Cavities are permanent holes in your teeth caused by decay. They’re one of the most common health problems in the world: nearly half of U.S. children ages 2 to 19 have had at least one cavity, and roughly 1 in 4 adults between 20 and 64 has untreated decay right now. Understanding how cavities form, what they look and feel like, and how they’re treated can help you catch them early, when they’re easiest to fix.
How Cavities Form
Your mouth is home to hundreds of species of bacteria, and some of them thrive on sugar. When you eat or drink something containing fermentable carbohydrates (sugar, starch, fruit juice), bacteria in the sticky film on your teeth, called plaque, consume those sugars and produce acid as a byproduct. One species, Streptococcus mutans, is especially effective at this. It also produces a glue-like substance that helps it stick to tooth surfaces and build up thicker layers of plaque.
That acid pulls calcium and phosphate out of your tooth enamel in a process called demineralization. Saliva normally counteracts this by buffering the acid and supplying minerals that patch the enamel back up. After each meal or snack, the acid level in plaque spikes and then returns to normal within a few minutes, thanks to saliva’s buffering agents. But when acid attacks happen too often, or saliva can’t keep up, the enamel breaks down faster than it can repair itself. Over time, that imbalance creates a cavity.
Stages of Tooth Decay
Cavities don’t appear overnight. They progress through distinct stages, and the earlier you catch them, the simpler and less painful the fix.
Demineralization
The first sign is a small, white, chalky spot on the enamel where minerals have started to leach out. At this point there’s no actual hole yet, and the process can still be reversed with fluoride treatments, better brushing, or dietary changes. You won’t feel any pain or sensitivity during this stage.
Enamel Decay
If demineralization continues, the enamel surface breaks down and a true cavity, a physical hole, forms. The white spot may turn light brown. Enamel has no nerve endings, so you still might not feel anything, which is why many people don’t realize they have a cavity until a dentist finds it.
Dentin Decay
Beneath the enamel lies dentin, a softer, more porous layer. Once decay reaches dentin, it spreads faster because the tissue is less resistant to acid. Spots on the tooth may darken to a deeper brown. This is often when sensitivity kicks in, particularly to hot, cold, or sweet foods and drinks.
Pulp Damage
The innermost part of a tooth, the pulp, contains nerves and blood vessels. When bacteria reach the pulp, you’ll likely feel genuine pain, not just sensitivity. The discoloration on your tooth may turn very dark brown or black. Treatment at this point typically requires a root canal to remove the infected tissue and save the tooth.
Abscess
Left untreated further, bacteria in the pulp can trigger an infection that produces a pocket of pus at the base of the tooth root. An abscess causes severe, throbbing pain that can radiate into your jaw or face. Swelling of the gums, face, or jaw is common, and some people develop a fever or swollen lymph nodes in the neck. This is a serious infection that needs prompt treatment.
What a Cavity Looks and Feels Like
In the earliest stages, cavities are nearly invisible. The first visual clue is that small white or chalky patch on the tooth surface. As the cavity deepens, the color shifts from light brown to dark brown to black. One practical tip: stains from coffee or tea tend to affect several teeth at once and appear relatively uniform. A single dark spot on one tooth is more likely a cavity than a stain.
Sensation follows a predictable pattern tied to depth. A shallow cavity confined to the enamel feels like nothing at all. Once it hits the dentin, you may notice a twinge when you sip something cold or bite into something sweet. By the time the pulp is involved, the pain can be persistent and sharp. If an abscess forms, the pain often spreads well beyond the tooth itself.
What Raises Your Risk
Cavities come down to the balance between acid attacks and your mouth’s ability to repair itself. Several factors tip that balance toward decay.
Frequent snacking and sipping sugary drinks are the biggest behavioral drivers. Each time you eat something with sugar or starch, your plaque pH drops and stays acidic for several minutes. If you graze throughout the day, your teeth spend more total time under acid attack, giving saliva less opportunity to neutralize and remineralize.
Saliva plays a surprisingly large protective role. It lubricates the mouth, washes away food particles, delivers calcium and phosphate back to the enamel, and contains antibacterial agents that keep harmful bacteria in check. Anything that reduces saliva flow increases cavity risk. Common culprits include certain medications (antihistamines, antidepressants, blood pressure drugs), mouth breathing, dehydration, and some medical conditions that affect the salivary glands.
Other risk factors include poor brushing and flossing habits, lack of fluoride exposure, receding gums that expose tooth roots (which have no protective enamel), and deep grooves on the chewing surfaces of molars where bacteria can hide. Children and older adults tend to be especially vulnerable, though cavities can develop at any age.
How Dentists Find Cavities
You can’t always see or feel a cavity on your own, which is why routine dental exams matter. Dentists use a combination of visual inspection and tools to catch decay early. During a visual exam, they look for discoloration, soft spots, and surface irregularities. A thin metal instrument called an explorer can detect areas where enamel has broken down.
X-rays are especially important for finding cavities between teeth, where they’re impossible to see with the naked eye. A type of X-ray called a bitewing is specifically designed to show decay between teeth and below the gumline. Periapical X-rays provide a view of the entire tooth from crown to root tip, which helps detect deeper infections, bone loss, or cavities near the root.
Treatment Options by Severity
What happens after a cavity is found depends entirely on how far the decay has progressed.
At the demineralization stage, treatment is non-invasive. Fluoride varnishes or prescription-strength fluoride toothpaste can help enamel reabsorb minerals and harden again. No drilling is needed.
Once a true hole has formed in the enamel or dentin, a filling is the standard treatment. The dentist removes the decayed portion and fills the space with a restorative material. The most common options today are composite resin (tooth-colored) and amalgam (silver-colored). Composite fillings are popular because they match your natural tooth color, and their durability has improved significantly. Studies show posterior composite fillings have about a 90% success rate after 10 years, with some lasting well over 20 years. Amalgam fillings have historically been very durable, with survival rates around 94.5% at 7 years, though their use has declined as tooth-colored options have improved.
When decay reaches the pulp, a root canal removes the infected tissue inside the tooth. The tooth is then sealed and usually capped with a crown for protection. If the tooth is too damaged to save, or if an abscess has caused extensive bone loss, extraction may be necessary. The extracted tooth can then be replaced with an implant or bridge.
Preventing New Cavities
Prevention centers on disrupting the cycle of acid production and giving your teeth the materials they need to repair themselves. Brushing twice a day with fluoride toothpaste removes plaque before it can produce significant acid. Flossing cleans the tight spaces between teeth where cavities frequently start and where toothbrush bristles can’t reach.
Reducing how often you expose your teeth to sugar matters more than reducing the total amount. Sipping a soda over two hours causes far more acid damage than drinking the same soda in five minutes, because each sip resets the acid clock. Drinking water between meals helps rinse away food particles and supports saliva production.
For people at higher risk, dentists may recommend dental sealants, which are thin coatings painted onto the chewing surfaces of back teeth to block bacteria from settling into the grooves. Sealants are most commonly applied to children’s permanent molars shortly after they come in, but adults with deep grooves can benefit as well. Prescription fluoride rinses or gels offer additional protection for those with dry mouth or a history of frequent cavities.