Imagine looking into the mirror and discovering that your tongue has turned black. While unsightly and frightening, a black tongue is usually temporary and the causes behind it are not a health risk.
Your tongue can turn black if you have eaten something that has stained it. Black liquorice can stain your tongue, as can chewing tobacco. Products that contain bismuth can temporarily turn your tongue black, according to "Atlas of Adult Physical Diagnosis."
If you have a black tongue, then you could have a fungus called Aspergillus niger growing on the surface of your tongue. If you have too much bacteria growing in your mouth, it could cause your tongue to appear black and hairy, according to the Mayo Clinic.
Temporary staining of your tongue will clear up once you stop using whatever product is causing the blackening of your tongue. Fungus or bacteria on your tongue that turn it black will also clear up with time if you practice improved oral hygiene.