A cavity changes appearance as it progresses, starting as a subtle white spot on the tooth surface and eventually becoming a visible hole with brown or black discoloration. In its earliest stage, you might not notice anything at all. By the time most people spot a cavity on their own, the decay has already moved past the outer enamel and into the softer layer beneath it.
The Earliest Stage: White Spots
Before a cavity becomes a hole, it starts as a flat, chalky white patch on the tooth. This happens when acids from bacteria dissolve minerals out of the enamel, creating tiny pores in the surface. Light scatters differently through these porous areas, making them look opaque and dull compared to the healthy enamel around them. The spot loses its natural shine and appears matte or frosty.
These white spots are easy to miss. They’re most visible when the tooth surface is dry, which is why your dentist may blow air on your teeth during an exam. An active white spot lesion tends to appear whitish or yellowish, feels rough if you run your tongue over it, and usually sits near the gum line where plaque collects. At this point, the surface is still intact. There’s no hole, no pain, and no sensitivity, because enamel has no nerves.
This stage is actually reversible. Fluoride treatments, better brushing habits, and saliva’s natural repair process can push minerals back into the weakened enamel and stop the cavity from forming. A dentist won’t place a filling for a white spot lesion unless it keeps getting worse.
Brown and Dark Spots
If remineralization doesn’t happen, the white spot darkens. You may see light brown, dark brown, or black discoloration on the tooth surface. This color change happens as the porous enamel picks up staining from food, drinks, and bacteria. A dark spot doesn’t always mean the cavity is actively getting worse. Sometimes a lesion arrests on its own and turns darker but becomes hard and shiny to the touch. An active lesion, by contrast, stays rough and soft.
At this stage, the surface may still look mostly smooth from a distance. You won’t necessarily feel pain yet, since the decay hasn’t reached the inner layer of the tooth where nerves live. Many people mistake these spots for normal staining from coffee or tea.
Visible Holes and Pits
Once the enamel breaks down completely, you get what most people picture when they think of a cavity: an actual hole in the tooth. It may look like a small pit, a dark crater, or a rough, jagged opening on the chewing surface. The edges of the hole often appear brown or black. You might feel it with your tongue as a sharp edge, a rough divot, or a spot where food constantly gets stuck.
At this point, bacteria have reached the dentin, the softer tissue underneath the enamel. Dentin is yellowish, which is why the inside of a cavity often looks tan or dark yellow before turning brown or black. Because dentin contains microscopic tubes that connect to the tooth’s nerve, this is typically when sensitivity starts. Hot, cold, or sweet foods may trigger a sharp sting. The visual size of the cavity on the surface doesn’t always match how much damage exists underneath. Decay can spread wider through the softer dentin while the enamel opening stays relatively small.
Cavities You Can’t See
Some cavities form in places where you’ll never spot them in a mirror. The most common hidden location is between teeth, where two teeth press together. These interproximal cavities develop in a zone you can’t see or reach easily. By the time a dark spot or hole becomes visible from the outside, the decay is usually well advanced. Subtle clues include dental floss that shreds or snags in a spot where it didn’t before, or a tooth that suddenly feels sensitive when you bite down.
Cavities can also form underneath existing fillings. Over time, chewing pressure and grinding can crack or chip a filling, breaking the seal between the restoration and the tooth. Bacteria slip into the gap and cause new decay that’s completely hidden from view. Your dentist detects these with X-rays or by probing around the filling’s edges with a thin instrument.
On X-rays, cavities show up as dark shadows on the tooth. Healthy enamel and dentin block X-rays and appear bright white, so any area where mineral has been lost lets the X-rays pass through and creates a telltale dark spot on the image. This is how dentists catch decay that hasn’t produced any visible signs or symptoms yet. Not all cavities cause pain, especially in the early and middle stages, so a cavity-free appearance in the mirror doesn’t guarantee a cavity-free mouth.
How Cavities Look in Baby Teeth
Cavities in children’s baby teeth tend to look similar to those in adult teeth, but they progress faster and can appear more dramatic. Baby teeth have a thinner layer of enamel, which means bacteria break through to the dentin more quickly. A small white spot can become a visible brown hole in less time than it would in a permanent tooth. Cavities in baby teeth also tend to appear broader and shallower on the front teeth, sometimes showing up as a wide band of brown or yellow discoloration along the gum line, particularly in toddlers who fall asleep with a bottle.
What Pain Tells You About Size
A cavity’s appearance and the pain it causes don’t always line up the way you’d expect. A large discolored area might cause no discomfort at all if it hasn’t reached the nerve, while a tiny-looking spot could produce intense sensitivity if it’s in a thin area of enamel directly over the pulp. Once decay reaches the innermost part of the tooth where the nerve and blood supply live, pain often becomes persistent and can throb on its own without any trigger. At that point, the tooth may need more than a simple filling, potentially requiring a crown or root canal treatment depending on how much structure remains.
The practical takeaway: if you see a white chalky patch, a dark spot, or an actual hole on any tooth, the decay is already underway. White spots caught early can still be reversed without drilling. Anything beyond that typically needs a filling to stop the damage from spreading deeper.