Dental caries, commonly called cavities or tooth decay, are permanently damaged areas in the hard surface of your teeth that develop into tiny holes. They are the most common chronic infectious disease in children and affect an estimated 2.5 billion people worldwide in their permanent teeth alone, according to the World Health Organization. Caries form when bacteria on your teeth feed on sugars and produce acids that eat away at tooth enamel over time.
How Cavities Form
Your mouth naturally contains hundreds of bacterial species, but a few are especially good at causing decay. The primary culprits are bacteria called Streptococcus mutans, Streptococcus sobrinus, and lactobacilli. These organisms thrive on fermentable carbohydrates like glucose, sucrose, and fructose. When you eat or drink something sugary, these bacteria break down the sugars and produce lactic acid as a byproduct.
That acid lowers the pH on your tooth surface, and when it drops below about 5.5, a chemical process begins. The acid reacts with phosphate and carbonate in your enamel’s mineral structure, pulling calcium and other minerals out of the tooth. This is called demineralization. Your saliva normally acts as a buffer, neutralizing the acid and washing minerals back onto the tooth surface. It takes roughly 20 minutes for saliva to bring the pH back to safe levels after each sugar exposure. If you snack or sip sugary drinks frequently throughout the day, your saliva never gets that recovery window, and mineral loss outpaces mineral gain.
Stages of Tooth Decay
Cavities don’t appear overnight. They progress through distinct stages, and catching them early makes a real difference in how they’re treated.
White spot lesion: The earliest visible sign is a chalky white or yellowish patch on the enamel, usually near the gum line. At this point, the surface is still intact. Mineral loss is happening beneath the surface, but the tooth hasn’t broken down yet. These lesions are often covered by plaque, which is why they’re easy to miss. This stage is reversible.
Enamel breakdown: If the acid attacks continue, the enamel becomes increasingly porous and small microcavities form in the surface. You might not feel anything at this point because enamel has no nerve endings.
Dentin involvement: Once decay punches through the enamel, it reaches the softer dentin layer underneath. Dentin is less minerite-dense and contains tiny tubes that connect to the tooth’s nerve. This is typically when you start noticing sensitivity to hot, cold, or sweet foods. The tooth tries to protect itself by producing a layer of new dentin near the pulp, but it can’t keep up with aggressive decay.
Pulp infection: If decay reaches the innermost pulp chamber, where the nerve and blood vessels live, it causes inflammation (pulpitis). This is when a toothache can become severe and persistent. At this point, a simple filling is no longer enough, and a root canal or extraction is usually necessary.
Abscess: Left untreated further, the infection can spread beyond the tooth into the jawbone and surrounding tissues, forming a painful abscess.
Why Some People Get More Cavities
Diet is the most obvious factor, but it’s not just about how much sugar you eat. How often you eat it matters more. Each sugary snack or drink triggers a fresh 20-minute acid attack. Someone who sips soda throughout the afternoon exposes their teeth to far more cumulative acid than someone who drinks the same amount in one sitting with a meal.
Saliva flow plays a major protective role. Normal salivary flow buffers acid, washes away food debris, and delivers calcium and phosphate back to the enamel. Anything that reduces saliva production raises your risk significantly. Hundreds of common medications, including antihistamines, antidepressants, and blood pressure drugs, list dry mouth as a side effect. Medical conditions like Sjögren’s syndrome and radiation therapy to the head and neck can reduce saliva to dangerously low levels, dramatically increasing the chance of rapid decay.
Older adults face a unique risk because gum recession exposes root surfaces that were never designed to withstand direct acid exposure. Root surfaces lack the thick enamel shield that protects the crown of the tooth, so they decay faster. Research shows that people with root caries tend to have higher counts of decay-causing bacteria and weaker salivary buffering capacity.
Reversing Early Decay
The most important thing to understand about dental caries is that the earliest stage, the white spot lesion, can actually be reversed. Because the enamel surface is still intact, minerals can be redeposited into the weakened subsurface layer through a process called remineralization.
Fluoride is the most well-established remineralization agent. When fluoride is present during an acid attack, it integrates into the enamel structure and forms fluorapatite, a mineral that’s more resistant to acid than the original enamel. This is why fluoride toothpaste (typically containing 1,000 to 1,500 ppm fluoride) is the foundation of cavity prevention. For people at higher risk, dentists may recommend prescription-strength fluoride toothpaste, fluoride mouth rinses (available in daily-use or weekly-use concentrations), professional fluoride varnishes, or fluoride gel treatments applied in the office.
A newer option is products containing casein phosphopeptide-amorphous calcium phosphate, often sold as tooth mousse or cream. These release calcium and phosphate directly into the biofilm on your teeth, keeping the local environment rich in the minerals needed for repair. When combined with fluoride, research shows this approach is especially effective for people with high caries activity.
How Cavities Are Treated
Once a cavity has progressed past the white spot stage and actual tooth structure has been lost, the damage can’t be reversed. Treatment depends on how far the decay has spread. Small to moderate cavities are cleaned out and filled, typically with tooth-colored composite resin. Larger cavities that have destroyed significant tooth structure may need a crown to restore strength. When decay reaches the pulp, root canal therapy removes the infected tissue and seals the tooth. In the most severe cases, extraction is the only option.
For cavities in young children, older adults, or people who have difficulty tolerating traditional dental procedures, a treatment called silver diamine fluoride (SDF) offers a noninvasive alternative. Applied as a liquid directly to the cavity, SDF arrests approximately 80% of treated lesions. A large analysis found that 81% of cavities in baby teeth treated with SDF were successfully arrested over follow-up periods of 6 to 30 months. Twice-yearly application at a 38% concentration works best. The main trade-off is cosmetic: SDF permanently stains the decayed area black. It’s not appropriate for teeth with suspected pulp involvement or for anyone with a silver allergy.
What Happens When Decay Is Ignored
Untreated dental caries can escalate well beyond a toothache. As infection spreads from the tooth into surrounding tissues, it can cause facial cellulitis (a spreading soft-tissue infection) or deep neck infections, including abscesses in the spaces around the throat. These are medical emergencies. Without timely treatment, deep neck infections can lead to airway obstruction, blood clot formation in the jugular vein, infection spreading into the chest cavity, or sepsis.
The consequences aren’t limited to the mouth and neck. Chronic oral infections have been linked to cardiovascular disease and infective endocarditis, an infection of the heart’s inner lining. Beyond these acute risks, untreated decay leads to tooth loss, difficulty chewing, nutritional problems, and significant impacts on appearance and quality of life.
Prevention That Actually Works
Brushing twice a day with fluoride toothpaste and flossing daily remain the most effective habits for preventing caries. The mechanical removal of plaque disrupts bacterial colonies before they can produce enough acid to cause damage. Community water fluoridation, maintained at the CDC-recommended concentration of 0.7 milligrams per liter, provides a constant low-level fluoride exposure that supports remineralization throughout the day.
Dietary habits matter as much as oral hygiene. Limiting the frequency of sugar exposure, rather than just the total amount, gives your saliva time to neutralize acid between meals. Drinking water instead of soda or juice between meals, finishing sweets as part of a meal rather than as standalone snacks, and chewing sugar-free gum to stimulate saliva flow are all practical strategies. For people with dry mouth, staying hydrated, using saliva substitutes, and discussing medication alternatives with a doctor can help restore some of saliva’s protective function.