If you’re staring at a dark spot on your tooth or wincing at a sudden zing of pain, the short answer is: a cavity looks like a small hole or persistent dark spot that doesn’t go away with brushing, and it often comes with sensitivity or pain that lingers. But telling the difference between a cavity, a stain, and normal sensitivity isn’t always obvious. Here’s how to read the signs your tooth is giving you.
What a Cavity Actually Looks Like
Cavities don’t always start as visible holes. The earliest sign of tooth decay is a white spot on the enamel that looks chalky, matte, and opaque. This is the tooth losing minerals from acid exposure, and at this stage, the surface is still intact. No hole has formed yet.
If that white spot progresses, it darkens to brown, then eventually grey or black as the enamel breaks down and a small hole opens up. Once a hole forms, you’re looking at an actual cavity. A more advanced cavity has a visible dark center of damaged tooth surrounded by a pearly, opalescent white halo where the deeper layers of enamel have started to weaken from the inside out. The surface over that halo can still look shiny, which is why some cavities are surprisingly hard to spot in a mirror.
Cavities between teeth are even sneakier. You can’t see them, but you might notice that dental floss catches or shreds in a particular spot, or that food constantly gets stuck between the same two teeth. Those are tactile clues that the smooth surface between teeth has broken down.
How to Tell a Cavity From a Stain
Surface stains and cavities can both show up as brown or dark spots, so color alone won’t give you the answer. The key differences come down to texture, permanence, and whether you feel anything.
- Stains are surface discoloration. They can appear yellow, brown, grey, or even green, and they tend to change size depending on what you eat, drink, or how well you brush. A good cleaning, whether at home or at the dentist, can reduce or remove them.
- Cavities are structural damage. The spots are brown, grey, or black, and no amount of brushing makes them go away. They only get bigger over time. If you run your tongue over the area and feel a rough edge or a small pit, that’s a strong signal it’s a cavity rather than a stain.
Sensitivity is another dividing line. Stains don’t hurt. If the dark spot comes with a zing when you drink something cold or a dull ache when you chew, decay is the more likely explanation.
Sensitivity vs. Cavity Pain
Tooth sensitivity and cavity pain feel different in ways that matter. Sensitivity from things like exposed root surfaces or worn enamel is typically sharp, brief, and tied to a specific trigger: a sip of ice water, a bite of something sweet, a blast of cold air. The discomfort fades within seconds once the trigger is gone.
Cavity pain behaves differently. It tends to linger after the trigger disappears, or it shows up as a dull ache with no obvious trigger at all. Pain when you bite down or chew is a particularly telling sign, because it suggests the tooth’s structure has weakened enough that normal pressure causes discomfort. If you notice pain that sticks around, gets gradually worse over weeks, or wakes you up at night, that points toward decay that has reached deeper layers of the tooth.
How Decay Progresses Layer by Layer
A tooth has three main layers, and the symptoms you feel depend on how deep the decay has gone.
In the enamel stage, you typically feel nothing. Enamel has no nerves, so early cavities are painless. This is why small cavities often get caught at dental checkups before you ever notice them yourself. You might see a white or brown spot, but that’s it.
Once decay pushes through to the dentin, the softer layer beneath the enamel, things speed up. Dentin is less resistant to acid, so the cavity grows faster. It also contains tiny tubes that connect to the tooth’s nerve, which is why this stage brings noticeable sensitivity to hot, cold, and sweet foods. This is usually the point where people start wondering “is it a cavity?”
If decay reaches the pulp, the innermost tissue containing the nerve and blood supply, the tooth can become seriously painful. The pulp swells in response to the infection, but it’s trapped inside a hard shell of tooth with nowhere to expand. That pressure on the nerve causes intense, throbbing pain. Left untreated, bacteria can push past the root tip and form an abscess, a pocket of infection that causes severe pain radiating into the jaw.
When It Can Still Be Reversed
Not every sign of decay means you need a filling. The white spot stage, where minerals are leaving the enamel but no hole has formed, is actually reversible. Fluoride treatments, dental sealants, or even consistent use of fluoride toothpaste can help the enamel remineralize and repair itself. At this stage, there’s no need for drilling or any permanent intervention.
Once the surface breaks and an actual hole forms, that line has been crossed. Lost tooth structure doesn’t grow back, and the cavity will only get larger as bacteria settle into the space. A filling or other restoration becomes necessary to stop the process and protect what’s left of the tooth. The earlier this happens, the smaller and simpler the repair.
What You Can Check at Home
You can gather useful clues before your dental visit, even though only an X-ray or clinical exam can confirm a cavity for certain. Here’s what to look for:
- Visual changes: A persistent white, brown, or dark spot that doesn’t respond to brushing. Check in good light with a dry tooth surface, since saliva can mask the chalky appearance of early decay.
- Texture: Run your tongue over the area. A rough spot, a sharp edge, or a small pit suggests enamel has broken down.
- Floss test: If floss consistently shreds or catches between the same two teeth, the surface there may be damaged.
- Pain pattern: Lingering pain after eating or drinking, a dull ache without a trigger, or pain when biting down all point toward active decay rather than simple sensitivity.
If any of these match what you’re experiencing, it’s worth getting it looked at sooner rather than later. The difference between a reversible white spot and a cavity that needs a filling can be a matter of months.