Unhealthy teeth can look surprisingly different depending on what’s going on. Some problems announce themselves with obvious dark spots or swelling, while others start as subtle changes you’d easily miss. Nearly 21% of adults between 20 and 64 have at least one tooth with untreated decay, so knowing what to look for can help you catch problems before they get worse. Here’s a visual guide to the most common signs.
White Spots: The Earliest Warning
The very first sign of tooth decay isn’t a dark spot. It’s a chalky white one. These white spot lesions appear when minerals like calcium and phosphate start leaching out of the enamel surface, creating tiny pores that scatter light differently than healthy enamel. The result is a small, milky patch that looks more opaque than the surrounding tooth.
You’ll typically find these spots along the gum line or between teeth, where plaque tends to sit undisturbed. An active white spot lesion has a dull, rough surface rather than a smooth, shiny one. At this stage, the damage hasn’t broken through the enamel yet, so the tooth can still recover with better cleaning habits and fluoride exposure. Once you ignore it long enough, that white patch will darken to brown, signaling that the enamel is breaking down further.
Not every white spot means decay, though. Fluorosis (from too much fluoride during childhood) and developmental enamel defects can create similar-looking marks. Fluorosis spots tend to affect multiple teeth in a symmetrical pattern, while decay-related white spots usually show up in isolated areas where plaque collects.
Brown and Black Spots: Cavities in Progress
As decay advances past the white spot stage, the affected area darkens. A brownish discoloration on a tooth surface often means the enamel has started to break down, and the underlying layer (dentin) may be exposed. Dentin is naturally softer and more yellow than enamel, so once a cavity reaches it, the process accelerates.
A fully developed cavity can appear as a visible hole or pit in the tooth, ranging from light brown to completely black. Black discoloration usually indicates that decay has been present for a long time and has reached deeper structures. You might also notice that the tooth feels sharp or rough when you run your tongue over it, or that food gets stuck in the same spot repeatedly. Pain at this stage isn’t guaranteed. Some cavities grow silently for months before they start causing sensitivity to hot, cold, or sweet foods.
Yellow, Transparent, or Worn-Down Teeth
Enamel erosion looks different from cavities. Instead of dark spots, you’ll notice teeth that appear increasingly yellow over time. This happens because as the outer enamel layer thins, the yellowish dentin underneath shows through more prominently. The biting edges of front teeth may become slightly transparent or translucent, almost glassy-looking.
Other signs of eroded enamel include small pits or dents on the chewing surfaces, chipped edges, and teeth that look shorter or more rounded than they used to. The edges of teeth may feel rough, jagged, or uneven. Erosion is commonly caused by acidic foods and drinks, acid reflux, or frequent vomiting, and it affects the tooth surfaces broadly rather than creating isolated holes like cavities do. Once enamel is gone, it doesn’t grow back, and the exposed dentin underneath is far more vulnerable to further damage.
Tartar Buildup Along the Gum Line
Plaque that isn’t removed within a day or two hardens into tartar (also called calculus), a crusty deposit that can’t be brushed or flossed away. Above the gum line, tartar typically appears as a white to light brown, clay-like buildup, most commonly on the inside surfaces of the lower front teeth and the outer surfaces of the upper back molars. These locations correspond to where saliva glands release the most mineral-rich fluid, which accelerates the hardening process.
Tartar that forms below the gum line is a different story. It picks up pigments from blood and anaerobic bacteria, giving it a characteristic dark brown or black color. You won’t always see subgingival tartar directly, but you might notice dark discoloration peeking out at the gum line. Heavy tartar buildup is a strong visual indicator of long-standing poor oral hygiene, and it creates a rough surface that traps even more bacteria against the teeth and gums.
Red, Swollen, or Receding Gums
Unhealthy teeth rarely exist without unhealthy gums. Healthy gum tissue is firm, pale pink, and fits snugly around each tooth. Gingivitis, the earliest stage of gum disease, turns gums noticeably redder and puffy-looking. The tissue may appear swollen, and you’ll often see blood on your toothbrush or floss. At this stage, the damage is still reversible.
Left untreated, gingivitis progresses to periodontitis, which causes the gums to pull away from the teeth. This gum recession exposes parts of the tooth root that are normally hidden, making teeth look unusually long. You might notice that the spaces between teeth near the gum line seem larger than they used to, or that a yellowish root surface is visible where pink gum used to be. Dentists measure the pockets between gums and teeth to assess severity: healthy pockets are 1 to 3 millimeters deep, while pockets of 5 millimeters or more indicate periodontal disease. Increased sensitivity to temperature and sweets is a common side effect of root exposure.
Pimple-Like Bumps on the Gums
A dental abscess, one of the more alarming signs of unhealthy teeth, creates a visible bump on the gum that looks like a pimple or boil. It’s typically darker than the surrounding gum tissue and swollen, sometimes mildly, sometimes severely. This bump is a pocket of infection, and it may come and go or drain a foul-tasting fluid into your mouth.
An abscessed tooth itself may appear darker than neighboring teeth. When the nerve inside a tooth dies from infection or trauma, the tooth can gradually turn gray, dark yellow, or brown. This discoloration comes from the breakdown of tissue inside the tooth and is often one of the first things people notice before they feel any pain.
Cracks and Fracture Lines
Cracked teeth range from harmless surface lines to serious structural fractures. Shallow craze lines, the tiny vertical cracks visible on many adult teeth, are limited to the outer enamel and are mostly cosmetic. They’re extremely common and don’t usually indicate a problem.
A more significant crack may show up as a light brown vertical line running through the tooth, sometimes visible only in certain lighting. The gum around a cracked tooth may look swollen at the fracture site. Pain when biting down, especially when releasing the bite, is a hallmark symptom, but the crack itself can be difficult to see without magnification. Teeth with large fillings, teeth that have undergone root canal treatment, and teeth subjected to habitual grinding are most prone to fractures.
Changes on the Tongue
Your tongue offers clues about oral health too. A yellow or orange coating on the tongue’s surface usually signals bacterial overgrowth from poor oral hygiene. A healthy tongue is pink with small, evenly distributed bumps. When cleaning habits slip, bacteria and dead cells accumulate on the tongue’s textured surface, creating a visible discolored film. Regular tongue brushing or scraping typically resolves this, but a persistent coating that doesn’t respond to better hygiene is worth getting checked.