A cavity changes appearance as it progresses, starting as a subtle white spot on the enamel and eventually becoming a visible hole with dark discoloration. In its earliest stage, you might not notice anything at all. By the time most people spot a cavity on their own, it has already moved past the surface layer of the tooth. About 21% of adults between 20 and 64 have at least one untreated cavity right now, so knowing what to look for at each stage can help you catch decay before it becomes painful or expensive to fix.
The Earliest Stage: White Spots
Before a cavity becomes a hole, it starts as a flat, chalky white patch on the tooth surface. This happens when acids from bacteria dissolve minerals out of the enamel, making it more porous. The damaged enamel loses its natural shine and looks opaque compared to the healthy tooth around it. At this point, there is no physical hole, no pain, and no sensitivity. Most people walk right past this stage without realizing anything is wrong.
These white spot lesions can be tricky to see. They often only become visible after the tooth surface has been dried, which is one reason your dentist uses that little air sprayer during exams. When the tooth is wet with saliva, early demineralization can look completely normal. The good news is that at this stage, the process is still reversible. Fluoride treatments and improved oral hygiene can help the enamel remineralize and heal itself before a true cavity forms.
Color Changes as Decay Deepens
Once decay moves beyond the initial white spot, the color shifts. You may notice a yellowish or light brown discoloration, particularly in the grooves on the chewing surfaces of your back teeth. This means the enamel is breaking down more significantly but may not yet have formed an obvious hole. In the pits and fissures of molars, this often looks like a brown line tracing the natural grooves of the tooth, which people sometimes mistake for a stain.
As the decay works through the enamel and reaches the softer dentin layer underneath, the color darkens further. You might see a grayish shadow visible through the remaining enamel, even if the surface still looks mostly intact. This shadowing is a sign that the cavity is deeper than it appears. By the time a spot turns dark brown or black, the decay is well established and almost certainly needs professional treatment.
What a Full Cavity Looks Like
A fully developed cavity is a visible hole or pit in the tooth. It can be tiny, just a small dark dot in a molar groove, or it can be large enough to feel with your tongue. The edges of the hole often look darker than the surrounding tooth, ranging from brown to black. The surface around the opening may feel rough or slightly soft if you run your tongue over it. In some cases, you can see the lighter, yellowish dentin exposed inside the hole where enamel has broken away.
On the chewing surfaces of molars, cavities tend to form in the deep grooves and pits where food and bacteria collect. On the smooth sides of teeth, they often appear near the gum line or at contact points between teeth. Front teeth can develop cavities too, typically showing up as brown or black spots along the edges or near the gums.
Cavities Between Teeth
Some of the hardest cavities to spot are the ones that form between teeth, in the tight spaces where your toothbrush can’t reach. These interproximal cavities are usually invisible to you in the mirror until they’ve grown quite large. When they do become visible, they typically appear as a dark area or shadow between two teeth, sometimes making the edge of one tooth look grayish or translucent in an unusual way. This is one of the main reasons dentists take regular X-rays, since these cavities are often caught on film long before you’d ever see them yourself.
If you notice floss catching or shredding in a particular spot, or a persistent dark shadow between teeth, those are worth mentioning at your next dental visit.
How to Tell a Cavity From a Stain
Not every dark spot on a tooth is a cavity, and telling the difference can be confusing. A few visual cues help. Stains from coffee, tea, or tobacco tend to affect broad areas of the tooth or even multiple teeth at once. A cavity, on the other hand, typically shows up as a single dark spot, often black, brown, or gray, concentrated in one location. Stains also don’t create holes or soft spots. If you can see or feel an actual pit or opening in the tooth surface, that’s a cavity, not a stain.
Texture matters too. A stained tooth still feels smooth and hard. A decaying tooth may feel sticky, rough, or slightly soft in the affected area. Location is another clue: dark spots sitting right in the grooves of a molar or along the gum line are more suspicious for decay than general discoloration spread across the front of a tooth.
What Cavities Look Like in Children
Cavities in baby teeth have a distinctive pattern. They often appear first on the upper front teeth, right along the gum line. The earliest sign is a dull white band of demineralized enamel running across the tooth near the gums. This can progress quickly in young children, turning into yellow or brown soft areas that may affect several front teeth at the same time. Because baby tooth enamel is thinner than adult enamel, decay can spread faster and look more dramatic in a shorter period.
This pattern is sometimes called “baby bottle decay” because it’s associated with prolonged exposure to milk or juice, but the formal term is early childhood caries. Nearly 18% of children aged 6 to 8 have untreated decay in their baby teeth. If you notice chalky white patches or brownish soft spots near the gum line of your child’s front teeth, those are worth getting checked promptly.
Signs a Cavity Has Reached Advanced Stages
When a cavity goes untreated long enough, the decay can reach the nerve inside the tooth and eventually cause an infection. At this point, the visual signs extend beyond the tooth itself. You might notice a large, dark hole with crumbling edges, or a tooth that has broken down so much that a significant portion of its structure is gone. The tooth may look gray or blackish overall rather than just in one spot.
If infection develops, the gums near the affected tooth can swell. A dental abscess looks like a small boil or pimple on the gum tissue, usually darker than the surrounding gum and visibly swollen. The swelling can range from a small bump to a noticeably puffy area. At this stage, you’ll almost certainly have pain, sensitivity to hot and cold, or a persistent bad taste in your mouth alongside the visible signs.