Hairy tongue, also known as black tongue, refers to an accumulation of keratin on the tips of the filiform papillae of the dorsal tongue. This results in a hair-like appearance of the dorsal tongue. While wet, keratin normally appears white, black, brown, or yellow, the discoloration due to exogenous pigmentation caused by colored foods or drinks; colonization of the keratin by pigment-producing bacteria is often seen.

Keratin is constantly produced by the dorsal tongue papillae, and in the normal situation, the rate at which the keratin is produced is equal to the rate at which it is debrided by normal mechanical actions of chewing and swallowing foods. Anything that disturbs that balance will result in coated or hairy tongue:

• Increased production of keratin can be seen with any irritant, including cigarette smoking, continuous exposure to hot beverages, or excessive brushing of the dorsal tongue.
• Antibiotics, corticosteroids, and antipsychotics are the most common triggering medications.
• Decreased debridement is seen in patients who are edentulous (or have complete dentures) or have chronic hyposalivation for any reason, either of which can cause the patient to select a soft or more liquid diet.
• Patients who have a chronic illness that results in decreased food intake frequently develop a coated or hairy tongue as well.

The patient is often asymptomatic and may be more concerned about the appearance of the tongue. Occasionally, the patient may report a stale taste or malodor. The gag reflex may be triggered if the hairy tongue is posteriorly located and tickles the palate. While some make a distinction between hairy tongue and coated tongue, they are essentially the same process.