Black Hairy Tongue Black hairy tongue has been referred to by various names, including hyperkeratosis of the tongue, lingua villosa nigra, nigrities linguae, keratomycosis linguae and melanotrichia linguae.  Reports of cases of black hairy tongue go back many centuries. Lusitanus (1557) is credited with the original description of black hairy tongue. He reported having found hairs on the tonge of a man, which when "pulled out would renew themselves." [1, 2]
The medical literature contains relatively little information about this entity. No controlled studies have been performed, and the cause of the condition remains unknown.
A 36-year-old woman presented to her physician with the complaint of a "color and film" on her tongue, which she had first noticed approximately seven days earlier. The patient stated that the symptoms began after she had completed a week-long course of metronidazole prescribed for Gardnerella vaginalis vaginitis. She denied pain but stated that her tongue felt "thick." She became alarmed when she examined her tongue in the mirror and observed the apparent growth of black hairs. The patient did not smoke or drink. She was not receiving any medications on a regular basis and had been in good health.
Examination of the oral cavity revealed good hygiene. Close examination of the dorsum of the tongue (Figure 1) disclosed elongated filiform papillae with black discoloration. The tip and the sides of the tongue were not involved.
A diagnosis of black hairy tongue was made, and the patient was advised to brush her tongue twice daily with a soft-bristled toothbrush. The patient's symptoms resolved over the following weeks (Figure 2).
The patient saw another physician at the same office a few months later and was treated with a 2-g dose of metronidazole for Trichonomonas vaginalis vaginitis. Black hairy tongue did not recur.
Estimates of the prevalence of black hairy tongue vary with the population studied. Farman  estimated an incidence of 0.15 percent in the general population. His study revealed an increased incidence in the elderly (0.72 percent) and a surprisingly high incidence in cancer patients (22 percent).
Black hairy tongue is easily differentiated from other benign tongue conditions (Table 1). The characteristic appearance is usually restricted to the dorsum of the tongue, immediately anterior to the circumvallate papillae. It rarely involves the tip or sides of the tongue. [4h The "hairlike" appearance results from elongation of the filiform papillae. The color of the papillae ranges from brownish black to yellowish brown.
Electron microscopic studies have confirmed that the lengthening of the filiform papillae is due to accumulated keratinized layers.  Normal filiform papillae are approximately 1 mm in length. The papillae in black hairy tongue may reach a length of 12 to 18 mm.  Despite this marked hyperplasia of the papillae, no cellular atypism has been found. Fungi, bacteria and debris are commonly noted between the keratinized layers.
Tru black hairy tongue, in which the filiform papillae are elongated, must be distinguished from "pseudohairy tongue," in which there is brownish black discoloration of the tongue without the associated hypertrophied papillae. [6, 7] Pseudohairy tongue may be caused by certain foods (especially fruits and candies), alcohol (particularly red wines), various drugs (especially those containing iron), some mouthwashes and tobacco.
Most patients with black hairy tongue are otherwise asymptomatic, and visits to the physician are prompted primarily by aesthetic concerns. Occasionally, the papillae are so elongated that the patient experiences gagging and irritation. Rarely, patients may complain of a metallic taste. Some have noted a foul taste and odor, which have been attributed to the breakdown of food debris within the "hairs." 
Little is known about the etiology of black hairy tongue. Although Candida and Aspergillus species can frequently be isolated, they are not believed to be the causative agents. [9-11] One theory suggests that limitation of tongue movements (from illness or painful oral conditions) is responsible for the development of hairy tongue. The lack of tongue movements prevents the normal desquamation of the keratinized surface layers of the filiform papillae through "friction of the tongue with food, the palate and the upper anterior teeth."  Several authorities have suggested that the black discoloration results from the growth of pigment-producing organisms in the oral cavity. [2, 7, 13, 14]
Many investigators have noted that patients with black hairy tongue have an acidic tongue (pH or 6 or less.) [2, 3, 15] Black hairy tongue itself may be responsible for the low pH by causing retention of food particles, including sugars, which are fermented by bacteria to form acids. 
Other conditions that have been associated with black hairy tongue include prolonged use of oxidizing agents (such as sodium perborate, sodium peroxide and hydrogen peroxide, commonly contained in mouthwashes), excessive use of tobacco, oral or parenteral antibiotic therapy, phenothiazines, griseofulvin, vegetable colorings, vitamin deficiency, gastrointestinal disorders and poor oral hygiene. An association with radiotherapy has been reported in cancer patients. 
In a 1925 study, Prinz  suggested that black hairy tongue results from a constitutional state that predisposes the surface of the tongue to irritation by specific substances. The irritation leads to hypertrophy of the filiform papillae, with secondary deposits of pigments. Prinz believed that the main source of these pigments was a local reaction between the decomposition products of food debris and the iron present in the minute amounts of blood that can be found in the mouth. To verify this theory, he applied an irritant (tincture of nut galls) twice daily to the tongues of six students. Within a week, one student showed a slight enlargement of the filiform papillae of the tongue. Prinz then had the student injure his gums slightly with a toothpick to allow blood to come in contact with the tongue. A marked enlargement of the papillae occurred and a deep brown stain was noted.
Although black hairy tongue may resolve spontaneously, various therapies have been proposed. Paradoxically, some of the suggested treatments have also been mentioned as possible causative agents. Any predisposing factors (tobacco, strong mouthwashes, antibiotics, etc.) should be eliminated. The patient should stop all use of candy drops or breath mints and practice scrupulous oral hygiene. The tongue should be brushed at least twice daily with a soft toothbrush and a 3 percent hydrogen peroxide solution or baking soda.
Topical triamcinolone acetonide (Aristocort, Kenalog, Mytrex, etc.), applied twice daily after wiping the tongue dry, has been successful in some patients.  Multivitamin complex and vitamin B preparations have been used,  as have topical antifungal agents.  Yogurt or other Lactobacillus acidophilus cultures may be of benefit.  Clipping of the elongated papillae (using local anesthesia) or surgical excision of the papillae is rarely required.
Of historical interest is the use of keratolytic agents to treat black hairy tongue. Podophyllin suspension in acetone and alcohol,  trichloroacetic acid,  salicylic acid,  and a 40 percent solution of urea in water  have been applied to the tongue with varying degrees of success. Because of the potential for local irritation and problems related to systemic absorptiono, these keratolytic agents are not recommended for routine use.
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GERALYN M. SARTI, M.D. is associate director of the St. Elizabeth Family Practice Residency, Dayton, Ohio, and associate clinical professor of family practice at Wright State University School of Medicine, also in Dayton. A graduate of the University of Michigan Medical School, Ann Arbor, Dr. Sarti completed a residency in family practice at St. Joseph Hospital, Flint, Mich.
RICHARD I. HADDY, M.D. is associate professor and director of research and scholarly activities in the Department of Family Medicine at Wright State University School of Medicine.
DENNIS SCHAFFER, D.D.S. is director of the dental clinic at St. Elizabeth Medical Center, Dayton, and assistant clinical professor of family medicine at Wright State University School of Medicine.
JOHN KIHM, M.D. is in private practice in Westchester, Ohio. Dr. Kihm received his postgraduate training at the St. Elizabeth Family Practice Residency.
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