A cavity is a permanently damaged area in the hard surface of a tooth, forming a small hole where decay has eaten through. Cavities are one of the most common health problems worldwide. According to CDC data, nearly 21% of U.S. adults between 20 and 64 have at least one untreated cavity right now, and about 11% of children as young as 2 to 5 already have decay in their baby teeth.
How Cavities Form
Your mouth is home to hundreds of species of bacteria. When you eat or drink something containing sugar or starch, bacteria feed on those carbohydrates and produce acid as a byproduct. That acid attacks your enamel, the hard outer shell of your tooth. Each time you eat, this “acid attack” lasts for about 20 minutes before your saliva can neutralize it.
If these acid attacks happen frequently enough, your enamel loses minerals faster than it can rebuild them. Over time, the enamel weakens and breaks down, creating a hole. That hole is the cavity. Left alone, the decay moves deeper, passing through the enamel into the softer layer underneath called dentin, and eventually into the innermost part of the tooth where the nerve lives.
Early Decay Can Actually Be Reversed
Before a full cavity forms, there’s a stage where the enamel has lost minerals but hasn’t broken through yet. This often shows up as a white spot on the tooth. At this point, the damage is reversible. Your saliva naturally carries calcium and phosphate that help rebuild weakened enamel, and fluoride from toothpaste or drinking water accelerates this repair process.
The catch is that your teeth need time between acid attacks to heal. If you’re snacking frequently throughout the day, your enamel never gets that recovery window. Limiting between-meal snacks is one of the simplest ways to give your teeth a chance to repair early damage before it becomes a permanent cavity.
What a Cavity Feels Like
Early cavities often cause no symptoms at all. This is why many people have cavities without knowing it. As the decay grows larger, you may notice:
- A toothache or spontaneous pain with no obvious trigger
- Sensitivity to sweet, hot, or cold foods and drinks, ranging from mild to sharp
- Pain when you bite down
- Visible holes or pits in a tooth
- Brown, black, or white staining on any surface of a tooth
The location matters too. A cavity between two teeth might cause no visible signs but can trigger pain when food gets packed into the gap. A cavity on a chewing surface might be easier to spot but may not hurt until it’s fairly deep. By the time a cavity causes consistent pain, the decay has usually progressed well past the enamel.
Risk Factors Beyond Sugar
Sugar gets most of the blame, and it deserves a lot of it. But several other factors raise your risk in ways that aren’t as obvious.
Dry mouth is a major one. Saliva is your teeth’s natural defense, washing away food particles and delivering the minerals that repair enamel. Anything that reduces saliva flow increases cavity risk significantly. Hundreds of common medications, including antihistamines, antidepressants, and blood pressure drugs, list dry mouth as a side effect. Coffee, tea, and alcohol can also dry out your mouth.
Some people are born with thinner or weaker enamel, a condition called enamel hypoplasia. This can result from a vitamin D deficiency during pregnancy, certain genetic conditions, or childhood infections that disrupted tooth development. If your enamel is naturally thinner, it takes less acid exposure to create a cavity.
Where your teeth sit in your mouth matters too. Back teeth (molars) have grooves and crannies that trap food and are harder to clean. They develop cavities far more often than smooth-surfaced front teeth.
How Cavities Are Treated
Treatment depends entirely on how deep the decay has gone.
When decay is limited to the outer layers of the tooth, a filling is the standard fix. Your dentist removes the decayed portion and fills the space with a material like composite resin or amalgam. This is the most common cavity treatment, and it’s straightforward. You’re typically numb for the procedure and back to normal within a few hours.
If the cavity is large enough that a filling wouldn’t leave enough healthy tooth structure to hold up, a crown (a cap that covers the entire visible tooth) may be needed instead. This requires more preparation but still preserves the tooth.
When decay reaches the innermost part of the tooth where the nerve and blood vessels live, the situation is more serious. Deep, throbbing pain, swelling, or prolonged sensitivity to temperature are signs the nerve may be affected. At this stage, a root canal becomes necessary. The infected tissue inside the tooth is removed, the interior is cleaned and sealed, and a crown is placed over it to restore strength. Without treatment, the infection can spread to the bone and surrounding tissue.
If decay has destroyed too much of the tooth for any of these options, extraction is the last resort.
Who Gets Cavities Most Often
Cavities affect every age group, but the patterns shift across life. Nearly 18% of children aged 6 to 8 have untreated decay in their baby teeth. That number drops to about 10% in adolescents aged 12 to 19, likely reflecting a combination of better brushing habits and access to dental care during school years. Adults aged 20 to 64 have the highest rate at nearly 21%, while adults 65 and older come in at about 13%.
The high rate in working-age adults reflects several converging factors: gaps in dental insurance, busy schedules that push dental visits down the priority list, and the cumulative effect of decades of acid attacks. Older adults often face cavity risk in a different spot, around the gum line, where receding gums expose the softer root surface of the tooth.
Preventing Cavities
Fluoride toothpaste twice a day is the single most effective habit. Fluoride doesn’t just strengthen enamel; it actively helps rebuild areas that have started to weaken. Brushing before bed is especially important because saliva flow drops while you sleep, leaving your teeth more vulnerable overnight.
Flossing cleans the surfaces between teeth where a toothbrush can’t reach, and those tight spaces between molars are prime territory for cavities. Reducing how often you eat sugary or starchy snacks matters more than reducing how much sugar you eat in one sitting, because each snack triggers a fresh acid attack. Drinking water throughout the day, particularly fluoridated tap water, helps wash away food particles and keeps saliva flowing.
Regular dental visits catch cavities in their earliest stages, when treatment is simpler and less expensive. A small filling now prevents a root canal later.