A cavity is a permanently damaged area in a tooth where decay has eaten through the hard outer surface, creating a small hole. Cavities are one of the most common health problems worldwide, and they affect people of all ages. About 26% of adults between 20 and 44 have at least one untreated cavity right now, and roughly 13% of children and teens do too. Understanding how cavities form, what they feel like at different stages, and how they’re treated can help you catch them early, when they’re easiest to fix.
How a Cavity Forms
Your mouth is home to hundreds of species of bacteria. Some of them, particularly one called Streptococcus mutans, feed on sugars and starches left on your teeth after you eat. As these bacteria digest sugar, they produce acid. That acid attacks the minerals in your tooth enamel, the hard, glossy outer layer that protects the softer tissue underneath.
This process is called demineralization, and it happens every time you eat or drink something sugary. Your saliva naturally works to repair some of that damage by depositing minerals back onto the enamel. But when acid attacks happen too frequently, saliva can’t keep up. Over time, the enamel weakens, breaks down, and a hole forms. That hole is a cavity.
Frequency of sugar exposure matters as much as the total amount you consume. Sipping a sugary drink over several hours, for example, bathes your teeth in acid repeatedly. Sticky foods that cling to teeth between meals are especially harmful because they give bacteria a longer window to produce acid.
The Five Stages of Tooth Decay
Cavities don’t appear overnight. They progress through distinct stages, each with different symptoms and treatment options.
Stage 1: White Spots
The earliest sign of trouble is a chalky white spot on the tooth surface. This is where minerals have started leaching out of the enamel. At this point, there’s no actual hole yet, and the damage can sometimes be reversed with fluoride treatments and improved brushing habits. Most people don’t feel anything at this stage.
Stage 2: Enamel Breakdown
If demineralization continues, the white spot may darken to a brownish color and the enamel surface begins to break down. A small hole or pit forms. You still might not feel pain, because enamel has no nerve endings. This is often the stage where a dentist first spots the cavity during a routine exam or on an X-ray.
Stage 3: Decay Reaches the Dentin
Beneath the enamel lies dentin, a softer, yellowish layer that makes up most of the tooth’s structure. Dentin contains tiny tubes that connect to the tooth’s nerve, so once decay breaks through into this layer, you’ll likely start noticing sensitivity. Hot coffee, cold water, or sweet foods may trigger a sharp, fleeting zing. Decay spreads faster through dentin because it’s softer than enamel.
Stage 4: Pulp Damage
The innermost part of the tooth, the pulp, contains blood vessels and nerves. When bacteria reach this area, the pulp becomes inflamed and swollen. Because it’s enclosed in a rigid shell of dentin and enamel, there’s nowhere for the swelling to go. The pressure builds on the nerve, and the result is a deep, throbbing toothache that can be constant rather than triggered only by food or drink.
Stage 5: Abscess
Left untreated, the infection can spread below the tooth and form a pocket of pus called an abscess. This causes severe pain that may radiate into your jaw, ear, or neck. You may also notice swelling in your gums or face, fever, and swollen lymph nodes. A dental abscess is a serious condition. The infection can spread into the jaw bone, sinuses, throat, or even the bloodstream, where it can become life-threatening.
What a Cavity Feels Like
One of the tricky things about cavities is that the early stages are painless. Many people don’t realize they have one until it’s already progressed. Here’s a general timeline of symptoms as decay advances:
- No symptoms at all: Early enamel decay often produces zero pain or sensitivity.
- Sensitivity to temperature or sweets: Once decay hits the dentin, you may wince when drinking something very hot or cold.
- Visible holes or dark spots: You might see or feel a pit in the tooth with your tongue.
- Spontaneous pain: A toothache that shows up without any trigger usually means the pulp is involved.
- Throbbing pain and swelling: Jaw pain, facial swelling, or fever point toward an abscess.
Because early cavities are silent, regular dental checkups are the most reliable way to catch them before they cause pain.
How Dentists Find Cavities
The standard approach is a visual exam combined with dental X-rays, which reveal decay hidden between teeth or beneath the surface. But newer tools can catch cavities even earlier. Laser fluorescence devices shine a specific wavelength of light onto the tooth and measure how much fluorescence bounces back; decayed areas fluoresce differently than healthy enamel. Near-infrared imaging detects differences in how light scatters through sound versus demineralized enamel, without any radiation exposure. These technologies are especially useful for spotting early-stage decay in the grooves of back teeth, where cavities commonly start.
How Cavities Are Treated
Treatment depends entirely on how far the decay has progressed.
For very early white-spot lesions, fluoride treatments (a concentrated gel or varnish applied at the dentist’s office) can help the enamel remineralize and heal itself. No drilling required.
Once a true hole has formed, the standard treatment is a filling. The dentist removes the decayed material and fills the space with a durable material like composite resin (tooth-colored) or amalgam (silver-colored). Fillings are quick, usually done in a single visit, and the tooth functions normally afterward.
When decay is extensive and has weakened a large portion of the tooth, a crown may be needed instead. A crown is a custom-fitted cap that covers the entire visible part of the tooth, restoring its shape and strength. This typically takes two visits: one to prepare the tooth and take impressions, and one to place the permanent crown.
If decay has reached the pulp, a root canal is usually the next step. During this procedure, the infected pulp tissue is removed from inside the tooth, the interior is cleaned and sealed, and the tooth is typically topped with a crown for protection. Despite its reputation, a root canal feels similar to getting a filling, thanks to modern anesthetics. The alternative at this point is extraction.
For abscesses, the immediate priority is clearing the infection, which may involve draining the abscess and a course of antibiotics before the tooth itself can be treated or removed.
What Raises Your Risk
Some people seem more cavity-prone than others, and there are real reasons for that beyond just brushing habits. Frequent snacking and sipping sugary or acidic beverages throughout the day keeps your teeth in a constant state of acid attack. Dry mouth, whether from medications, medical conditions, or simply not drinking enough water, removes one of your best natural defenses because saliva neutralizes acid and helps repair enamel. Teeth with deep grooves and pits trap food and bacteria more easily. And receding gums, common as you age, expose the tooth roots, which lack enamel’s protective hardness and decay more quickly.
Cavity-causing bacteria are also transmissible. Parents can pass Streptococcus mutans to young children through shared utensils or by cleaning a pacifier in their own mouth.
Preventing Cavities
The fundamentals are straightforward: brush twice a day with fluoride toothpaste, floss daily, and limit how often you eat sugary or starchy foods. Standard toothpaste in the U.S. contains 1,000 to 1,100 parts per million (ppm) of fluoride, which is effective for most people. If you’re at higher risk for cavities, toothpaste with 1,500 ppm fluoride has been shown to be slightly more effective. A daily over-the-counter fluoride rinse adds another layer of protection.
Community water fluoridation, which keeps drinking water at 0.7 to 1.2 ppm of fluoride, has been one of the most effective public health measures for reducing cavities across entire populations. If your water isn’t fluoridated (common with well water or certain bottled waters), you miss out on that passive benefit.
Timing matters with your diet. Eating sweets as part of a meal is less damaging than snacking on them between meals, because your mouth produces more saliva during meals. Drinking water after eating helps wash away food particles and dilute acid. And chewing sugar-free gum stimulates saliva flow, which speeds up the natural repair process between meals.