Is black hairy tongue dangerous?

no: Many people have black or even white hair tongue-some various causes-anemia-gastric upsets -heavy smokers -radiation treatment-not dangerous- brush tongue to keep it clean.

No: The tongue is coated with taste receptors termed papillae. These normally stay short from food chewing and constant rubbing in normal activity of the mouth. If they grow longer, they can be stained darker by food and other substances in the mouth. It is not harmful and is not pathologic. You can lessen it by brushing the tongue as well as your teeth with your toothbrush.