What causes black tongue in an otherwise healthy adult?

What Causes Black Tongue

Black hairy tongue is caused by defective desquamation (shedding) of the filiform papillae on the dorsum of the tongue, leading to elongated papillae that accumulate pigment-producing bacteria, fungi, food debris, and chromogenic substances. 1, 2

Primary Mechanism

• The condition results from elongation of filiform lingual papillae (normally 1mm, can extend to 12-18mm) due to impaired keratin shedding, creating a characteristic carpet-like or hairy appearance. 1, 3
• The accumulated papillae trap chromogenic bacteria, fungi (especially Candida species), food particles, and pigments that cause the black, brown, or dark discoloration. 1, 3
• This is a benign, self-limiting condition with excellent prognosis that typically resolves with removal of predisposing factors. 1, 2

Major Predisposing Factors

Medications (Most Common Iatrogenic Cause)

• Antibiotics are the most frequently implicated medications, particularly doxycycline, erythromycin, amoxicillin-clavulanate (co-amoxiclav), metronidazole, and piperacillin-tazobactam. 2, 3
• Antipsychotic medications have been associated with black hairy tongue development. 3
• Onset typically occurs within a few days to 5 weeks after starting the offending medication. 2

Lifestyle and Behavioral Factors

• Smoking is one of the most common predisposing factors in adults. 1, 3
• Excessive coffee or black tea consumption contributes to pigment accumulation and tongue discoloration. 1
• Poor oral hygiene allows bacterial and fungal overgrowth with inadequate mechanical debridement. 1, 3

Medical Conditions

• Xerostomia (dry mouth) from any cause reduces natural cleansing mechanisms. 1
• Immunocompromised states increase susceptibility to fungal and bacterial colonization. 3
• General debilitation or medical conditions limiting ability to maintain oral hygiene. 1, 3
• Trigeminal neuralgia has been associated with black hairy tongue. 1

Other Contributing Factors

• Vitamin C supplementation has been reported as a trigger, even in infants as young as 28 days old. 4
• Alcohol consumption may contribute to the condition. 2

Clinical Presentation

• Most cases are asymptomatic, though patients commonly present with aesthetic concerns about the tongue appearance. 1, 2
• When symptomatic, patients may experience burning mouth syndrome, halitosis (bad breath), nausea, gagging, or dysgeusia (altered taste). 1
• The condition affects 0.6% to 11.3% of the population depending on geographic location. 1, 2

Diagnosis

• Clinical diagnosis relies on visual observation of the characteristic elongated, discolored papillae on the dorsal tongue surface. 1, 2
• Detailed history taking to identify medications, smoking, dietary habits, and underlying medical conditions is essential. 1, 3
• Microscopic evaluation may occasionally be performed but is rarely necessary. 1
• In infants or atypical presentations, consider histological evaluation to exclude pigmented lesions of oral mucosa, acanthosis nigricans, oral hairy leukoplakia, or congenital melanocytic lesions. 5

Treatment Approach

The definitive treatment is identification and discontinuation of the causative agent combined with mechanical debridement. 1, 2

Immediate Management

• Identify and stop the offending medication if possible (consult prescribing physician before discontinuing antibiotics or other essential medications). 2, 3
• Initiate gentle tongue brushing or scraping 2-4 times daily to promote desquamation and remove accumulated debris. 1, 3, 4
• Reassure the patient about the benign nature of the condition to reduce anxiety. 1

Supportive Measures

• Improve oral hygiene practices with regular brushing and use of antiseptic mouthwashes. 1, 3
• Eliminate modifiable risk factors including smoking cessation and reducing coffee/tea consumption. 1, 3
• Address xerostomia if present with saliva substitutes or treatment of underlying causes. 1

Expected Timeline

• Partial resolution typically occurs within 4 weeks of initiating tongue brushing and removing predisposing factors. 4
• Complete resolution may take longer depending on the severity and duration of the condition. 1

Critical Pitfalls to Avoid

• Do not misdiagnose as oral candidiasis (thrush) and prescribe unnecessary antifungal treatment without proper examination—this delays appropriate management and exposes patients to unnecessary medications. 4
• Do not assume the condition requires systemic treatment—black hairy tongue responds to local mechanical measures and removal of causative factors. 1, 2
• Do not overlook medication history, particularly recent antibiotic courses, as this is the most common iatrogenic cause in otherwise healthy adults. 2, 3
• In infants with persistent tongue lesions, always obtain a thorough dietary and supplement history, as vitamin C supplementation has been implicated even in very young patients. 4