A cavity is a hole in your tooth created by acid-producing bacteria that slowly dissolve the hard outer layers. Nearly 21% of adults between 20 and 64 have at least one untreated cavity right now, according to CDC surveillance data. The process doesn’t happen overnight. It moves through distinct stages, each one deeper and more painful than the last, and understanding those stages helps you recognize what’s going on in your mouth before things get serious.
How a Cavity Actually Forms
Your mouth is home to hundreds of bacterial species, and some of them feed on the sugars and starches you eat. As they digest those carbohydrates, they produce organic acids, primarily lactic acid. These acids pool against your tooth surface inside the sticky film of plaque that builds up throughout the day. When the acid concentration gets high enough, it starts pulling minerals out of your enamel, the hard outer shell of the tooth. This process is called demineralization.
The bacteria don’t just produce acid once and stop. They create a low-pH environment that attracts other acid-loving species, building a kind of bacterial ecosystem that keeps the acid levels elevated. The longer plaque sits on a tooth surface undisturbed, the more sustained the acid attack becomes. This is why the spots where your toothbrush and floss can’t easily reach, like the grooves on your molars or the tight spaces between teeth, are where cavities tend to start.
The Five Stages of Decay
Cavities progress through a predictable sequence, and the symptoms change at each stage.
Stage 1: White Spots
The first sign is a chalky white spot on the tooth surface. This is where minerals have started leaching out of the enamel but no actual hole has formed yet. You won’t feel any pain at this point, and you probably won’t notice it unless your dentist points it out or it’s on a front tooth. This is the only stage where the damage is fully reversible. Your saliva naturally carries calcium and phosphate that can rebuild weakened enamel, and fluoride from toothpaste accelerates that repair process.
Stage 2: Enamel Breakdown
If remineralization can’t keep up with the acid damage, the enamel surface breaks down and a physical hole forms. Once there’s an actual cavity in the enamel, your body can no longer repair it on its own. That’s the hard line: a white spot can heal, but a hole cannot. At this stage you still may not feel much, since enamel has no nerve endings. A dentist would typically treat this with a standard filling.
Stage 3: Dentin Decay
Beneath the enamel sits dentin, a softer, yellowish layer that makes up most of the tooth’s structure. Dentin is riddled with microscopic tubes that run from the outer surface straight down to the nerve-rich core of the tooth. When decay reaches dentin, those tiny tubes act as hydraulic channels. Hot coffee, cold water, or even air passing over the tooth creates fluid movement inside the tubes, which triggers the nerve endings at the other end. This is when sensitivity and pain begin, and the decay accelerates because dentin is much softer and less mineral-dense than enamel.
Stage 4: Pulp Infection
The innermost part of your tooth, the pulp, contains the nerves and blood vessels that kept the tooth alive as it was developing. When bacteria reach this chamber, the pulp becomes inflamed and begins to swell. But unlike swollen tissue elsewhere in your body, the pulp is trapped inside a rigid shell of dentin and enamel with nowhere to expand. That pressure on the nerve is what produces the deep, throbbing toothache that can radiate into your jaw, ear, or the side of your head. At this point a simple filling won’t work. The infected pulp tissue needs to be removed through a root canal to save the tooth.
Stage 5: Abscess
If pulp infection goes untreated, bacteria can push past the tip of the tooth’s root and into the surrounding jawbone, forming a pocket of pus called an abscess. The symptoms are hard to ignore: severe, constant throbbing pain, swelling in the face or neck, fever, swollen lymph nodes under the jaw, and sometimes a foul taste if the abscess ruptures and drains into the mouth. An abscess is a genuine medical concern because the infection can spread to the jaw, the sinus cavities behind your cheekbones, or deeper into the neck and throat. In rare but serious cases, it can enter the bloodstream and cause sepsis.
Why You Might Not Feel It at First
One of the most common surprises about cavities is that the early stages are completely painless. Enamel contains no nerves, so a cavity can grow for months while you eat, drink, and brush without noticing anything wrong. Many people first learn they have a cavity from a dental X-ray, not from pain. By the time a cavity actually hurts, it has usually already reached the dentin or deeper. This is the main reason regular dental checkups catch problems that you physically can’t feel yet.
Sensitivity to hot, cold, or sweet foods is often the first symptom people notice on their own. That sensitivity means the decay has broken through the enamel and is affecting the dentin layer underneath. A persistent, unprompted toothache, one that shows up without eating or drinking anything, typically signals that the pulp is involved.
How Cavities Are Treated at Each Stage
Treatment depends entirely on how deep the decay has gone. An early white spot lesion can sometimes be reversed with fluoride treatments and improved oral hygiene, no drilling required. Once a physical hole has formed in the enamel or dentin, a filling is the standard fix. The dentist removes the decayed material and fills the space with a composite resin or similar material. This is the most common cavity treatment, and it’s typically done in a single visit with local numbing.
When the cavity is large enough that a filling would leave too little healthy tooth structure behind, a crown is used instead. A crown covers and protects the entire visible portion of the tooth. If decay has reached the pulp, a root canal removes the infected tissue from inside the tooth, and the cleaned-out space is sealed. The tooth is then usually capped with a crown to restore its strength. If the tooth is too damaged to save at all, extraction becomes the final option.
How Fast Cavities Progress
There’s no single timeline that applies to everyone. A cavity’s speed depends on factors like how much sugar you eat, how acidic your saliva is, whether you use fluoride, how well you clean your teeth, and even the specific bacteria living in your mouth. In general, the journey from a white spot through the enamel can take many months to a couple of years. Once decay hits the softer dentin layer, it tends to spread faster. Some cavities between teeth can grow for a year or more before they’re large enough to show up on an X-ray or cause symptoms.
Children’s baby teeth have thinner enamel than adult teeth, which is why cavities in young kids can progress more quickly. About 18% of children aged 6 to 8 have untreated decay in their baby teeth, making it one of the most common childhood health issues.
What Makes Some People More Cavity-Prone
Cavities aren’t just about brushing habits. The shape of your teeth matters: deep grooves and tight contact points between teeth create sheltered spots where plaque accumulates. Dry mouth, whether from medication, mouth breathing, or a medical condition, removes one of your mouth’s best natural defenses, since saliva neutralizes acid and delivers minerals back to your enamel. A diet high in sugar or frequent snacking keeps acid levels elevated for longer stretches of the day, giving bacteria more fuel. Even the composition of your oral bacteria varies from person to person, and some people harbor more aggressive acid-producing strains than others.
Fluoride exposure plays a significant protective role. Fluoride integrates into enamel and makes it more resistant to acid attacks. People who drink unfluoridated water and don’t use fluoride toothpaste consistently face a higher risk of decay, all other factors being equal.