A black, hairy tongue (lingua villosa nigra) occurs when the papilla on the tongue, normally only one mm in length, grow up to 1.5 cm in length and turn black or brown, says Joachim Dissemond of the University of Essen. It occurs most regularly among men who smoke.
The condition may stem from a disturbance in the immune system that allows bacteria to colonise on the tongue. Smoking, especially when combined with poor oral hygiene, certain medicine and vitamin deficits can lead to the black hairy tongue.
Unfortunately, it is difficult to say how long therapy can take. On the one hand, treatment could take years to have an impact and on the other, it could also go away spontaneously, seemingly overnight.