A healthy 32-year-old woman presented with 2 weeks of black discoloration of the tongue. She denied new medications and tobacco use, but had started using mouthwash containing hydrogen peroxide 1 month earlier. Examination revealed black pigmentation of filiform papillae on the dorsum of her tongue (Fig. 1). The findings were felt to be consistent with black hairy tongue (BHT) secondary to the use of oxidizing mouthwash. The patient was instructed to discontinue the mouthwash and clean her tongue twice daily with normal saline. Within 2 weeks, the discoloration had resolved.

Figure 1
figure 1

A black to brown discoloration in the posterior aspect of dorsal surface of tongue, associated with elongated and hypertrophied filiform papillae.

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BHT is benign, asymptomatic, and temporary. It presents with black, green, or yellow pigmentation and elongated filiform papillae in a typical carpet-like appearance of the dorsum of the tongue.1 It is believed to be caused by defective desquamation on the dorsal tongue leading to overgrowth of chromogenic bacteria or yeast. BHT is associated with smoking, excessive coffee/tea or alcohol consumption, poor oral hygiene, xerostomia, oxidizing mouthwashes, medications (antibiotics, antipsychotics), and certain medical conditions (HIV, trigeminal neuralgia, malignancies).2 Differential diagnosis includes pseudo-BHT secondary to chemicals or food coloring, pigmented fungiform papillae of the tongue, hairy leukoplakia, and congenital nevi. BHT is usually self-limited and carries a good prognosis.3