A black tongue is almost always harmless, even though it looks alarming. The most common explanation is a condition called black hairy tongue, where the tiny bumps on your tongue’s surface grow longer than usual and trap pigments from food, drinks, bacteria, or tobacco. Less commonly, you may have taken something the night before, like an antacid containing bismuth, that chemically stained your tongue while you slept.
What’s Happening on Your Tongue
Your tongue is covered in small, finger-like projections called papillae. Normally, these shed regularly and stay short. But when shedding slows down, the papillae elongate and start trapping everything that passes through your mouth: pigments from coffee, tea, and wine, residue from tobacco, bacteria, yeast, and food particles. As these substances accumulate, the papillae darken and can take on a black, brown, or greenish tint. The elongated papillae also create a “furry” or “hairy” texture that makes the discoloration more noticeable.
This buildup can happen gradually over days or weeks, but you might only notice it suddenly one morning if the staining reaches a visible threshold overnight. The color itself comes from pigment-producing bacteria and chromogens (color compounds in food and drinks) that concentrate on the papillae’s surface.
The Most Likely Causes
If you took Pepto-Bismol or another bismuth-based antacid before bed, that’s probably your answer. The bismuth in the active ingredient reacts with sulfur that occurs naturally in your saliva and digestive tract, forming a black compound called bismuth sulfide. This reaction can coat your tongue (and darken your stool) within hours. It’s completely temporary and fades on its own once the bismuth clears your system.
If you didn’t take any antacids, the cause is more likely a combination of everyday habits:
- Coffee, black tea, or red wine: These contain tannins and other color compounds that stain elongated papillae, especially with heavy daily consumption.
- Tobacco use: Smoking or chewing tobacco is one of the strongest risk factors. Tar and nicotine residue cling to papillae and feed pigment-producing bacteria.
- Heavy alcohol use: Alcohol dries out the mouth and changes the bacterial balance, both of which encourage papillae overgrowth.
- Antibiotics: Several types, including those in the tetracycline family, erythromycin, amoxicillin-clavulanate, metronidazole, and linezolid, can disrupt the normal balance of bacteria in your mouth. When the usual bacterial population is knocked back, pigment-producing organisms can take over.
- Antiseptic mouthwash: Chlorhexidine, a prescription-strength mouthwash often used after dental procedures, reacts with tannins in food and drinks to produce dark brown or black staining on teeth and tongue.
Poor oral hygiene ties all of these together. When you don’t brush your tongue regularly, dead cells and debris accumulate faster than they’re removed, giving pigments more surface area to cling to.
Who Gets It
Black hairy tongue is more common than most people realize. Prevalence ranges from about 8% in younger adults to as high as 57% in certain high-risk populations. Men are affected more often than women. The condition becomes more common with age, likely because older adults have had more cumulative exposure to the habits that trigger it: years of coffee drinking, tobacco use, or medication use. If you’ve had it before, you’re more likely to get it again.
How to Get Rid of It
The good news is that black tongue typically resolves on its own once you address what caused it. If bismuth was the culprit, the staining fades within a few days without any intervention. For black hairy tongue from other causes, a few simple changes speed up the process significantly.
Start by gently brushing your tongue twice a day with a soft-bristled toothbrush, or use a flexible tongue scraper. This physically removes the dead cells, trapped bacteria, and food debris that are holding the pigment. Brush your tongue after meals when possible. Cut back on coffee, tea, and alcohol if you’ve been consuming them heavily. If you use tobacco, reducing or stopping will make a noticeable difference.
If you recently started an antibiotic and noticed the discoloration shortly after, the tongue should return to normal once you finish the course. Don’t stop your antibiotic early over this. If you’re using a chlorhexidine mouthwash, the staining will clear after you stop using it, though it may take a week or two of regular tongue brushing.
When It’s Something Else
In rare cases, a dark tongue can signal something beyond the usual black hairy tongue. If the discoloration doesn’t respond to brushing and habit changes within a couple of weeks, or if it’s accompanied by pain, bleeding, open sores, or difficulty swallowing, those are signs worth getting evaluated. A persistent dark patch that doesn’t scrape off could occasionally represent a different type of lesion that needs a closer look. But for the vast majority of people who wake up startled by a black tongue, a toothbrush and a look at what they ate, drank, or took the night before will explain it.