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Tooth Decay: Causes, Signs, Treatment and Prevention

Tooth decay starts when plaque bacteria turn sugar into acid that weakens your teeth. Found early it can be stopped, and most decay can be prevented with simple daily habits.

Updated September 2026·By the OHA editorial team·6 min read·How we write
Key takeaways
  • Tooth decay happens when bacteria in plaque turn sugar from food and drink into acid, which dissolves minerals from the surface of your teeth.
  • Early decay usually has no symptoms. A white spot can be the first sign, and at that stage the damage can often be stopped or reversed.
  • Once a hole (cavity) forms you will usually need a filling. Deeper decay may need root canal treatment, and sometimes the tooth has to be removed.
  • Brush twice a day with fluoride toothpaste, clean between your teeth every day, cut down on sugary food and drinks, and have regular check-ups.
  • A swollen face or jaw, a high temperature, or trouble breathing or swallowing with a bad tooth needs urgent help.

Tooth decay is very common. The Australian Dental Association calls it the most common chronic (long-lasting) disease in Australia, and healthdirect Australia reports that about 1 in 3 Australian adults aged over 15 has tooth decay that has not been treated. It can affect anyone who has teeth, from young children to older adults. The encouraging part is that the Australian Dental Association describes it as almost entirely preventable, and early decay can often be stopped before it turns into a hole.

How does tooth decay happen?

Decay starts with plaque, a sticky film of bacteria that forms on your teeth all the time. When you eat or drink something containing sugar, the bacteria use it to make acid. The US National Institute of Dental and Craniofacial Research (NIDCR) says starchy foods feed this process too.

The acid attacks enamel, the hard outer layer of the tooth, and dissolves some of its minerals. The Australian Dental Association calls this demineralisation. Saliva and fluoride fight back by helping to stop the acid and putting minerals back into the enamel (remineralisation). The Australian Dental Association describes decay as a balancing act: it develops when the harmful factors outweigh the protective ones.

According to NIDCR, a white spot may appear where minerals have been lost, and this is a sign of early decay. If more minerals keep being lost than can be restored, the enamel breaks down and forms a cavity (a hole in the tooth).

What makes decay more likely?

healthdirect says you are more likely to get tooth decay if you eat a lot of sugary foods, snack often, do not clean your teeth regularly, have a dry mouth, smoke, or do not have regular dental check-ups.

How often you have sugar matters. The Australian Dental Association explains that frequent snacking or sipping on sugary drinks does the most damage, because your teeth do not get time to recover before the next acid attack. It also warns about sugars hidden in foods such as breakfast cereal, bread and ready-made sauces, and lists soft drinks, energy drinks, cordial and fruit juice as drinks that can cause decay.

Age plays a part too. healthdirect says children's teeth have softer, thinner enamel and decay more easily. In older adults, gums often shrink back and expose the tooth roots, which the American Dental Association says are covered by a softer tissue than enamel and more likely to decay.

What are the signs of tooth decay?

Early decay usually causes no symptoms at all. The NHS, NIDCR and healthdirect all make this point, which is why regular check-ups matter. healthdirect notes that an early white spot is often visible near the gumline, but not if it is in the grooves of your back teeth.

As decay gets worse, the NHS and healthdirect say you may notice:

  • toothache
  • a sharp pain when you eat or drink something hot, cold or sweet (sensitive teeth)
  • white, brown or black spots or stains on a tooth
  • pain when you bite or chew
  • red and swollen gums near the decayed tooth

If decay is left untreated, healthdirect lists possible complications including pain, damaged or broken teeth and problems chewing. The tooth can also become infected: NIDCR explains that an abscess (a pocket of pus) may form, causing pain, facial swelling and fever. The NHS says a dental abscess needs urgent treatment by a dentist and will not go away on its own.

A dentist checks for decay by examining your teeth and asking about symptoms. NIDCR says they may check for soft or sticky areas and take an x-ray, which can show decay you cannot see.

How is tooth decay treated?

Treatment depends on how far the decay has gone.

Early decay: fluoride

If decay is caught before a hole forms, it can often be stopped. The NHS says a dentist can prescribe fluoride treatments, such as a mouthwash or varnish (a fluoride coating painted onto the teeth), to reverse early decay. healthdirect adds that brushing with fluoride toothpaste and improving your diet at home are part of this. The Australian Dental Association notes that a white or brown mark may remain on the tooth, rather like a scar.

A filling

If there is a hole in the tooth, the NHS says you will probably need a filling. The dentist removes the decayed part of the tooth and fills the space.

Root canal treatment

If decay reaches the pulp (the soft tissue in the middle of the tooth), the NHS says you may need root canal treatment. Under local anaesthetic, so you are awake but do not feel pain, the dentist removes the infected pulp, cleans the inside of the tooth, then fills and seals it. The NHS says this usually takes 2 or more appointments, and a crown (a cap that completely covers the tooth) may be needed if the tooth was badly infected.

Removing the tooth

The NHS says that sometimes the affected tooth may need to be taken out (an extraction). healthdirect points out that after a tooth is lost, the other teeth may move into the gap, so it is worth talking to your dentist about your options.

How can you prevent tooth decay?

The Australian Dental Association recommends four steps:

  1. Brush your teeth twice a day with a fluoride toothpaste.
  2. Clean between your teeth every day, with floss or interdental brushes.
  3. Eat a healthy diet that is low in sugar.
  4. Visit the dentist regularly.

A few details make these steps work better:

  • Spit, don't rinse. After brushing, spit out the toothpaste but do not rinse with water, so the fluoride keeps working. The NHS, healthdirect and the Australian Dental Association all give this advice.
  • Keep sugar to mealtimes. healthdirect suggests that if you have sugary food and drinks, it is best to have them with meals.
  • Drink tap water. healthdirect says most Australian tap water has fluoride added, and NIDCR lists fluoridated tap water as one way to get fluoride.
  • Choose sugar-free medicines where you can, and do not smoke, as the NHS advises.

Your dentist may also suggest sealants, a protective coating on the grooves of the back teeth, where decay often starts and cleaning is harder. healthdirect, NIDCR and the American Dental Association all mention them.

How often should you have a check-up?

Advice differs by country. The NHS says your dentist will advise how often you need a check-up, and that you should see a dentist if you have not had one for 2 years (1 year if you are under 18). healthdirect Australia says many dental health experts recommend a check-up every 6 months.

When to see a dentist
  • You have toothache, or a sharp pain when eating or drinking something hot, cold or sweet.
  • You notice a white, brown or black spot, or a hole, on a tooth.
  • It hurts when you bite or chew.
  • The gum near a tooth is red, swollen or painful.
  • You have not had a dental check-up for 2 years or more.
Get help urgently
  • Ask for an urgent dental appointment if you think you have a dental abscess: intense toothache, a swollen face or jaw, a bad taste in your mouth or a high temperature. In the UK, the NHS says to call your dentist or NHS 111, and not to go to a GP surgery, as they cannot give dental treatment. In Australia, the healthdirect helpline (1800 022 222) can advise 24 hours a day.
  • Call emergency services or go to an emergency department if you are finding it hard to breathe, speak or swallow, have a swollen or painful eye or sudden problems with your eyesight, have a lot of swelling in your mouth, or are finding it hard to open your mouth.

Frequently asked questions

Can early tooth decay heal?

It can be stopped, and sometimes reversed, if it is caught early. NIDCR explains that at the white-spot stage, enamel can repair itself using minerals from saliva and fluoride from toothpaste or from a dentist. Once a hole has formed, you will usually need a filling.

Is fruit bad for my teeth?

Fruit contains natural sugar, but the Australian Dental Association says fresh fruit is less likely to contribute to decay than sugar added to foods and drinks. It describes fresh fruit as a more tooth-friendly choice than dried fruit or fruit juice, and milk and cheese as tooth-friendly options.

Why do I keep getting decay around my old fillings?

The American Dental Association explains that fillings can weaken over the years and may crack or leak around the edges. Bacteria collect in these tiny gaps and produce acid, which leads to decay. It says this is common in older adults.

Sources

  1. Tooth decay, NHS, accessed September 2026
  2. Dental abscess, NHS, accessed September 2026
  3. Root canal treatment, NHS, accessed September 2026
  4. Tooth decay, healthdirect Australia, accessed September 2026
  5. Tooth decay, Australian Dental Association, accessed September 2026
  6. Tooth decay, National Institute of Dental and Craniofacial Research (NIH), accessed September 2026
  7. Tooth decay, American Dental Association (MouthHealthy), accessed September 2026

This article is general information about oral health. It is not a diagnosis or a substitute for advice from a dentist or doctor who knows your situation. If you have pain, swelling, bleeding that does not settle, or a problem that is getting worse, see a dental professional. In an emergency, contact your local emergency service.

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