A cavity is a hole in your tooth created by acid-producing bacteria, and it progresses through distinct stages, from a barely visible white spot on the surface to deep damage that reaches the nerve. Nearly 21% of American adults between 20 and 64 have at least one untreated cavity right now, making it one of the most common chronic health problems. What happens inside your tooth, how fast it moves, and what you’ll actually experience depends on how far along the decay has gotten.
How a Cavity Forms
Your mouth is home to hundreds of species of bacteria. Some of them feed on sugars and starches left on your teeth after eating, and they produce organic acids as a byproduct. Those acids dissolve the minerals that make up your enamel, the hard outer shell of each tooth. This process is called demineralization, and it’s happening on a small scale every time you eat.
Normally, your saliva works to redeposit minerals back into the enamel, balancing things out. But when acid attacks happen too frequently (from snacking, sugary drinks, or poor brushing habits), the balance tips. Minerals leave faster than they return, and the enamel starts to break down. That’s when a cavity begins.
The Stages of Tooth Decay
Cavities don’t appear overnight. In most cases, they develop over months to years, depending on your diet and oral hygiene. The progression follows a predictable path through the layers of your tooth.
Stage 1: White Spot (Demineralization)
The earliest sign is a chalky white spot on the tooth’s surface where minerals have been lost. At this point, there’s no actual hole yet. You won’t feel any pain or sensitivity. This is the only stage where the damage can be fully reversed: fluoride from toothpaste, drinking water, or professional treatments helps your enamel absorb minerals from saliva and rebuild itself. No filling required.
Stage 2: Enamel Decay
If demineralization continues, the enamel breaks down enough to form tiny openings or pits. This is the first true cavity. You still might not feel anything, since enamel has no nerve endings. You may notice brown, black, or white staining on the tooth surface. At this stage, a dentist typically treats the cavity with a filling.
Stage 3: Dentin Decay
Beneath your enamel sits a softer layer called dentin. Once bacteria and acid break through the enamel, they chew through dentin much faster because it’s less resistant to acid. This is usually when you start noticing symptoms: sensitivity to hot, cold, or sweet foods and drinks, along with mild to sharp pain. The cavity is growing more quickly now, and a filling or crown is needed depending on how much tooth structure has been lost.
Stage 4: Pulp Damage
At the center of every tooth is the pulp, a soft tissue containing nerves and blood vessels. When decay reaches the pulp, bacteria cause it to swell. Because the pulp is enclosed inside a rigid tooth, there’s nowhere for the swelling to go. The nerve gets compressed, producing significant, persistent pain. Treatment at this stage requires a root canal, a procedure that removes the infected pulp, cleans the interior of the tooth, and seals it.
Stage 5: Abscess
If pulp infection goes untreated, bacteria can push past the tooth root and form a pocket of pus called an abscess. This causes throbbing pain, swelling in the jaw or face, and sometimes fever. An abscess needs prompt treatment, typically a root canal or extraction, to drain the infection and prevent it from spreading.
What It Actually Feels Like
One of the tricky things about cavities is that early ones produce no symptoms at all. Many people don’t realize they have one until a dentist spots it on an X-ray. As the decay deepens, symptoms tend to appear in a fairly predictable order:
- Sensitivity: A brief zing when you drink something cold or eat something sweet, usually the first noticeable sign.
- Visible changes: Holes, pits, or dark spots on the tooth that you can see or feel with your tongue.
- Spontaneous pain: A toothache that shows up without any obvious trigger, often signaling that the decay has reached deeper layers.
- Pain when biting: Discomfort when you chew or press your teeth together, suggesting structural damage to the tooth.
If you’re experiencing sharp, constant pain or swelling around a tooth, the decay has likely progressed well past the enamel.
How Dentists Find Cavities
During a checkup, your dentist uses a combination of visual examination and X-rays. Cavities between teeth are especially hard to see with the naked eye. Bitewing X-rays, the kind where you bite down on a small tab, are specifically designed to reveal decay between teeth and below the gum line. Periapical X-rays capture the full tooth from crown to root and can detect cavities near the root, bone loss, and abscesses. This is why regular dental visits catch cavities that you’d never notice on your own.
How Cavities Are Treated
The treatment depends entirely on how deep the decay goes.
For small to moderate cavities that haven’t reached the pulp, a filling is the standard fix. The dentist removes the decayed portion and fills the space with a material that restores the tooth’s shape. Composite (tooth-colored) fillings last about 5 to 7 years on average, while amalgam (silver) fillings typically hold up for 10 to 15 years. Both can last longer with good care.
When decay is extensive and has weakened a large portion of the tooth, a crown may be placed over the entire tooth to protect what’s left. If decay has reached the pulp, a root canal cleans out the infection from the tooth’s interior and seals it, usually followed by a crown. In the worst cases, where the tooth can’t be saved, extraction is the final option.
What Happens If You Ignore It
A cavity won’t heal on its own once it’s past the white-spot stage. Left alone, it will keep growing. The timeline varies, but the direction is always the same: deeper into the tooth, closer to the nerve, and eventually into the surrounding bone and tissue.
The most serious risk of an untreated cavity is a dental abscess. Beyond causing intense pain and facial swelling, the infection can spread to the jaw, sinuses, and other areas of the head and neck. In rare but real cases, an untreated abscess can lead to sepsis, a life-threatening whole-body infection. People with weakened immune systems face an even higher risk of these complications. A tooth that could have been saved with a simple filling can eventually require a root canal, extraction, or emergency treatment for a spreading infection.
Slowing and Preventing Decay
Because cavities are driven by acid production from bacteria feeding on sugars, prevention comes down to disrupting that cycle. Brushing twice a day with fluoride toothpaste removes the bacterial film (plaque) before it can do significant damage. Flossing clears plaque from between teeth where brushes can’t reach, exactly the spots where hidden cavities tend to form.
Limiting how often you snack or sip sugary drinks matters more than the total amount of sugar you consume. Every time sugar hits your teeth, bacteria produce acid for about 20 to 30 minutes. Frequent snacking means your teeth are under near-constant acid attack, and your saliva never gets a chance to repair the damage. Drinking water, especially fluoridated tap water, helps wash away food particles and supports remineralization throughout the day.