Hairy tongue is an elongation and hypertrophy of filiform papillae. It should not be confused with oral hairy leukoplakia, a viral condition seen in immunocompromised patients. It is associated with tobacco use, poor oral hygiene, and antibiotic use.
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Reamy BV, Derby R, Bunt CW. Common tongue conditions in primary care. American Family Physician. 2010;81(5):627-634.