Black hairy tongue is caused by what problems?

See below: Black hairy tongue (in latin, lingua villosa nigra) is usually caused by some sort of rubbing sown of the papilla of the tongue so when they grow back they are longer and look "hairy." th tissue then can get stained by a number of chemical s or drugs like pepto-bismol and look black. Is is also a side effect of bulemia but by itself, it is harmless.

Change in oral flora: Hairy tongue does not result only from poor oral hygiene. Dental offices are full of people with poor oral hygiene - they don't have hairy tongue. Poor hygiene is a big factor, but hairy tongue is caused by a change in the natural bacteria in your mouth. This change is caused by long-term antibiotics, steroids, immune suppression, or a systemic problem. It's not as simple as not brushing 2x daily.