Cavities and Tooth Decay: What They Are, Why They Happen, and How to Protect Your Teeth

Short answer

• A cavity is the hole; tooth decay is the process. Dental caries is the clinical name for tooth decay. Bacteria in plaque make acids from sugars and starches, the acids draw minerals from enamel, and when enamel breaks down, a cavity is left.
• Early decay can sometimes be stopped or reversed. Before a hole forms, enamel can repair itself using minerals from saliva and fluoride. A white spot where minerals have been lost can be a sign of this early stage.
• A formed cavity cannot heal on its own. Enamel that has broken down does not regrow, and brushing cannot close a hole. A dentist repairs that damage, commonly with a filling.
• Frequency matters as much as quantity. Every sugary or starchy exposure starts another acid attack. Frequent snacking and sipping sweet drinks give enamel little time to recover.
• Early decay usually causes no symptoms. Pain is a late and unreliable warning. As decay advances it can cause toothache, sensitivity to sweets, hot, or cold, staining, a visible hole, and, if the tooth becomes infected, swelling and fever.
• Treatment follows the stage. Fluoride for early decay, a filling for a formed cavity, a crown where a tooth is badly weakened, root canal treatment where decay has reached the pulp, and removal only where a tooth cannot be restored.
• Prevention is a daily pattern. Brush twice a day with fluoride toothpaste, clean between teeth daily, limit sugary food and drink and snacking, ask about sealants and extra fluoride, and keep regular check-ups.
• This guide is general information only, not a diagnosis. Swelling, fever, severe pain, or trouble breathing, speaking, or swallowing needs prompt or emergency care, not home monitoring.

Introduction

A cavity is a hole in a tooth, and tooth decay is the process that makes it. Bacteria that live in the mouth feed on sugars and starches and produce acids. Those acids draw minerals out of enamel, the hard outer layer of the tooth. For a while the process can move in both directions, because saliva and fluoride can put minerals back. When mineral loss keeps winning, enamel breaks down and a hole forms. Once that has happened, the missing structure does not grow back on its own.

This article explains that process in plain language: what decay is, how demineralization works, what raises the risk, what symptoms can appear at each stage, how treatment is chosen in outline, and which daily habits protect teeth best. It also explains the one distinction that matters most: early decay, before a hole forms, can sometimes be stopped or reversed, while an established cavity needs professional treatment.

This article is general information only. It does not diagnose any tooth and it is not a treatment plan for any individual. If you think you may have a cavity, the safest step is a dental examination, rather than waiting for pain or trying to remove decay yourself.

What a Cavity Is, and What Tooth Decay Is

Keeping the two terms apart makes everything else clearer. Tooth decay, called dental caries, is the damage. A cavity is one result of that damage: a hole in the tooth. The National Institute of Dental and Craniofacial Research (NIDCR) puts it in one line: tooth decay begins when bacteria in the mouth make acids that attack the tooth surface, and that can lead to a small hole in a tooth, called a cavity.

MouthHealthy, the American Dental Association patient site, describes decay as the destruction of enamel, the hard outer layer of the teeth. Plaque, a sticky film of bacteria, constantly forms on teeth. When you eat or drink foods containing sugars, the bacteria in plaque produce acids that attack enamel, and plaque’s stickiness keeps those acids in contact with the tooth. Over time, enamel can break down, and that is when cavities form.

Decay can affect baby teeth and adult teeth, at any age once teeth are present. A cavity can sit on a chewing surface, a smooth side surface, between two teeth, or at the gum line. Size alone does not settle how serious it is: a small hole between teeth can be well advanced underneath, while a white spot that has not broken the surface may need only fluoride and monitoring.

How Decay Forms: The Demineralization Process

The NIDCR describes the mouth as a tug of war that runs all day. On one side are dental plaque and foods and drinks containing sugar or starch, such as milk, bread, cookies, candy, soda, and juice. Whenever something containing sugar or starch is eaten or drunk, bacteria use it to produce acids, and those acids begin to eat away at enamel. On the other side are the minerals in saliva, such as calcium and phosphate, plus fluoride from toothpaste, water, and other sources. That side helps enamel repair itself by replacing the minerals lost during an acid attack.

Demineralization is the loss side of that contest: acid draws minerals out of enamel. Remineralization is the repair side: saliva and fluoride put minerals back. Teeth go through this cycle of losing and regaining minerals all day long, which is why pattern matters more than any single meal.

The sequence runs like this. A tooth is exposed to acid frequently, through repeated sugary or starchy food and drink. Enamel keeps losing minerals. A white spot may appear where minerals have been lost, a sign of early decay. At that point decay can be stopped or reversed, because enamel can repair itself using minerals from saliva and fluoride. If more minerals are lost than can be restored, enamel weakens and is eventually destroyed, forming a cavity. The NIDCR calls a cavity permanent damage that a dentist has to repair with a filling.

There is no single timeline for how long a cavity takes to form. The rate depends on how often acid attacks happen, how well saliva and fluoride repair works, and where decay starts. Decay in a deep groove or between teeth can progress for a long time with no symptoms, so a dentist monitoring a weak spot over visits can say more than any guess from symptoms alone.

Where Cavities Form

Decay starts where plaque sits undisturbed longest. Between teeth is a common site, because plaque and food collect at the contact point where a toothbrush cannot clean well. The chewing surfaces of back teeth are another: the NIDCR explains that those surfaces are rough and uneven, with small pits and grooves where food and bacteria can get stuck for a long time because toothbrush bristles cannot easily clean them away.

Front teeth are often noticed sooner because they are visible, but visibility says nothing about depth. Surfaces near the gum line carry a different risk. MouthHealthy explains that gum recession can expose tooth roots to plaque, that roots are covered with cementum, a softer tissue than enamel, and that they are susceptible to decay. Root decay is common for people over age 50. The NIDCR makes the same point for older adults: receding gums let decay causing bacteria reach the root, so decay can form on exposed root surfaces.

Decay can also form at the edge of an existing filling, because, as MouthHealthy notes, fillings can weaken over the years and leak around the edges, letting bacteria accumulate in tiny crevices. And young children are at risk of early childhood caries, which the NIDCR says can start in a baby’s front teeth and extend to the back teeth. What decay looks like at each of these sites is covered in our article on what a cavity looks like.

Stages of Decay, and What Each Stage Can Feel Like

Stages describe a progression, not a set of fixed dates, and a tooth does not announce which stage it has reached. The table below follows the sequence set out by the NIDCR and the NHS.

Stage	What is happening in the tooth	What you may notice	General direction of care
Early mineral loss	Acids draw minerals from enamel; the surface is still closed	Often nothing; a white spot may appear	Fluoride, better cleaning, fewer sugary exposures, and monitoring
Enamel breakdown	Enamel weakens and breaks down; a small hole forms	A pit, rough area, or staining; often still no pain	A filling is usually needed once a hole has formed
Dentin involvement	Decay reaches dentin, the softer layer under enamel, and can spread faster there	Sensitivity to sweet, hot, or cold foods and drinks becomes more likely	A filling, or a crown where the tooth is weakened
Pulp involvement	Decay reaches the pulp, the inner tissue with nerves and blood vessels	Toothache becomes more likely; infection can follow	Root canal treatment may be needed to save the tooth
Abscess	Infection forms a pocket of pus in or around the tooth	Pain, facial swelling, and fever can occur	Prompt professional care; a tooth that cannot be restored may need removal

Two cautions belong with that table. Dentin is softer than enamel, so decay speeds up once it reaches dentin. And color does not stage a tooth: a brown spot can reflect more advanced mineral loss or simple staining, and only an examination can tell which.

What Causes Cavities, and What Raises the Risk

The direct cause is acid from bacteria acting on sugars and starches. The World Health Organization states the chain plainly: dental caries results when plaque forms on the surface of a tooth and converts the free sugars in foods and drinks into acids that destroy the tooth over time, and a continued high intake of free sugars, inadequate exposure to fluoride, and a lack of removal of plaque by toothbrushing can lead to caries, pain, and sometimes tooth loss and infection. Around that direct cause, several factors decide how often the acid side wins.

• Frequent sugar and starch intake. It is not only how much sugar is eaten, but how often. Sipping a sweet drink over hours or snacking often gives bacteria repeated chances to make acid. Our explainer on sugar and teeth covers why frequency matters most.
• Plaque that stays on the teeth. Plaque that is not removed can harden into tartar. Brushing and cleaning between teeth remove plaque; tartar is a different problem, covered in our guide to how to remove plaque from teeth.
• Low fluoride exposure. Fluoride prevents mineral loss in enamel, replaces lost minerals, and reduces the ability of bacteria to make acid, in the NIDCR’s summary. Low exposure removes that protection.
• Dry mouth. MouthHealthy calls saliva the mouth’s primary defense against tooth decay: it washes away food and debris and neutralizes acids produced by bacteria. Dry mouth results from an inadequate flow of saliva and can be a side effect of certain medications or a symptom of a medical disorder. Without saliva, extensive tooth decay can occur.
• Tooth shape and position. Deep grooves on back teeth, crowded teeth, and surfaces that are hard to clean trap plaque and food where a brush cannot reach.
• Earlier decay and existing dental work. A tooth that has decayed before, and margins around older fillings, are places where bacteria can accumulate again.

None of this makes decay inevitable. It means the balance of acid attack and repair needs more support, and a dentist can help identify where that support will do most good.

Symptoms by Stage

Cavity symptoms are often absent in early decay. The NIDCR states it directly: in early tooth decay, there are not usually any symptoms. A tooth can be decaying without hurting, so pain is not a reliable early warning and waiting for pain is a poor strategy.

As decay advances, the NIDCR lists toothache and tooth sensitivity to sweets, hot, or cold. The NHS adds the visible side: if a hole has formed, you may have toothache, sharp pain when eating or drinking hot, cold, or sweet things, and white, brown, or black spots on the tooth. NHS inform adds bad breath and an unpleasant taste in the mouth to the list of possible signs.

Signs worth reporting at an examination include:

• Sensitivity that lingers after hot, cold, or sweet food or drink
• Sharp pain when biting, or when food presses into one tooth
• A toothache that comes and goes, or that becomes steady
• Brown, black, or white staining on a tooth surface
• A visible hole, pit, or rough area, or food packing into the same place repeatedly
• A persistent bad taste, or bad breath linked to one damaged tooth

How a cavity tends to feel is covered in our article on what a cavity feels like, and whether decay can explain bad breath in our article on whether cavities cause bad breath. One direct answer on pain: a cavity can be painful, especially once decay reaches dentin or pulp, but cavities do not hurt in every case, and pain can also come from gum problems or a cracked tooth. Pain alone cannot name the cause.

How You Can Tell, and How a Dentist Tells

You can watch for the signs above. You cannot confirm a cavity by looking in a mirror alone, because early decay and decay between teeth may be invisible, and a dark spot is not always decay.

A dentist works differently. The NIDCR explains that decay can be found during a regular check-up: signs include white, brown, or black staining, a hole if decay is more advanced, and the dentist can also check for soft or sticky areas or take an X-ray, which can show decay. That examination, not a photograph or a mirror check, is how a cavity is diagnosed. If swelling, fever, severe pain, or a broken tooth is present, seek prompt care rather than a routine appointment.

Can a Cavity Go Away on Its Own

The answer depends on the stage, and blurring the two cases causes real harm. Early decay, before a hole forms, can be stopped or reversed. The NIDCR states that enamel can repair itself using minerals from saliva and fluoride from toothpaste, or through fluoride applied by a dentist or dental hygienist. That is why a dentist may recommend fluoride, better cleaning, fewer sugary exposures, and monitoring for a white spot whose surface has not broken down.

Once a hole has formed, a cavity cannot go away on its own. The tooth cannot regrow broken down enamel, and brushing cannot close the hole. Treatment is then needed to remove decayed tissue and restore the tooth, and waiting usually lets decay spread deeper. What can and cannot be done at home, and what a dentist does instead, is covered in full in our article on how to get rid of cavities and what treatment involves. Newer approaches that aim to stop early decay without drilling are examined, with their limits, in our article on stopping cavities without drilling. Trying to scrape, pick, or drill at a tooth yourself is not safe: it can damage enamel, injure gums, and miss decay hidden between teeth or under a surface.

Treatment in Outline

Treatment is chosen by how far decay has reached, and the right option for a particular tooth depends on the tooth, the depth of decay, symptoms, and the examining dentist’s findings. This section is an overview only.

Fluoride for early decay. If decay is still in its early stages, before a hole forms, the NIDCR states that a dentist can apply fluoride to reverse the decay. The NHS describes the same step as fluoride treatments, such as mouthwash or varnish, prescribed to reverse early decay, alongside advice about sugar in the diet.

A filling for a formed cavity. Dentists commonly treat cavities by filling them: the dentist removes the decayed tooth tissue and restores the tooth by filling it with a filling material. How long such a repair lasts, and the signs that one needs replacing, are covered in our guide to how long a cavity filling lasts.

A crown where a tooth is badly weakened. Where a filling alone cannot support what remains, a crown, a cover that protects the tooth, may be recommended. NHS inform describes dentists discussing a filling or a crown for more advanced decay, and MedlinePlus notes that after root canal treatment a tooth may need a permanent filling or a crown.

Root canal treatment where decay reaches the pulp. The NHS states that if decay has reached the soft tissue, the pulp, in the middle of the tooth, root canal treatment may be needed. MedlinePlus describes it in general terms: the decayed pulp is removed, the inside of the tooth and root is cleaned, and the tooth is then filled and later restored. How decay reaches that stage is explained in how cavities turn into root canals.

Extraction where a tooth cannot be restored. Sometimes the affected tooth may need to be removed, in the NHS’s wording. MedlinePlus describes extraction as the option for the most severe cases, when damage cannot be fixed, and notes that a dentist may suggest a bridge or implant to replace the tooth, because neighboring teeth can otherwise move and change the bite. Removal is a last resort, not a first response.

How to Protect Your Teeth: Prevention That Works

Prevention is where daily habits have the most power, and the advice is consistent across the NIDCR, MouthHealthy, the NHS, and the WHO. The WHO adds one framing point: adequate exposure to fluoride is an essential factor in prevention, and twice daily brushing with fluoride toothpaste should be encouraged.

• Brush twice a day with fluoride toothpaste. Clean all surfaces, including along the gum line. The NHS advises: brush at least twice a day with fluoride toothpaste, and spit after brushing rather than rinsing, so fluoride stays on the teeth longer.
• Clean between teeth daily. Use floss or another interdental cleaner. This matters most for cavities between teeth, where a brush cannot reach. MouthHealthy and the NIDCR give the same advice.
• Use fluoride in its everyday forms. Fluoride toothpaste is the baseline. The NIDCR also lists drinking tap water that has fluoride and using fluoride mouth rinse, and a dentist may recommend supplemental fluoride where risk is higher. Ask about toothpaste strength if you are unsure, especially for young children.
• Limit sugary food and drink, and limit snacking. The NIDCR advises smart food choices that limit sugary drinks and foods high in sugars and starches, balanced meals, and limited snacking, because limiting between meal snacks reduces the number of acid attacks and gives teeth a chance to repair themselves. Water is a better everyday drink than sweet drinks.
• Ask about sealants. Sealants are thin coatings painted onto the chewing surfaces of the back teeth, covering the pits and grooves where food and bacteria get stuck. The NIDCR advises talking to a dentist about sealants when a child’s permanent teeth come in, and MouthHealthy advises asking about sealants for the back teeth, where decay often starts.
• Keep regular check-ups and professional cleanings. A check-up can find early decay before it hurts, and a dentist can give personal advice on fluoride, sealants, and cleaning technique.
• Do not use tobacco products, including smokeless tobacco. The NIDCR lists this among its prevention tips, and the WHO lists stopping all forms of tobacco among its prevention measures.
• Raise dry mouth with a dentist. Saliva is part of the repair system, so persistent dryness is worth discussing rather than enduring. Drink water through the day, and mention any medicines you take, because dry mouth can be a medication side effect.

For children, the same principles apply with age-appropriate amounts of fluoride toothpaste and supervision, and with attention to bottles and frequent sweet drinks, including juice. For older adults, attention shifts to receding gums and exposed roots, dry mouth, and cleaning around crowns, bridges, and older fillings.

No specific toothpaste brand is recommended here, deliberately. A dentist or pharmacist can advise on a suitable fluoride toothpaste for your age and risk level.

What to Do While You Wait for an Appointment

Keep the tooth as clean as you can with gentle brushing and cleaning between teeth, unless that causes severe pain, in which case stop and seek advice sooner. Avoid very hot, very cold, and very sweet foods and drinks if they trigger sensitivity. Do not try to scrape, pick, or fill a hole yourself, and do not rely on a home remedy that claims to remove an established cavity.

If pain is present, contact a dental practice promptly and describe the pain, when it started, what triggers it, and whether swelling or fever is present. That helps the practice judge urgency. Keep a short note of what you have tried and what helped.

When to Seek Care Promptly

Most cavities are not emergencies, but some situations need prompt care. The NIDCR notes that if a tooth becomes infected, an abscess, a pocket of pus, may form, causing pain, facial swelling, and fever. The CDC warns that untreated cavities can lead to an abscess, a severe infection that can spread to other parts of the body and have serious, and in rare cases fatal, results.

Seek prompt professional care if you have swelling in the face or around a tooth, fever with tooth pain, severe pain that does not settle, a broken tooth, pus or a bad taste linked to a tooth, or difficulty opening your mouth or chewing. The NHS lists those abscess signs, including intense toothache, redness, a bad taste, a swollen face or jaw, swollen glands, and a high temperature, and advises asking for an urgent dentist appointment if you think you have a dental abscess.

Trouble breathing, speaking, or swallowing, a lot of swelling in your mouth, a swollen or painful eye or sudden vision problems, or finding it hard to open your mouth require immediate emergency medical attention, not a routine dental wait. The NHS gives that same immediate action advice for a dental abscess. Use the emergency service for where you are.

Frequently Asked Questions

What are dental caries? Dental caries is the clinical name for tooth decay, the process in which bacteria in plaque make acids that draw minerals from enamel and, if unchecked, create a cavity. Tooth decay names the process, and cavity names the hole that results.

Can cavities go away without treatment? Early decay can, and a formed cavity cannot. Before a hole forms, fluoride and better daily care can stop or reverse mineral loss, under a dentist’s guidance. Once enamel has broken down, the missing structure does not regrow, and professional treatment is needed.

How do I know if I have a cavity? You often cannot know on your own. Watch for sensitivity, pain, staining, a hole, or pain when biting, but remember that early decay usually has no symptoms. The reliable way to know is a dental examination, which may include an X-ray to show decay hidden between teeth or under a filling.

Does a cavity always hurt? No. Early cavities often do not hurt, and even larger ones can be painless for a time. Pain becomes more likely as decay reaches dentin and the pulp. Pain that is severe, wakes you at night, or comes with swelling or fever needs prompt care.

Can a small cavity stay small? It can stay stable for a time, but that cannot be assumed. Dentin breaks down faster than enamel, and decay between teeth or under a surface can spread without symptoms. A dentist who monitors the tooth can judge whether it is stable or needs a filling.

How long does it take for a cavity to form? There is no single timeline. It depends on how often acid attacks happen, how strong saliva and fluoride repair is, and where decay starts. Frequent sugary exposures speed the process; spacing food and drink and using fluoride slow it.

Can tooth decay affect teeth that already have fillings? Yes. Decay can form at the edge of a filling, between teeth, or on an exposed root, and a filled tooth is not immune to new decay. Regular check-ups, cleaning between teeth, and fluoride help protect filled teeth as well as natural surfaces.

What is the single most useful step to prevent cavities? If one habit has to come first, make twice daily brushing with fluoride toothpaste steady, because fluoride works on every surface at every age. Then add daily cleaning between teeth, then look at sugary drink and snacking frequency.

Sources & references

• National Institute of Dental and Craniofacial Research, Tooth Decay. Explains that bacteria make acids that attack enamel and can lead to a cavity, that repeated acid exposure causes mineral loss and a white spot as a sign of early decay, that early decay can be stopped or reversed with minerals from saliva and fluoride, that early decay usually has no symptoms, that advancing decay can cause toothache, sensitivity, and an abscess with pain, facial swelling, and fever, that diagnosis at a check-up includes staining, a hole, soft or sticky areas, and an X-ray, and that treatment includes fluoride before a hole forms and fillings. It also lists prevention tips and early childhood and root decay notes. Opened and read first hand on 3 November 2026.
• National Institute of Dental and Craniofacial Research, The Tooth Decay Process: How to Reverse It and Avoid a Cavity. Explains the daily tug of war between plaque, sugars and starches, saliva minerals, and fluoride, fluoride preventing mineral loss, replacing lost minerals, and reducing bacteria's ability to make acid, frequent eating raising acid attacks, limiting between meal snacks, sealants covering the pitted, grooved chewing surfaces of molars, and regular check-ups. Opened and read first hand on 3 November 2026.
• American Dental Association, MouthHealthy, Tooth Decay. Describes decay as destruction of enamel, plaque as a sticky film of bacteria producing acids when sugars are eaten or drunk, gum recession exposing roots covered with softer cementum that are susceptible to decay, root decay as common over age 50, and decay around filling margins as fillings weaken and leak. Prevention tips include brushing twice a day with fluoride toothpaste, cleaning between teeth daily, limiting snacking, supplemental fluoride and sealants, and regular dental visits. Opened and read first hand on 3 November 2026.
• American Dental Association, MouthHealthy, Dry Mouth. States that dry mouth results from an inadequate flow of saliva, that it can be a side effect of certain medications or a symptom of a medical disorder, that saliva is the mouth's primary defense against tooth decay because it washes away food and debris and neutralizes acids, and that without saliva, extensive tooth decay can occur. Opened and read first hand on 3 November 2026.
• NHS, Tooth Decay. Page last reviewed 13 August 2025. States that decay may not cause symptoms at first, that a hole may come with toothache, sharp pain with hot, cold, or sweet things, and white, brown, or black spots, that the tooth or gum can become infected leading to a dental abscess, and to get regular check-ups even without problems. Treatment depends on severity: fluoride can reverse early decay, a filling is likely for a hole, decay reaching the pulp may need root canal treatment, and a tooth may sometimes need removal. Prevention includes brushing twice a day with fluoride toothpaste, spitting and not rinsing, and cleaning between teeth every day. Opened and read first hand on 3 November 2026.
• NHS, Dental Abscess. Page last reviewed 18 March 2026. Lists abscess symptoms including intense toothache, redness, a bad taste, difficulty opening the mouth and chewing, a swollen face or jaw, swollen glands, and a high temperature, advises an urgent dentist appointment if you think you have an abscess, and gives immediate action for hard breathing, speaking, or swallowing, a lot of mouth swelling, a swollen or painful eye or sudden vision problems, and difficulty opening the mouth. Opened and read first hand on 3 November 2026.
• NHS inform, Tooth Decay. States that acid produced by plaque causes holes or cavities, lists symptoms including continuous or sharp toothache, sensitivity, grey, brown, or black spots, bad breath, and an unpleasant taste, and describes treatment by stage: fluoride gel, varnish, or paste for early decay, a filling or crown for more advanced decay, root canal treatment where decay has spread to the pulp, and removal where a tooth cannot be restored. It also explains that dentine is softer than enamel so decay speeds up there, and that bacteria entering the pulp can cause an abscess. Opened and read first hand on 3 November 2026.
• MedlinePlus, Tooth Decay (National Library of Medicine; NIH: National Institute of Dental and Craniofacial Research). Summarizes causes including plaque hardening into tartar, risk factors including not enough saliva because of medicines, certain diseases, or some cancer treatments, not enough fluoride, very young children given bottles or juice, and older adults with receding gums, and treatments: fluoride for early decay, fillings, root canal with a later permanent filling or crown, and extraction in the most severe cases with a possible bridge or implant. Opened and read first hand on 3 November 2026.
• Centers for Disease Control and Prevention, Cavity Facts, Oral Health. Fast facts dated 15 May 2024. States that cavities, also called tooth decay, often go untreated, that untreated cavities can cause pain and infections, and that untreated cavities can lead to an abscess, a severe infection that can spread to other parts of the body and have serious, and in rare cases fatal, results. Opened and read first hand on 3 November 2026.
• World Health Organization, Oral Health fact sheet. Published 17 March 2025. States that dental caries results when plaque converts the free sugars in foods and drinks into acids that destroy the tooth over time, that a continued high intake of free sugars, inadequate exposure to fluoride, and a lack of removal of plaque by toothbrushing can lead to caries, pain, and sometimes tooth loss and infection, that untreated dental caries in permanent teeth is the most common health condition in the Global Burden of Disease 2021, that adequate exposure to fluoride is an essential factor in prevention, and that twice daily tooth brushing with fluoride containing toothpaste (1000 to 1500 ppm) should be encouraged. Opened and read first hand on 3 November 2026.