It's not always possible to figure out the cause of black hairy tongue. However, potential causes include:
- Changes in the normal bacteria or yeast content of the mouth following a course of antibiotics (the oral cavity normally has harmless bacteria)
Poor oral hygiene
Regular use of mouthwashes that contain oxidizing agents, such as peroxide, or astringent agents, such as witch hazel or menthol
Irritation due to drinking hot beverages, such as coffee or tea
If any of the above listed causes is pertinent to your case, then you will need to omit it from your regular practices. It's always a good idea to visit your dentist's clinic.