Finding an unexpected dark spot on the tongue can cause immediate concern, as the oral cavity is not typically a site for noticeable pigment changes. This discoloration, which can range from a light brown macule to a black, textured patch, prompts many to search for answers regarding its cause. While some spots are the result of completely harmless external factors, others may indicate the need for a professional medical evaluation.
Temporary and Environmental Factors
Many dark spots on the tongue are temporary and result from extrinsic factors. Extrinsic staining is a common culprit, occurring when pigments from dark-colored foods and beverages, such as coffee, tea, red wine, or berries, are deposited onto the tongue’s surface. Tobacco use, particularly smoking, introduces tar and nicotine that can also stain the tongue, sometimes leading to persistent discoloration.
Black Hairy Tongue (Lingua Nigra Villosa) is a typically benign cause. This condition is characterized by the elongation and hypertrophy of the filiform papillae, which are the small, thread-like projections covering the tongue’s surface. These overgrown papillae fail to shed normally, creating a dense, hair-like mat that traps food debris, bacteria, and staining substances. The resulting appearance is a dark brown or black patch, often located on the central portion of the tongue’s dorsal surface.
Trauma can also lead to temporary dark spots. This trauma can cause a localized bruise, or hematoma, where blood pools beneath the mucosal surface, appearing as a dark, bluish-black spot that resolves naturally as the body reabsorbs the blood. Certain over-the-counter medications, such as antacids containing bismuth, can also temporarily react with saliva and sulfur in the mouth to create a reversible black discoloration.
Intrinsic Pigmentation and Drug Reactions
Physiological pigmentation, or racial pigmentation, is a common and harmless phenomenon caused by increased melanin deposition by melanocytes within the oral mucosa. These lesions, often presenting as flat, stable, brown or black spots, are more prevalent in individuals with darker skin tones and do not require treatment.
Another localized cause is the amalgam tattoo. This occurs when silver amalgam particles from dental fillings become inadvertently implanted into the soft tissue during dental procedures. Amalgam tattoos appear as blue, gray, or black macules, and while they can occur anywhere in the oral cavity, they are most often seen near sites of previous dental work.
A variety of prescription medications can also induce hyperpigmentation of the oral tissues as a side effect. The antibiotic minocycline is well-known for causing a blue-gray or black discoloration on the tongue and other mucosal surfaces due to the deposition of drug metabolites. Antimalarial drugs, such as chloroquine, and certain psychiatric or chemotherapeutic agents can also lead to diffuse pigmentation in the mouth, which may persist even after the medication is discontinued.
Oral Manifestations of Systemic Disease
Less frequently, a dark spot on the tongue serves as an early indication of a widespread underlying medical condition. Addison’s disease, a form of primary adrenal insufficiency, often presents with hyperpigmentation of the skin and mucous membranes. This condition leads to an overproduction of ACTH, which stimulates melanocytes, causing an increased synthesis of melanin. This manifests as patchy, blue-black or brown macules in the mouth, including the tongue.
Another condition is Peutz-Jeghers Syndrome (PJS), a rare genetic disorder characterized by pigmented spots on the lips and oral mucosa. The lesions are small, blackish-brown macules that are often present from childhood and appear irregularly distributed over the lips, buccal mucosa, and sometimes the tongue. Finding these characteristic spots in the mouth can be an important diagnostic clue, as it prompts the need for surveillance of the associated intestinal polyps.
Neurofibromatosis can also occasionally manifest with multiple small, dark spots, known as café-au-lait macules, on the skin and oral mucosa. While less common on the tongue than other oral sites, the presence of these pigmented lesions suggests an underlying genetic mechanism affecting cell growth and pigmentation. When the cause of oral pigmentation is unclear, especially when diffuse or multifocal, a systemic disease must be considered as part of the differential diagnosis.
Signs That Require Professional Evaluation
While many dark spots are benign, certain features signal the potential for a more serious condition, necessitating prompt evaluation by a dentist or physician. Any dark spot that persists for longer than two weeks, even after eliminating potential environmental causes like staining foods or tobacco, should be professionally examined.
A spot that rapidly increases in size, changes its shape, or develops irregular, poorly defined borders requires immediate attention. Any dark lesion that exhibits color variegation raises suspicion. Associated symptoms such as pain, tenderness, bleeding, ulceration, or the development of a raised, lumpy texture are also significant indicators of a possible pathological process.
The professional evaluation is designed to rule out rare but serious conditions, most notably oral melanoma, which can appear as a dark, irregular spot on the tongue. In cases where the clinical appearance is ambiguous or suspicious, a biopsy is often performed to obtain a definitive diagnosis and determine the appropriate course of action. Early detection of any malignant or precancerous lesion improves the prognosis.