Cavities don’t always hurt, especially in the early stages. The first visible sign is usually a chalky white spot on the tooth surface, caused by mineral loss in the enamel. As decay progresses, you may notice brown or dark spots, sensitivity to certain foods and drinks, or eventually a visible hole. Here’s how to recognize what’s happening at each stage.
The Earliest Sign: White Spots
Before a cavity becomes a hole, it starts as a patch of weakened enamel. This shows up as a white, opaque spot on the tooth that looks different from the surrounding enamel. The spot appears because mineral loss changes how light passes through the tooth surface. These white spots are easier to see when your teeth are dry, so you might notice them after sleeping with your mouth open or after blowing air across your teeth.
At this stage, the damage is actually reversible. Fluoride toothpaste, good brushing habits, and reducing sugar intake can help the enamel absorb minerals back and repair itself. But once the decay eats through the enamel and the deeper layer of the tooth (called dentin) collapses, remineralization is no longer possible and a filling becomes necessary.
What a Cavity Feels Like
Sensitivity is one of the most common signs of an active cavity. You might feel a sharp zing or lingering ache when eating or drinking something cold, hot, or sweet. This happens because decay exposes the softer inner layer of the tooth, which contains tiny channels leading toward the nerve. Sugar, temperature changes, and acidic foods can all trigger discomfort through those exposed channels.
Pay attention to how long the sensitivity lasts. A brief flash of discomfort when you bite into ice cream is common even without a cavity. But if the pain lingers for several seconds after the trigger is gone, or if it keeps coming back in the same spot, that’s more suspicious. Sharp, spontaneous pain that hits without any trigger at all can mean the decay has reached the nerve inside the tooth.
What a Cavity Looks Like
As decay progresses beyond the white spot stage, you may see light brown, dark brown, or black discoloration on the tooth. This can appear on the chewing surface, along the gum line, or between teeth. Not every dark spot is a cavity (some staining comes from coffee, tea, or certain foods), but a dark spot that feels rough or sticky when you run your tongue over it is worth having checked.
In more advanced stages, you might feel or see an actual hole in the tooth. Sometimes you’ll notice it because food keeps getting stuck in the same spot, or your tongue finds a rough edge or pit that wasn’t there before. A cavity on a chewing surface often starts in the grooves and pits where your toothbrush bristles can’t reach.
Signs You Might Not Expect
A persistent bad taste in your mouth or bad breath that doesn’t improve with brushing can point to decay. Bacteria living in a cavity produce sulfur compounds, some of which smell like rotten eggs or worse. Food trapped in a decayed area can also begin to break down, adding to the problem. If you notice a foul taste coming from one specific area of your mouth, that’s a clue.
Floss can also tell you something. If your floss shreds or catches in the same spot every time, it may be snagging on a rough edge created by decay between two teeth. Likewise, if a tooth that never bothered you suddenly becomes sensitive to flossing pressure, it’s worth paying attention.
Cavities You Can’t See or Feel
Some cavities are essentially invisible to you at home. Interproximal cavities, the ones that form between teeth, are among the sneakiest. The contact point between two teeth hides the decay from view, and you may not feel any symptoms until the cavity is fairly large. These are best detected with bite-wing X-rays, the kind where you bite down on a small tab while the dentist takes a side image of your back teeth.
Cavities can also form beneath old fillings or crowns, where you can’t see them at all. And decay on the roots of teeth, which becomes more common as gums recede with age, can be hard to spot because root surfaces are naturally darker. This is a big part of why cavities are sometimes discovered at routine dental visits in people who had no symptoms whatsoever.
How Dentists Detect Decay
Your dentist has tools that go well beyond what you can do with a mirror at home. Visual examination catches surface-level changes, but X-rays reveal decay hidden between teeth or beneath existing dental work. Some offices also use laser fluorescence devices, which shine a light on the tooth and measure how much fluorescence bounces back. Decayed tooth structure fluoresces differently than healthy enamel, allowing these tools to catch early decay that isn’t visible yet. Studies comparing these devices to micro-CT scans (the gold standard) show they’re highly accurate at distinguishing healthy enamel from early decay.
Dentists also use a standardized scoring system that classifies decay on a scale from zero (no evidence of caries) through increasingly severe stages: initial changes in enamel, localized enamel breakdown, a dark shadow visible from the deeper tooth layer, and finally distinct or extensive cavities where the inner tooth structure is exposed. This system helps them decide whether a spot needs monitoring, preventive treatment, or a filling.
What Happens If You Ignore It
A cavity doesn’t heal on its own once it’s past the white spot stage. Left untreated, bacteria work through the enamel into the dentin, which is softer and decays faster. From there, infection can reach the pulp, the innermost chamber containing the tooth’s nerve and blood supply. When the pulp becomes infected, the nerve dies and the body mounts an immune response that can lead to an abscess: a pocket of pus around the root of the tooth.
This progression can take months or even years in some cases, but it can also accelerate quickly. An abscess can develop within one to two days of the infection reaching the pulp. At that point, you’re looking at a root canal or extraction rather than a simple filling. The earlier decay is caught, the smaller and less expensive the fix.
A Quick Self-Check
You can do a basic check at home with good lighting and a small mirror. Look for white spots, brown or black discoloration, visible holes, and rough or sticky areas. Run your tongue along every tooth surface and note anything that feels different. Think about whether any specific tooth reacts to hot, cold, or sweet foods.
- White or chalky spots: possible early demineralization, potentially reversible
- Brown or dark spots: likely more advanced decay, especially if the surface feels rough
- Visible hole or pit: a definite cavity that needs professional treatment
- Lingering sensitivity: decay may have reached the dentin or deeper
- Spontaneous pain: the nerve may be involved
- Bad taste from one area: bacteria and trapped food in a decayed spot
- Floss catching or shredding: possible decay between teeth
None of these signs on their own is a definitive diagnosis. And the absence of symptoms doesn’t mean you’re cavity-free, since many cavities are painless until they’re advanced. A dental exam with X-rays remains the only reliable way to know for sure what’s going on.