What does sugar actually do to your teeth?

Sugar does not dissolve teeth directly. What it does is feed the bacteria living in dental plaque, and those bacteria produce acid — mainly lactic acid — which literally dissolves the mineral out of your enamel. Sugar is the fuel; the bacteria are the engine; the acid is what does the damage. How does tooth decay develop? follows that sequence step by step.

That distinction matters, because it explains why the answer to “how much sugar is too much?” is not a number of grams. It is a number of exposures.

Understanding decay first

To understand how sugar really affects your teeth, you have to understand how caries — decay, cavities — comes about.

Caries is a highly prevalent, chronic dental disease that causes destruction of the tooth surfaces. It is a multifactorial infection that occurs through demineralisation: the loss of mineral from enamel and dentine, the hard tissues of the tooth. That demineralisation is caused by organic acids produced by bacteria residing in dental plaque. The stages of dental decay sets out how far that can run before it is noticed, and if enamel is the hardest substance in the body, why do teeth break? explains why the hardest tissue you own is still vulnerable to a weak acid.

Numerous factors are involved:

Sugar is undoubtedly the most important dietary factor in this process. But it is one factor among several, which is why two people with identical diets can have very different decay rates.

One consequence people underestimate: because caries is a chronic disease rather than an accident, it does not stop on its own. It progresses at a rate set by those factors, and the only way to change the trajectory is to change the factors. How do I prevent dental decay? is the practical version of that argument.

How sugar is related to caries

Sugar — or any fermentable carbohydrate — is the most important food source for oral bacterial metabolism. That metabolism produces acid, primarily lactic acid, which dissolves tooth structure. The acid does something else too: it creates an acidic environment that further favours the growth and metabolism of exactly the bacteria that cause cavities. The process is self-reinforcing. A mouth that is frequently acidic selects for an increasingly acid-loving, acid-producing bacterial population.

By “fermentable carbohydrate” we mean any sugar or cooked starch that oral bacteria can digest into acid. That is not limited to sucrose — it includes fructose and glucose as well.

All fermentable carbohydrates contribute to some degree, but sucrose remains the biggest offender. It is uniquely damaging because it does two jobs at once: it lets bacteria produce acid, and it also lets them build the sticky extracellular polysaccharides that anchor even more bacteria to the tooth. Sucrose does not just feed the plaque; it helps build it.

Complex carbohydrates such as starch interact with bacteria to a lesser extent and are therefore less acid-producing. Cooked and refined starches — white bread, crackers, crisps — sit in between, particularly because they lodge in the grooves of the teeth and clear slowly. Those grooves are also why fissure sealants exist.

The four variables that decide the damage

The frequency, quantity, duration and physical form of dietary sugar all influence the caries process. In order of practical importance:

Variable Why it matters
Frequency Each exposure starts an acid attack lasting roughly 20–40 minutes before saliva restores a safe pH. Six exposures is six attacks; the mouth never fully recovers between them.
Duration / form Anything that keeps sugar in contact with the tooth extends the attack — sipped drinks, hard-boiled lollies, dried fruit, sticky muesli bars.
Timing Sugar at the end of a meal is far less damaging than the same sugar alone between meals, because saliva flow is already elevated. Sugar just before bed is the worst case: saliva flow drops to near zero overnight.
Quantity Real, but the weakest of the four. The same 30g of sugar does very different damage depending on the three above.

This is the single most useful thing to take away. A large dessert eaten in one sitting is less harmful than the same sugar sipped across an afternoon. A person who cuts total sugar but grazes on it all day may see their decay rate get worse, not better.

The same frequency logic is why sports drinks are linked to poor dental health in athletes — they are sipped slowly, during exercise, when saliva flow is already down. What are sports drinks really doing to your teeth? and how exercise can increase your risk of tooth decay cover the same trap from different angles.

Where the point of no return is

Early demineralisation is reversible. At the white-spot stage — a chalky, matte patch on the enamel, most often at the gumline or between the teeth — the mineral loss is sub-surface and can be re-mineralised with fluoride, better plaque control and reduced sugar frequency. This stage is painless and usually invisible to the person who has it. What causes white spots on teeth? covers the other things that produce the same appearance, and can you reverse tooth decay? is the fuller answer to where the line sits.

Once sugar has dissolved enough structure that a cavity has formed — the surface has collapsed — the damage is irreparable. It needs a restoration (a filling), or, if it has progressed further, more extensive treatment such as a crown or root canal treatment. Enamel has no living cells and does not regrow. From that point onwards the tooth is in a lifelong cycle of restoration and re-restoration, each one a little larger than the last — why do I need a filling? and porcelain, amalgam or composite resin? explain what that cycle involves and what it costs.

Pain, incidentally, is a late signal. By the time a cavity hurts, it has usually reached the dentine or the nerve. Absence of pain is not evidence of absence of decay — which is what check-ups and radiographs are for. Decay between the teeth is effectively invisible to the eye until it is large.

Hidden sugars

Many people are unaware of the numerous hidden sugars in everyday foods and drinks. The common surprises:

Check ingredient lists for the aliases: sucrose, glucose, fructose, maltose, dextrose, corn syrup, invert sugar, molasses, honey, fruit juice concentrate, agave. All are fermentable.

One clarification worth making: sugar-free does not mean tooth-safe. Sugar-free soft drinks and sparkling waters contain acids — citric, phosphoric, carbonic — that erode enamel directly, without any bacterial involvement. They cause less decay, but they can still cause erosion. Are sugar-free soft drinks better for my teeth? is the long answer; is soda water bad for your teeth?, what impact does wine have on my teeth? and how does acidic food affect your teeth? extend it to the rest of the drinks trolley. What is acid wear and how can I avoid it? and what is dental erosion and how is it addressed? describe the damage itself.

What to do about it

Diet assessment and modification are a routine part of a comprehensive dental examination. Being honest about what you actually consume, and how often, is more useful to your dentist than the total on a nutrition label — because the pattern, not the number, is what decides whether you get cavities.

So next time you reach for something sweet, think not only of your waistline but also your smile line.

Common questions

Fine — but how much sugar am I actually allowed in a day?

There is a published number, and it is smaller than most people expect. The World Health Organization recommends reducing free sugars to less than 10 per cent of total energy intake, and suggests going further, to below 5 per cent, to reduce the risk of tooth decay. The Australian Dental Association translates that into a figure you can use in a supermarket: oral health education should encourage limiting consumption to "no more than 6 teaspoons (24 grams of free sugar (5% of total energy intake) per day".

For scale, the ADA's consumer site puts one can of soft drink at an average of 10 teaspoons of sugar — about 1.5 times the entire daily recommendation. One can. Before anything you ate.

Two things stop that number being the whole answer, and they are both on this page already. First, the ADA's own policy states that "the form, frequency, timing and total amount of sugar intake are significant in the initiation of the caries process" — quantity is one of four variables, and the weakest of them for decay. Second, the number counts free sugars, which the WHO defines as all sugars added by the manufacturer, cook or consumer plus those naturally present in honey, syrups, fruit juices and fruit juice concentrates.

So use the six teaspoons as a budget and the frequency rule as the spending plan. Spending it in one sitting after a meal is a very different proposition from spending it in eight sips across a working day, even though the label total is identical.

How do I find the sugar on a label when it is not called sugar?

Two habits do almost all of the work here, and both come from the ADA's consumer guidance.

Use the per-100-gram column, not the per-serve column. Serving sizes are set by the manufacturer and differ between products, so per-serve figures compare, in the ADA's phrase, "apples with oranges". Against the 100 g column its thresholds are: 5 grams of sugar or less is best, between 5 g and 10 g is okay, and over 15 g means looking for a healthier alternative.

Then read the ingredients, because sugar travels under aliases. The ADA notes that sugars can be called over 50 different names, and lists examples including sucrose, maltose, lactose, fructose, brown rice syrup, glucose syrup, palm sugar, agave nectar, golden syrup, honey, molasses, corn syrup, cane sugar, maltodextrin and raw sugar. Its other rule of thumb: the closer an ingredient sits to the top of the list, the more of it is present.

One limitation to know about. Many products do not state how much of the sugar is added rather than naturally present, which is why the ingredient list often tells you more than the nutrition panel. The ADA's own policy position is that declaring both "total sugars" and "added sugars" should be mandatory — which is a fair indication that the labelling is not yet doing the job for you.

Is natural sugar — fruit, honey, juice — better for my teeth than added sugar?

For your teeth specifically, the ADA's consumer answer to that exact question is one word: yes, they affect teeth the same way. Plaque bacteria ferment the sugar; they do not check its provenance.

But the ADA immediately qualifies it, and the qualification is the useful part. Whole foods such as fruit and milk contain small amounts of natural sugars alongside fibre, vitamins and minerals which are good for the body, and milk also contains calcium, which can help to protect your teeth and bones. Processed foods with large amounts of added sugar frequently have no or limited nutritional value. So a piece of fruit and a lolly are not equivalent as food, even though the bacteria treat their sugar identically.

Three specific cases where "natural" misleads people:

Practical resolution: treat fruit as food and juice as a sweet drink, and judge both by the frequency rule rather than by the word on the packaging.

How do I handle sugar with children without banning everything?

Target the pattern rather than the item, because that is where the evidence points. The ADA's dietary education position names the high-risk groups explicitly, and the advice for each is about habits rather than prohibition.

What that looks like in a household, without a daily argument:

And keep the tone off the food. A child who is told sweets are forbidden learns to eat them quickly and secretly, which is the worst version of every variable in the table above. See protecting your child from dental disease and Dental Health Week: protect your kids from the Sugar Bandits.

Related reading

Practical details

Figures and positions attributed to the World Health Organization and the Australian Dental Association are those organisations’ own, as at the dates of the documents cited.

Specialist registration can be verified on the AHPRA register, or by calling 1300 419 495. The clinical team is listed by name.

Smile Solutions, Level 1, 220 Collins Street, Manchester Unity Building, Melbourne VIC 3000 — getting here. Phone 13 13 96, contact us, or theteam@smilesolutions.com.au. Monday–Friday 8.00am–6.00pm, Saturday 8.30am–1.30pm, Sunday by appointment. Fee ranges for examinations, cleans and fillings are set out in the price guide.

Published 25 September 2014. General information only; it does not replace advice from your treating practitioner.

Smile Solutions trades under ABN 28 193 514 103.

Images on This Page