A black discoloration on the back of your tongue is almost always caused by one of two things: a harmless condition called black hairy tongue, where tiny bumps on the tongue’s surface grow abnormally long and trap pigment, or a temporary chemical reaction from taking a bismuth-containing medication like Pepto-Bismol. Both look alarming but are rarely a sign of anything serious.
What Black Hairy Tongue Actually Is
Your tongue is covered in small, finger-like projections called filiform papillae. Normally they’re about 1 mm long, and your body sheds their outer layer of dead skin cells regularly, the same way skin elsewhere on your body turns over. Black hairy tongue happens when that shedding process stalls. The papillae keep growing without being worn down, sometimes reaching more than 15 mm in length. At that size, they create a fuzzy, hair-like texture that traps bacteria, food particles, and pigments from what you eat and drink.
The color itself comes from those trapped substances. Coffee, tea, red wine, and tobacco are common culprits. The overgrown papillae can appear brown, green, yellow, or white depending on the source of the staining, but dark brown to black is the most common shade, which is why the condition gets its name.
The Most Common Causes
Poor oral hygiene and a soft-food diet are the two most common triggers. When you eat mostly soft foods, there’s very little friction against the tongue’s surface to naturally scrub away dead cells. Without that mechanical wear, the papillae accumulate instead of shedding.
Several other habits and exposures are strongly linked to the condition:
- Heavy coffee or tea drinking stains the elongated papillae and makes the discoloration more visible.
- Tobacco use irritates the tongue surface and contributes to buildup.
- Heavy alcohol consumption disrupts the normal cell turnover process.
- Peroxide-based mouthwashes and gargling with hydrogen peroxide can trigger or worsen the condition. Any mouthwash containing an oxidizing agent carries this risk.
- Antibiotics can alter the balance of bacteria in your mouth, allowing pigment-producing organisms to flourish on the tongue’s surface.
Men, older adults, people who smoke, and anyone who has had the condition before are at higher risk.
Pepto-Bismol and Other Bismuth Products
If the blackening appeared suddenly after taking an over-the-counter stomach medication, bismuth is likely the explanation. When bismuth (the active ingredient in Pepto-Bismol and similar products) meets trace amounts of sulfur in your saliva, it forms a compound called bismuth sulfide, which is jet black. Since many everyday foods contain sulfur compounds, this reaction happens easily.
This type of blackening is purely cosmetic and temporary. It typically fades on its own within a few days after you stop taking the medication. Unlike true black hairy tongue, it doesn’t involve any change in the texture or length of your papillae.
How to Get Rid of It
Black hairy tongue usually clears up once you address the underlying cause. The core fix is simple: gently brush your tongue every time you brush your teeth, using either a soft-bristled toothbrush or a flexible tongue scraper. This provides the mechanical friction your tongue needs to shed those overgrown papillae normally.
Beyond brushing, focus on removing whatever triggered the buildup in the first place. Cut back on coffee, tea, or alcohol if you’re a heavy consumer. Stop using tobacco. Switch to a mouthwash that doesn’t contain peroxide or other oxidizing agents. If your diet is mostly soft foods, adding crunchier, more textured foods gives your tongue a natural scrubbing surface throughout the day.
Most people see noticeable improvement within a few weeks of consistent tongue cleaning and removing the trigger. The papillae gradually return to their normal length as the tongue’s natural shedding cycle resumes.
When the Color Could Signal Something Else
In the vast majority of cases, a black tongue is benign. But certain signs should prompt a closer look. Any sore or discolored patch on the tongue that doesn’t heal or at least improve within two weeks deserves medical attention. The same goes for unexplained bleeding from a spot on the tongue, numbness or loss of sensation, pain that persists, or swelling in the jaw, tongue, or lymph nodes in the neck.
These symptoms don’t automatically mean cancer, but oral cancers can sometimes show up as unusual color or texture changes in the mouth. Red patches, white patches, or a mix of the two on the tongue or inner cheeks are the patterns most associated with precancerous changes. A persistent black patch that doesn’t respond to improved hygiene and doesn’t match the typical fuzzy texture of hairy tongue is worth having evaluated by a dentist or an ear, nose, and throat specialist.