A black or dark appearance under your tongue is almost always caused by enlarged veins, a harmless and extremely common condition that becomes more likely as you age. Less often, the discoloration comes from something you ate or a medication you’re taking, tobacco use, a bruise, or leftover pigment from dental work. In rare cases, a dark spot that grows, bleeds, or doesn’t go away can signal something more serious that needs professional evaluation.
Enlarged Veins Under the Tongue
The most common explanation for dark blue, purple, or blackish coloring under the tongue is sublingual varicosities, which are simply swollen veins on the underside of the tongue or the floor of the mouth. They look like twisted, raised, irregular lines or clusters and can appear blue, purple, or so dark they look nearly black. They’re soft to the touch and typically painless.
These veins are rare in younger people but become increasingly common after age 60. One study of nursing home residents found a prevalence of nearly 57%. In the general population, estimates range from about 16% to 70% depending on the age group studied, with the highest rates in people in their 70s and 80s. The veins develop because blood vessels and the connective tissue around them change with age, and blood pressure within small vessels gradually increases.
Smoking, wearing dentures, and having cardiovascular disease all raise the odds. One study found that cardiovascular disease was the strongest risk factor, roughly quadrupling the likelihood of developing these enlarged veins. They don’t require treatment and aren’t dangerous on their own, though your dentist may note them during a routine exam.
Medications That Stain the Tongue Black
If you’ve recently taken a pink, chalky antacid containing bismuth (the active ingredient in Pepto-Bismol), that’s a very likely culprit. Bismuth reacts with sulfur compounds in your saliva and the food you eat, forming a dark-colored deposit on the surface of the tongue. The result can look alarming, sometimes turning the tongue or the tissue under it jet black, but it’s completely harmless. The discoloration fades on its own once you stop taking the medication, usually within a few days.
Tobacco Use and Dark Pigmentation
Smoking or chewing tobacco can trigger the mouth’s lining to produce extra melanin, the same pigment responsible for skin color. This response, called smoker’s melanosis, is the body’s attempt to protect tissue from harmful chemicals in tobacco smoke, particularly nicotine and benzpyrene. The darkened patches tend to show up on the gums, inner cheeks, lips, and floor of the mouth, and they can extend to the underside of the tongue.
The pigmentation is directly tied to tobacco exposure. People who smoke heavily for years develop more pronounced discoloration. The good news: quitting smoking leads to a gradual disappearance of the dark patches over time.
Natural Melanin Pigmentation
Some people naturally have darker pigmentation inside their mouths, just as skin tone varies from person to person. This is genetically determined, more common in people with darker skin, and completely normal. A study of a South African population found that 54% of Black participants, 21% of white participants, and 16% of Indian participants had visible oral melanin pigmentation. The gums are the most frequently affected site (about 73% of cases), but the pigmentation can appear anywhere in the mouth, including under the tongue. These spots are typically symmetrical, stable in size, and have been present for as long as you can remember.
Bruising Under the Tongue
A sudden dark purple or black area under the tongue can be a sublingual hematoma, essentially a bruise. This can happen after biting your tongue, dental procedures, or minor trauma. It’s also seen in people taking blood-thinning medications like warfarin, where even slight irritation can cause bleeding under the tissue. The area may feel swollen or tender. Most small hematomas resolve on their own within a week or two, similar to a bruise anywhere else on your body. A large or rapidly expanding hematoma, especially one that pushes the tongue upward or makes breathing difficult, needs emergency attention.
Dental Amalgam Tattoos
If you’ve had silver dental fillings, tiny particles of amalgam can become embedded in the soft tissue of your mouth during dental work. This creates a flat, dark gray or bluish-black spot that doesn’t change in size or shape over time. These spots, sometimes called amalgam tattoos, are most often found on the gums or the floor of the mouth near a restored tooth. They’re permanent but completely benign. Your dentist can usually identify one on sight based on its location relative to your dental work.
Signs That Need Professional Evaluation
Most causes of dark coloring under the tongue are harmless, but certain features warrant a closer look. A dark spot that is growing in size, has irregular or uneven borders, bleeds without obvious cause, or is accompanied by a lump or sore that won’t heal could indicate a more serious condition. Mucosal melanoma, a rare cancer that can develop on the lining of the mouth, may appear as a dark, growing lesion. Symptoms can include a lump on the tongue that keeps getting larger, a sore that doesn’t heal, unexplained mouth pain, or spontaneous bleeding.
The key differences between harmless discoloration and something concerning come down to change and symmetry. Enlarged veins are soft, compressible, and symmetrical on both sides of the tongue. Natural pigmentation is stable and has been there for years. A new spot that appeared recently, is only on one side, or is changing in color, size, or texture is worth showing to a dentist or doctor. If you have tongue discoloration that lingers or doesn’t improve with better oral hygiene, schedule an appointment to have it evaluated.