Tooth stains fall into two broad categories: those that build up on the surface and those that form inside the tooth itself. Surface stains come from pigmented foods, drinks, tobacco, and bacteria that cling to the thin film coating your enamel. Internal stains develop when something changes the structure or color of the tooth from within, whether that’s an injury, a medication, or simply aging. Understanding which type you’re dealing with helps explain why some stains respond to whitening toothpaste while others don’t budge.
Surface Stains From Food, Drink, and Tobacco
The color compounds in deeply pigmented foods and drinks, called chromogens, are the most common cause of surface staining. Coffee, tea, red wine, and blueberries are frequent offenders. These chromogens don’t bond directly to smooth, clean enamel. Instead, they latch onto the sticky biofilm (plaque) and the thin protein layer that naturally coats your teeth throughout the day. The rougher or more built-up that layer is, the more pigment it absorbs.
Tannins, found in tea, red wine, and some fruits, make staining worse by helping chromogens stick more aggressively. Acidic foods and drinks compound the problem by softening and roughening the enamel surface, giving pigments more texture to grip. This is why a glass of red wine (acidic, tannin-rich, and deeply colored) is a triple threat for staining, while black coffee with its lower acidity stains somewhat less aggressively despite its dark color.
Tobacco causes some of the most stubborn surface stains. Tar compounds from smoking, chewing, or dipping tobacco produce brown discoloration that penetrates deeply into the biofilm layer. Over time, these surface stains can actually work their way into the tooth structure itself, becoming a form of internal stain that’s much harder to reverse.
How Plaque and Tartar Trap Color
Plaque is the soft, sticky film of bacteria that forms on your teeth throughout the day. On its own, it can give teeth a yellowish tint. When plaque isn’t removed regularly, it mineralizes into tartar, a hard deposit that your toothbrush can’t scrape off. Tartar starts out yellowish but acts like a sponge for whatever pigments pass through your mouth. If you drink a lot of coffee, tea, or red wine, or if you smoke, tartar gradually darkens to brown or even black.
This is why people with the same diet can have very different levels of staining. Someone who brushes and flosses thoroughly has less plaque surface area to absorb color. Someone with tartar buildup along the gumline or between teeth will accumulate stains much faster in those spots, even from moderate coffee consumption.
Bacteria That Create Their Own Color
Not all surface stains come from what you eat or drink. Certain bacteria and fungi produce pigments on their own, creating distinctive colored deposits on teeth. Green stains, most common in children, come from chromogenic bacteria and fungi that thrive when oral hygiene is inconsistent, especially on teeth with surface irregularities. Orange stains are caused by different bacterial species and also signal poor oral hygiene. Black staining can come from iron compounds in saliva interacting with specific bacteria.
These bacterial stains look alarming but are entirely on the surface. A professional cleaning removes them, and better brushing habits prevent them from coming back.
Medications and Mouthwashes
Several common oral care products cause brown staining as a side effect. Chlorhexidine mouthwash, often prescribed for gum disease, is one of the most well-known culprits. Certain fluoride rinses and antiseptic mouthwashes containing cetylpyridinium chloride can also leave brown deposits on teeth with regular use. These stains are surface-level and removable, but they can be frustrating if you’re using the product long-term.
Iron-containing liquid supplements are another common source. They leave black or dark brown stains, particularly in children who take liquid iron for anemia. Drinking through a straw and rinsing the mouth afterward helps reduce this effect.
Why Teeth Yellow With Age
Even with perfect hygiene and no coffee habit, teeth gradually turn more yellow over the years. This happens because the outer enamel layer slowly thins with decades of chewing, brushing, and acid exposure. Underneath that enamel sits dentin, a naturally yellowish layer that forms the bulk of the tooth. As enamel wears down, more dentin shows through, and teeth take on a warmer, darker tone. This process is universal and accelerates if you grind your teeth, consume a highly acidic diet, or brush with excessive force.
Years of accumulated surface staining also contribute. Pigments that started on the surface can gradually migrate into the enamel’s microscopic pores, becoming intrinsic stains that whitening toothpaste alone can’t reach.
Tooth Trauma and Dark Discoloration
If a single tooth turns gray, dark brown, or nearly black, a past injury is the most likely cause. When a tooth takes a hard hit, blood vessels inside the pulp (the soft tissue at the tooth’s core) can rupture. The blood leaks into the surrounding hard tissue, and as the red blood cells break down, they release iron-based compounds that seep into the tiny tubes within the dentin. This stains the tooth from the inside out.
The color change doesn’t always happen right away. A tooth can darken weeks or even months after the original injury. It may first appear grayish, then shift to a dark yellow-brown over time. In some cases, the pulp heals and the tooth lightens somewhat on its own. In others, the pulp dies completely, and the discoloration is permanent without treatment. Because the stain is deep inside the tooth, surface whitening products have no effect. A dentist can sometimes lighten trauma-darkened teeth with internal bleaching, or the tooth may need a crown or veneer.
Antibiotics During Childhood
Older tetracycline antibiotics are notorious for causing permanent tooth discoloration when taken by children under eight. These drugs bind to calcium in developing teeth, creating gray-brown or yellow-brown bands that are locked into the tooth structure. The staining pattern depends on which teeth were forming at the time the drug was taken. A warning label was added to all tetracycline-class antibiotics in 1970 advising against their use in young children.
Doxycycline, a newer antibiotic in the same family, binds less readily to calcium. The CDC notes that the best available evidence shows short courses of doxycycline do not cause dental staining in children under eight. This distinction matters because doxycycline is sometimes the only effective treatment for certain serious infections in young children.
Fluorosis: White Spots From Too Much Fluoride
Dental fluorosis happens when a child ingests too much fluoride while their permanent teeth are still developing below the gumline. The result is white flecks, spots, or faint lines on the enamel surface. In more severe cases, the spots can turn brown and the enamel may become pitted. The severity depends on how much fluoride the child consumed and for how long.
The most common sources of excess fluoride are swallowing fluoride toothpaste (young children often swallow rather than spit) and drinking water with fluoride levels above the recommended concentration. The U.S. Public Health Service recommends a water fluoride level of 0.7 mg/L, a number chosen to protect teeth from decay while minimizing fluorosis risk. Once fluorosis marks are present, they’re permanent, though cosmetic treatments can reduce their visibility.
Genetics and Natural Tooth Color
Some variation in tooth color is simply inherited. The natural thickness and translucency of your enamel, the shade of your dentin, and even how your enamel mineralizes during development all have genetic components. Two people with identical diets and hygiene habits can have noticeably different baseline tooth color. This is why some people’s teeth never look particularly white even when they’re perfectly healthy, and why whitening results vary so much from person to person.
Certain conditions that affect enamel formation, such as enamel hypoplasia (underdeveloped enamel) or hypocalcification from high fevers during childhood, can also produce white or brown spots on teeth. These aren’t stains in the traditional sense but structural differences in the enamel that change how light reflects off the tooth surface.