Holes in teeth are caused by acid dissolving the hard mineral structure of your enamel. In most cases, that acid comes from bacteria living in your mouth, but acidic foods, drinks, and even stomach acid can do the same damage. About one in four American adults has at least one untreated cavity right now, making this one of the most common chronic health problems worldwide.
How Bacteria Create Cavities
Your mouth is home to hundreds of bacterial species, but one in particular drives most cavities: Streptococcus mutans. This bacterium feeds on sugars and starches left on your teeth after eating, then excretes acid as a waste product. The acid it produces, primarily lactic acid, is strong enough to dissolve the minerals that make up tooth enamel.
Enamel is 96% mineral and is the hardest tissue in your body, but it has a specific vulnerability. When the environment around a tooth drops below a pH of about 5.5, enamel minerals begin to dissolve. For context, pure water has a pH of 7, so this threshold isn’t extremely acidic. Every time you eat something sugary or starchy, bacteria on your teeth produce enough acid to cross that line for 20 to 30 minutes.
These bacteria don’t work alone. They build a sticky film called biofilm (what you feel as plaque) that clings to tooth surfaces and traps acid right against the enamel. The biofilm also creates a sheltered environment where acid-tolerant bacteria thrive and outcompete healthier oral microbes. Over time, with repeated sugar exposure, the bacterial community in plaque shifts to become increasingly acidic, making decay more likely with each cycle.
What Dissolves Teeth Without Bacteria
Not all holes and wear come from cavities. Dental erosion is the loss of tooth structure caused by acids that don’t come from mouth bacteria, and it can thin enamel or create pitting and craters on tooth surfaces.
The most common extrinsic cause is frequent consumption of acidic drinks. Soft drinks, sports drinks, and fruit juices typically have pH values between 2.0 and 3.5, well below the 5.5 threshold where enamel dissolves. Research shows that regular soft drink consumption more than doubles the risk of erosion. Chewable vitamin C tablets, sour candies, and acidic snacks also contribute.
Intrinsic causes involve your own stomach acid reaching your teeth. GERD (acid reflux) is a major one. Gastric acid that rises into the mouth during sleep is especially damaging because saliva flow drops at night and can’t buffer the acid effectively. In a lying-down position, the acid can pool around back teeth for extended periods. Bulimia nervosa causes even more severe erosion: over 90% of people with bulimia show erosive damage, particularly on the backs of the front teeth where stomach acid hits during vomiting. Chronic alcoholism and severe pregnancy-related vomiting can produce similar effects.
Even environmental exposures play a role. Factory workers around airborne industrial acids and competitive swimmers in heavily chlorinated pools show higher rates of erosion.
The Five Stages of Decay
A cavity doesn’t appear overnight. Most develop over months to years, and the process follows a predictable path through the layers of your tooth.
Stage 1: White spots. The earliest sign is a chalky white spot or line on the enamel, usually near the gum line. This is demineralization, meaning minerals are leaving the enamel surface, but no actual hole has formed yet. This stage is reversible.
Stage 2: Enamel breakdown. If demineralization continues, the white spot darkens to brown and the enamel surface begins to break down. A small hole forms. You probably won’t feel anything at this point because enamel has no nerves.
Stage 3: Dentin decay. Beneath the enamel sits dentin, a softer tissue with tiny tubes that connect to the nerve of the tooth. Once decay reaches dentin, it speeds up because dentin dissolves more easily. This is when you start noticing sensitivity to hot, cold, or sweet foods.
Stage 4: Pulp involvement. The pulp is the innermost part of the tooth, containing nerves and blood vessels. When bacteria reach it, the pulp swells, but because it’s enclosed in hard tissue, the swelling has nowhere to go. The pressure on nerves creates significant, sometimes constant, pain.
Stage 5: Abscess. An untreated infection at the pulp can spread to the bone beneath the tooth, forming a pocket of pus called an abscess. This causes severe pain that can radiate into the jaw, along with swelling of the gums or face, fever, and swollen lymph nodes.
Why Some People Get More Cavities
Diet is the single biggest controllable factor. The more frequently you eat sugary or starchy foods, the more often bacteria produce acid, and the less time your teeth have to recover between acid attacks. It’s the frequency that matters most, not just the total amount. Sipping a soda over two hours is harder on your teeth than drinking it in five minutes because it extends the window of acid exposure.
Saliva is your mouth’s primary defense. It rinses away food particles, neutralizes acid, and delivers minerals back to weakened enamel. Anything that reduces saliva flow increases cavity risk. Dry mouth from medications (antihistamines, antidepressants, blood pressure drugs, and many others), mouth breathing, dehydration, or medical conditions affecting the salivary glands all leave teeth more vulnerable. Teeth that are least protected by saliva, like upper front teeth, tend to develop cavities first.
Tooth anatomy matters too. Deep grooves on the chewing surfaces of molars trap food and bacteria in spots a toothbrush can’t easily reach. Crowded or overlapping teeth create tight contact points that are hard to clean. And teeth with naturally thinner enamel, whether from genetics or developmental issues, have less of a protective buffer before decay reaches dentin.
How Early Damage Reverses Itself
Your teeth aren’t passive targets. Between acid attacks, saliva works to repair enamel in a process called remineralization. As saliva brings the pH back up above 5.5, calcium and phosphate ions from saliva redeposit into the weakened enamel surface.
Fluoride supercharges this process. When fluoride is present in saliva during remineralization, it incorporates into the enamel crystal structure, creating a form of the mineral that is harder and more acid-resistant than what was originally there. This is why fluoride toothpaste and fluoridated water are effective: they don’t just prevent cavities, they help repair the earliest stages of damage. White spot lesions, the first visible sign of decay, can be fully reversed with consistent fluoride exposure and improved oral hygiene.
The catch is timing. Once a physical hole forms in the enamel, remineralization can no longer rebuild the lost structure. At that point, only a dental restoration can fix the damage. This is why catching decay early matters so much. A white spot is a warning sign, not a death sentence for the tooth.
How Long a Cavity Takes to Form
There’s no universal timeline because it depends entirely on the balance between acid attacks and repair. In someone with good oral hygiene, moderate sugar intake, and adequate saliva flow, a cavity can take years to progress through enamel. In someone with poor hygiene, frequent snacking, and dry mouth, the same process can happen in months.
Once decay passes through enamel into dentin, it accelerates. Dentin is softer and more porous, so bacteria and acid spread faster. The jump from dentin involvement to pulp damage can happen more quickly than the initial enamel breakdown took, which is why a tooth that seemed fine at one checkup can need significant treatment at the next.