smells like decaying cabbage). Methyl mercaptan is considered the most harmful of these compounds, not just to your social life but to your gum tissue itself. These sulfur byproducts actively damage periodontal tissue, creating a cycle where the bacteria both cause the smell and worsen the disease.
Mouthwash can temporarily mask this, but if the bacterial colonies between your teeth remain undisturbed, the odor returns within hours.
Effects Beyond Your Mouth
Chronic gum inflammation doesn’t stay contained to your gums. When bacteria like P. gingivalis enter the bloodstream through inflamed gum tissue, they can trigger immune responses elsewhere in the body. One well-studied mechanism involves a protein on the surface of these bacteria that closely resembles a human protein found in blood vessel walls. Your immune system, primed to attack the bacterial version, can cross-react with the human version, fueling chronic inflammation inside arterial walls. This promotes the buildup of cholesterol-laden plaque in arteries, narrowing them and raising the risk of heart attacks and strokes.
The relationship between gum disease and diabetes runs in both directions. High blood sugar creates conditions in the mouth that favor harmful bacterial shifts, and the chronic inflammation from gum disease makes blood sugar harder to control. Researchers have also identified associations between oral bacteria and gastrointestinal conditions, neurological conditions, and certain cancers, though the exact mechanisms for many of these links are still being mapped.
What Treatment Looks Like (and Costs)
If gum disease progresses beyond what regular cleanings can manage, your dentist will likely recommend scaling and root planing, commonly called a deep cleaning. This involves going below the gumline to scrape away tartar and smooth the tooth root surfaces so gums can reattach. The procedure is done in quadrants (your mouth is divided into four sections), and each quadrant typically costs between $198 and $272. A full mouth deep cleaning can run $800 to $1,100 before insurance. For comparison, a spool of floss costs a few dollars and lasts a month.
Treatment at this stage aims to stop the disease from getting worse. It can’t regenerate bone that’s already been lost.
Interdental Brushes May Work Better
If you find string floss difficult or uncomfortable, interdental brushes are a strong alternative. A consensus statement from the European Federation of Periodontology identified interdental brushes as the most effective method for removing plaque between teeth, consistently outperforming both floss and wooden picks. Studies in patients with gum disease found that interdental brushes removed more plaque and achieved greater pocket depth reduction than floss. In people with healthy gums, interdental brushes and rubber-tipped picks both reduced plaque scores when added to toothbrushing, while floss as an add-on showed no measurable improvement in one study.
The key factor is finding a tool that fits between your teeth and that you’ll actually use daily. For people with tightly spaced teeth, thin floss or floss picks may be the only option that fits. For those with wider gaps or any degree of gum recession, interdental brushes tend to clean more thoroughly and are easier to use correctly. Water flossers are another option, particularly for people with braces or dental work that makes traditional flossing impractical.