Tooth decay changes appearance as it progresses, starting as a subtle white spot on the enamel and eventually becoming a visible hole with dark brown or black discoloration. Because early decay can be easy to miss or mistake for a simple stain, knowing what each stage looks like helps you catch problems before they turn painful. Untreated dental caries affects roughly 2.5 billion people worldwide, making it one of the most common health conditions on the planet.
The Earliest Sign: White Spots
Decay doesn’t start as a hole. It starts as a chalky white spot or line on the tooth surface, usually along the gumline. These white spot lesions are areas where minerals have been pulled out of the enamel by acid from bacteria. The spots have a matte, opaque look that stands out from the glossy surface of healthy enamel. Some are only visible when the tooth is dried off, while more established spots are noticeable even on a wet tooth.
At this stage, no actual hole has formed. The enamel surface is still intact, which means the process can sometimes be slowed or reversed with fluoride and better oral hygiene. Most people never notice these spots on their own because they blend in with the natural color of the tooth, especially on back teeth.
What a Cavity Looks Like as It Grows
Once the white spot darkens, decay is moving deeper. A brownish discoloration replaces the chalky white, signaling that the enamel is breaking down further. At this point, you might see a small pit or rough patch where the surface has started to collapse. The color can range from light tan to dark brown depending on how long the process has been underway.
When decay pushes through the enamel into the softer tissue underneath (called dentin), things accelerate. Dentin is less resistant to acid, so the cavity can widen quickly beneath a relatively small opening in the enamel. On the chewing surfaces of molars, this sometimes shows up as a dark shadow visible through the grooves of the tooth, even before an obvious hole appears. On the surface, you may see a defined brown, black, or grayish spot that keeps getting larger over time.
Once the outer surface fully collapses, the result is a visible hole or crater in the tooth. It may catch food, feel rough or sticky to your tongue, and appear dark inside. Some cavities are on surfaces you can easily see in a mirror, but many form between teeth where they’re hidden from view.
Decay Between Teeth
Cavities that form between teeth are particularly tricky to spot. In the earliest stage, you might notice a faint white lesion or shadowing on the side of a tooth, but only if you look closely with good lighting. As the decay progresses into the dentin, a dark shadow can become visible through the enamel near the contact point between two teeth. In more advanced cases, the enamel caves in and you can see an actual hole with exposed dentin, sometimes with widespread dark discoloration. Dentists often rely on X-rays to catch these cavities because the visual signs are easy to miss from the outside.
Decay Along the Gumline and on Roots
In adults with receding gums, the root surface of the tooth becomes exposed. Root surfaces don’t have the hard protective enamel that covers the crown, so they’re far more vulnerable to acid attack and decay spreads through them faster. Root decay typically appears as a yellowish or dark brown patch right at or just below the gumline. The texture can feel soft or leathery rather than hard like healthy tooth structure.
This type of decay is most common in older adults and people with gum disease. It can wrap around the base of a tooth, making it structurally weak even if the visible crown still looks fine.
Decay Around Fillings and Crowns
Teeth that already have dental work aren’t immune to new decay. Recurrent decay develops when gaps, cracks, or leakage form around the edges of an existing filling or crown. The telltale signs include brown or black staining at the margins of the restoration, visible chips or cracks in the filling material, or a filling that no longer seems to fit the tooth snugly. Sometimes the tooth itself darkens or grays around the edges of a white filling. This type of decay can be hard to distinguish from normal wear, so it’s often caught during routine dental exams rather than by the patient.
How to Tell Decay From a Stain
Dark spots on teeth aren’t always cavities. Coffee, tea, tobacco, and certain foods leave surface stains that can look similar. A few differences help you tell them apart:
- Texture: A cavity may feel sticky, rough, or soft when you run your tongue over it. A stain sits on a smooth, hard surface.
- Change over time: Stains may shrink, shift, or disappear after brushing or changing your diet. Cavities only get bigger.
- Sensitivity: Decay often causes sensitivity to hot, cold, or sweet foods and drinks. Stains don’t.
- Holes: A visible pit or opening in the tooth points to decay, not staining. Even a tiny hole that traps food is a red flag.
- Location: Stains tend to appear in similar patterns across multiple teeth (like along the gumline from coffee). A single dark spot on one tooth, especially in a groove or between teeth, is more suspicious for decay.
What Advanced Decay and Infection Look Like
When a cavity reaches the innermost part of the tooth, the nerve tissue becomes inflamed and swollen. Because there’s no room inside the tooth for swelling, the pressure builds and produces pain that can radiate to the jaw, ear, or cheek. The tooth itself may appear significantly broken down, with large portions missing or darkened.
If bacteria from the decay cause a full infection, a pocket of pus called an abscess can form at the tip of the root. The most visible sign is a small red bump on the gum near the affected tooth, sometimes called a gum boil. It looks like a pimple and may drain a foul-tasting fluid. In more serious cases, the infection can cause facial swelling, red swollen skin on the cheek, fever, and pain that doesn’t respond to over-the-counter painkillers. Facial swelling from a dental abscess is a medical emergency that needs prompt treatment.
Why Some Decay Is Invisible to You
Not all cavities produce visible signs you can spot in the mirror. Decay between teeth, under existing fillings, or in the early white-spot stage can progress silently. Dentists use tools beyond the naked eye to find these hidden problems. X-rays reveal shadows in the tooth structure where minerals have been lost. Transillumination, where a bright light is shone through the tooth, makes decayed areas appear dark compared to healthy enamel because the damaged tissue blocks light. By the time a cavity is large enough for you to see or feel on your own, it has usually been developing for months or longer.