A cavity starts small and painless, but left alone, it gradually eats through your tooth’s layers and can eventually cause serious pain, infection, and tooth loss. About 21% of American adults have at least one untreated cavity right now, making this one of the most common chronic health problems in the country. Understanding what actually happens inside your tooth helps you recognize when to act and what to expect if you don’t.
How a Cavity Forms and Grows
A cavity doesn’t appear overnight. It begins as a patch of weakened enamel called a white spot lesion, where acids from bacteria have started dissolving the minerals in your tooth’s outer shell. At this point, there’s no hole yet. The surface is still intact, and the damage is potentially reversible with fluoride and good oral care.
If the mineral loss continues, the enamel breaks down enough to create an actual hole, a break in the tooth’s surface. This is the point most people think of as “getting a cavity.” Once that outer barrier is breached, things speed up. Beneath your enamel sits dentin, a softer, more porous layer that bacteria can move through much more easily. Decay that took months or years to push through enamel can spread faster once it hits dentin.
At the center of every tooth is the pulp, a chamber containing nerves and blood vessels. When bacteria reach the pulp, it becomes inflamed and swollen. Because the pulp is sealed inside a hard shell with nowhere to expand, the swelling presses directly on the nerve. That’s when the real pain starts. In most cases, this level of damage takes years of neglect, though poor oral hygiene or a high-sugar diet can accelerate the timeline significantly.
What You’ll Feel at Each Stage
Early cavities are sneaky. When decay is still confined to the enamel, you’ll likely feel nothing at all. There’s no pain, no sensitivity, and no visible hole. You might notice a chalky white or yellowish-brown spot on the tooth, but many people miss it entirely. This is why regular dental checkups catch cavities that you wouldn’t find on your own.
As the cavity grows deeper, symptoms start showing up. You may notice mild to sharp pain when eating or drinking something sweet, hot, or cold. Biting down on that tooth might feel uncomfortable. You could see visible pits, holes, or dark staining on the tooth surface. These symptoms come and go at first, which leads many people to put off treatment.
Once decay reaches the pulp, the pain changes character. Instead of brief jolts triggered by food or temperature, you may experience a persistent, throbbing toothache that wakes you up at night or lingers for hours. At this stage, the nerve inside the tooth is inflamed or dying, and simple fixes like fillings are no longer enough.
What Happens If You Ignore It
An untreated cavity doesn’t plateau. Bacteria continue pushing deeper until they reach the root tip, where infection can form a pocket of pus called an abscess. A dental abscess causes intense, radiating pain and often visible swelling in the gums or face. It can also cause fever, a foul taste in your mouth, and swollen lymph nodes in your neck.
The infection doesn’t necessarily stay put. It can spread into the jawbone, and if the affected tooth is near your upper sinuses (the air-filled spaces behind your cheeks), the abscess can create a connection between the tooth and the sinus cavity, triggering a sinus infection. In more serious cases, the infection spreads to the head, neck, or throat. Difficulty breathing or swallowing alongside facial swelling is a medical emergency.
In rare but real scenarios, an untreated dental infection leads to sepsis, a life-threatening condition where infection enters the bloodstream and triggers a dangerous immune response throughout the body. People with weakened immune systems face a higher risk of these complications.
Cavities in Children’s Baby Teeth
A common misconception is that cavities in baby teeth don’t matter because those teeth fall out anyway. They do matter. Untreated decay in primary teeth causes pain and infections that can interfere with eating, speaking, and learning. About 18% of children ages 6 to 8 have untreated cavities in their baby teeth. Baby teeth also serve as placeholders for permanent teeth. Losing them early to infection or extraction can cause spacing problems that affect how adult teeth come in.
How Dentists Find Cavities
Visual exams catch obvious cavities, but a lot of decay hides between teeth or beneath the surface where it can’t be seen. Dental X-rays remain the standard tool for spotting these hidden problems, revealing dark shadows in the tooth structure that indicate mineral loss.
Some dental offices also use laser fluorescence devices that shine a low-intensity laser on the tooth surface. Healthy enamel and decayed enamel reflect this light differently, and the device gives a numeric reading that flags areas of concern. These tools are especially useful for catching very early decay before it becomes a full cavity. Dentists typically combine laser readings with X-rays and a visual exam to confirm findings, since staining or minor enamel irregularities can occasionally trigger false positives.
How Cavities Are Treated
Treatment depends entirely on how far the decay has progressed.
For small to moderate cavities, a filling is the standard fix. Your dentist removes the decayed portion of the tooth and fills the space with a material like composite resin (tooth-colored), amalgam (silver-colored), or glass ionomer. This is done in a single visit and is one of the most routine procedures in dentistry.
When a cavity is too large for a standard filling but hasn’t reached the pulp, your dentist may recommend an inlay or onlay. These are custom-made restorations, sometimes crafted from porcelain or gold, that fit into the remaining tooth structure like a puzzle piece. Depending on the technology your dentist uses, this takes one or two appointments. If the tooth has lost significant structure, a crown (a cap that covers the entire visible portion of the tooth) may be necessary instead.
Once decay reaches the pulp, a root canal is the only way to save the tooth. The infected pulp tissue is removed, the interior of the tooth is cleaned and sealed, and a crown is placed over the top to protect what remains. If the tooth is too damaged even for that, extraction is the last resort.
Connections to Broader Health
Oral infections don’t exist in isolation from the rest of your body. Research has consistently found that people with poor oral health, including gum disease and tooth loss, have higher rates of cardiovascular problems like heart attack and stroke. The connection likely involves inflammation: bacteria from oral infections can enter the bloodstream, triggering an immune response that damages blood vessels elsewhere in the body.
The relationship is complicated, though. A large study analyzing data from nearly a million people found that when smoking was accounted for, the link between tooth loss and heart disease largely disappeared. This suggests that shared risk factors like smoking and poor diet may partly explain why oral and cardiovascular disease tend to appear together. Still, chronic oral infections create a sustained inflammatory burden that your body has to manage, and reducing that burden is one more reason to treat cavities before they become something worse.