What Does a Cavity Look Like? Every Stage, Where They Hide, and How to Know

You catch something in the mirror: a chalky white patch, a brown spot in a back tooth, or a dark line between two teeth. Or there is nothing to see at all, just a twinge when you drink something cold. Is it a cavity, a stain, or nothing?

Cavities are the most common health condition on the planet, and they rarely look the way people expect. This guide shows what a cavity looks like at each stage, where they hide, how to tell one from a stain, which early ones can still heal, and what the evidence says actually prevents them.

Quick Answer

An early cavity looks like a chalky, matte white spot on the tooth, usually near the gumline or in the grooves of a back tooth. As decay progresses, the spot turns light or dark brown, then black, and finally becomes a visible pit or hole that can catch food or floss. Many cavities form between teeth or under old fillings where you cannot see them at all, and even dental X-rays miss many early lesions. Common signs are sensitivity to sweet, hot or cold, pain when biting, and a toothache, but early cavities often cause no symptoms. A white spot can still be reversed with fluoride; once there is a hole, it needs a dentist. Brushing twice a day with fluoride toothpaste and keeping free sugars under 10 percent of your calories have the strongest evidence for prevention.

In this guide:

• What a Cavity Looks Like, Stage by Stage
• Where Cavities Hide
• Cavity or Stain? How to Tell
• How to Know You Have a Cavity
• Can an Early Cavity Heal?
• How Cavities Are Treated
• What Actually Prevents Cavities
• When to See a Dentist
• The Verdict

What a Cavity Looks Like, Stage by Stage

A cavity is not a sudden hole. It is the end of a slow process called dental caries, in which bacteria in plaque turn sugars into acid, and the acid draws minerals out of the enamel faster than saliva can put them back. It is extraordinarily common: a global analysis found that in 2010 untreated decay in permanent teeth was the single most prevalent health condition in the world, affecting 2.4 billion people, and it peaks three times in life, around ages 6, 25 and 70. The Global Burden of Disease 2021 study put the age-standardized rate at about 27,500 per 100,000 people, more than 1 in 4.

Here is how it typically looks as it progresses:

In older adults, decay also attacks the roots. Where gums have pulled back, the exposed root surface is softer than enamel, and root cavities appear as yellowish-brown, soft-looking areas right at or below the gumline.

Where Cavities Hide

Many cavities never show up in the mirror, because they start in places you cannot see well:

• Between teeth. Decay on the contact surfaces often starts below the point where teeth touch. You might notice floss shredding in one spot, a dark shadow seen through the enamel, or food packing in, but usually nothing at all until it is large.
• The grooves of back teeth. The pits and fissures on the chewing surfaces of molars trap plaque. Decay here can look like a harmless dark line on the surface while spreading wider underneath.
• Along the gumline, especially where brushing is rushed, and around braces brackets and aligner edges, where plaque collects. If you wear aligners, how food and drinks interact with them is covered in can you eat with aligners.
• Under and around old fillings and crowns, where the edge of the restoration meets the tooth.

This is why dentists combine a careful look with X-rays, and why even X-rays are not perfect. A meta-analysis of 117 studies found that radiographs detected only about a quarter to two-fifths of early lesions, and about a third of decay that had reached the dentin between teeth. They were much better at the cavities that matter most for treatment: once a lesion between teeth had become an actual cavity, X-rays picked up more than 60 percent of them and rarely flagged healthy teeth by mistake.

Cavity or Stain? How to Tell

Coffee, tea, red wine, tobacco and some mouthwashes stain teeth, and stains can look worryingly like decay. These clues help, though only a dentist can be sure:

A dark line in a molar groove is the hardest call: it can be harmless staining of a sound groove or decay spreading underneath. If you are unsure, take a photo in good light and show it at your next checkup rather than poking at it, which can damage a weakened spot.

How to Know You Have a Cavity

Early decay is usually silent, which is the main reason regular checkups matter. As a cavity grows, these are the most common signs:

• A sharp twinge when you eat or drink something sweet, cold or hot, in one specific tooth
• Pain when you bite down or chew on one side
• Food catching in the same spot, or floss shredding there
• A rough edge or small hole your tongue keeps finding
• A toothache that comes on by itself, lingers after a cold drink, or wakes you at night, which suggests the decay is close to the nerve
• A bad taste or bad breath that does not go away

Sensitivity on its own is not proof of a cavity. Worn enamel, receding gums, a cracked tooth or recent whitening all cause it too, and sensitivity from whitening usually settles within days; if you whiten while wearing aligners, see whitening your teeth with aligners.

Can an Early Cavity Heal?

Yes, at the white-spot stage. Enamel is constantly losing and regaining minerals: acid pulls them out after you eat, and saliva and fluoride put them back. If the surface has not broken, tipping that balance toward repair can harden the spot again, leaving a lesion that is arrested rather than active. In practice that means fluoride toothpaste twice a day, a fluoride varnish or prescription-strength toothpaste from your dentist if you are at high risk, and fewer sugary snacks and drinks between meals.

Once there is an actual hole, the lost tooth structure does not grow back. Some products online claim to “heal cavities naturally”, but no diet, oil pulling or remineralizing paste rebuilds a cavity that has broken through the enamel. At that stage the aim is to stop it growing and restore the tooth.

How Cavities Are Treated

• Watch and remineralize: for white spots and some early lesions, fluoride varnish, sealing the surface, and checking again at the next visit.
• Filling: the decay is removed and the space filled, usually with tooth-colored composite. Smaller cavities mean smaller fillings, which is the strongest argument for catching them early.
• Crown: when decay has weakened a large part of the tooth.
• Root canal: when decay has reached and infected the nerve, followed by a crown in most back teeth.
• Extraction: when the tooth cannot be saved. A missing tooth can then be replaced with a bridge, a denture or an implant; our dental implant cost calculator gives a realistic price range.
• Silver diamine fluoride (SDF): a liquid painted on to stop decay without drilling, used mostly for young children and older adults. A 2024 Cochrane review found it likely prevents new root decay in older adults and may arrest cavities in baby teeth, though much of the evidence is uncertain. It stains the decayed area permanently black, so it is rarely used on visible front teeth.

What Actually Prevents Cavities

Three measures have strong trial evidence behind them:

• Fluoride toothpaste, twice a day. A Cochrane review of 96 studies found that toothpaste with 1,000 ppm fluoride or more reduces new decay compared with non-fluoride toothpaste in children, adolescents and adults, and 1,450 to 1,500 ppm works slightly better than 1,000 to 1,250 ppm. Check the label, and spit out the excess rather than rinsing with water, so the fluoride stays on your teeth.
• Less sugar, less often. A systematic review for the World Health Organization found moderate-quality evidence that decay is lower when free sugars stay under 10 percent of daily energy; in studies of adults, all five found a link between more sugar and more decay. How often matters as much as how much: sipping a sweet drink over an afternoon keeps your teeth in acid for hours.
• Sealants on children’s back teeth. A thin plastic coating painted into the grooves of permanent molars. In a Cochrane review of 38 trials with 7,924 children, resin sealants reduced decay on those surfaces by between 11 and 51 percent over two years compared with no sealant.

Beyond that: clean between your teeth daily, since that is where your toothbrush cannot reach; keep any aligners or retainers clean, as covered in how to clean your aligners; drink tap water if it is fluoridated where you live; and see a dentist regularly so that white spots are caught while they can still be reversed.

When to See a Dentist

Book an appointment if you notice a spot that has changed color or texture, a hole or rough edge, food trapping in one place, or sensitivity in one tooth that lasts more than a week or two. Go sooner, the same day if you can, for:

• A severe or throbbing toothache, or pain that keeps you awake
• Swelling in the gum, face or jaw, or a pimple-like bump on the gum that may leak fluid, which can mean an abscess
• Fever with tooth pain
• A broken tooth with a sharp or painful edge

Go to an emergency department for facial swelling that is spreading, swelling under the tongue or jaw, or trouble swallowing or breathing. A dental infection can spread quickly and needs urgent treatment.

The Verdict

A cavity starts as a chalky white spot, turns brown or black, and only later becomes a visible hole, and many form between teeth or in molar grooves where you will never see them. Smooth, even staining across several teeth is usually just a stain; a matte, rough or sensitive spot on one tooth deserves a look. White spots can still harden again with fluoride and less frequent sugar, but a hole needs a dentist, and the earlier it is found, the smaller the repair. Fluoride toothpaste twice a day, keeping free sugars under 10 percent of your calories, and sealants for children’s molars are the measures that hold up best in the research.