Everyone knows sugar rots your teeth, and everyone is partly right.

When patients ask me what causes cavities, I tell them the candy bar they’re picturing does its damage through a middleman, acid, and on a schedule. The schedule is the part almost nobody manages. Understand the acid and the timing, and you can out-think most cavities, sweet tooth and all.

What actually causes cavities?

Acid made by mouth bacteria, hitting your enamel often enough that your saliva can’t keep up. A cavity is a bacterial infection that runs on your diet and is measured in pH.

Your mouth is home to hundreds of species. A few of them, Streptococcus mutans and its lactobacillus friends chief among them, eat fermentable carbohydrates and excrete acid as a waste product. Yes, the cavity is basically bacterial pee. I’m sorry. You’ll never unsee it.

How do cavities form?

Sugar is their favorite food. Crackers and bread break down into the same sugars in your mouth, though, and gummies are worse than chocolate because they stick.

That acid sits inside the sticky plaque layer pressed against your enamel. Enamel starts to dissolve when the pH at the tooth surface drops below about 5.5.

Minerals leach out and the surface goes chalky. If the attack continues long enough, it collapses into a hole.

The rescue crew is your saliva. It’s loaded with bicarbonate to neutralize acid, plus calcium and phosphate to push mineral back into the enamel.

Every day is a tug of war between demineralization and remineralization. You get a cavity when the acid side wins for months.

Is it how much sugar you eat, or how often?

How often, by a lot. Timing beats amount.

A researcher named Robert Stephan measured this in the 1940s, and the graph he produced still runs my practice. After you eat or drink anything with fermentable carbohydrate, plaque pH crashes within a few minutes. It stays below the danger line for roughly 20 to 40 minutes before saliva brings it back up.

The dose matters less than the number of times the curve dips. The person who drinks one large soda at lunch does less damage than the person who sips a small one across the afternoon.

A Swedish study from the 1950s known as Vipeholm showed the same thing in humans: between-meal sugar, eaten often, drove cavities far more than total sugar did.

This is why grazers, sippers and snackers fill my schedule. A granola bar at 10, an apple at 2, a handful of goldfish at 4 and a kombucha at 5 means your enamel never gets a full recovery. Mineral only leaves.

My own kitchen closes at 7:30 at night, and after that it’s water only. That one rule hands my teeth a long, quiet recovery window every single night.

Sparkling water and kombucha count too

They count even without sugar, because they carry their own acid. Plain seltzer sits around a pH of 3 to 4, and kombucha can be lower.

Straight chemical dissolution like that is called acid erosion. On teeth it looks different from a bacterial cavity (smooth, cupped surfaces instead of a soft brown hole), and it strips the same mineral.

Why do I get cavities even though I brush?

Usually because of your saliva, your enamel, or your snacking clock, and brushing can’t fix any of those on its own. Two people eating the same way can get very different results, and the difference is mostly saliva and enamel quality.

A dad once crossed his arms in my operatory and said, “We brush twice a day. I set a timer.” I believed him completely. Then his eight-year-old walked me through her afternoon: a juice box after school, crackers in the car, a granola bar at soccer and a lemonade with dinner. Their brushing was great, and her snacking clock never stopped ticking.

Mouth breathing, especially at night, dries the saliva that would otherwise rescue your pH. It’s the most overlooked cause I see.

Enamel itself varies. Genes shape how well it formed, and so did your mineral and vitamin status in childhood. That’s why Weston Price found nearly cavity-free teeth in populations eating traditional diets rich in fat-soluble vitamins.

A 2013 analysis at the University of Washington pooled older trials and found vitamin D supplementation cut cavity rates by roughly half in children.

How to stop cavities from forming

The plan follows the mechanism, which is my favorite kind of plan.

Eat in fewer windows, and drink water in between. Chew xylitol gum after meals to speed the pH rebound and starve S. mutans, which can’t digest xylitol.

When you can’t brush, swish with water or a pinch of baking soda.

At night, brush with a hydroxyapatite paste to hand your enamel the mineral it lost. NOBS toothpaste tablets (fluoride-free, 5% nano-hydroxyapatite, chew then brush) are a favorite of mine, especially for travel. And get your nose working, so your saliva can do its job while you sleep.

Sugar still gets a vote

None of this lets sugar off the hook. Sugar is the most efficient fuel S. mutans has, and a diet high in it shifts the oral microbiome toward acid producers.

A child who drinks juice all day will get cavities no matter how well I explain the Stephan curve. Cutting sugar and cutting frequency are both levers, and most people have only heard about the first one.

Tape this to the pantry door

What causes cavities is acid at the tooth surface, made by bacteria fermenting whatever carbohydrate you feed them, on a clock that resets every time you eat or sip. Frequency drives the damage more than amount, saliva is the rescue, and mouth breathing or a dry mouth removes the rescue. Eat in fewer windows and keep sugar low; give your enamel hydroxyapatite and nasal breathing to rebuild between attacks.

Quick questions about cavities

Why do some people never get cavities? Mostly saliva and enamel. Some people make more saliva with more buffering power, breathe through their nose at night, and formed stronger enamel as children thanks to genes and good mineral and vitamin status. Their mouths recover between acid attacks, so mineral comes back before a hole can form.

Is fruit bad for your teeth? Fruit has fermentable sugar, so it drops plaque pH like any other carbohydrate. The bigger issue is timing. An apple with lunch is one acid dip; fruit nibbled across the afternoon keeps your enamel in the acid zone for hours. Eat it with meals, rinse with water after, and skip the sticky dried versions between meals.

What should I do right after eating to protect my teeth? Rinse with water or a pinch of baking soda. After eating, plaque pH stays below the danger line for roughly 20 to 40 minutes while saliva brings it back up, and a rinse helps that rebound. Chewing xylitol gum after a meal speeds it up too, and starves the cavity bacteria in the process.

Can you get cavities from sugar-free drinks? You can get acid erosion from them. Plain seltzer sits around a pH of 3 to 4, and kombucha can be lower, so sipping either all day bathes your enamel in acid without any bacteria needed. Drink them with meals or in one sitting, and follow with plain water.

Dr. Staci Whitman, DMD, FMCP, is a board-certified dentist and is certified in functional medicine. She is based in Portland, Oregon and is the author of SPIT (Crown, 2027).