The tongue is an excellent indicator of your overall health. Black stains and dark discolourations on the tongue can indicate a variety of things, such as reactions to a medication or even certain types of cancer. It is important to seek medical attention if you notice any dark spots on the tongue, and to let your doctor determine whether or not treatment is necessary.
Reaction to Medications
A reaction to medication is the most common cause of black stains on the tongue. Bismuth medications like Pepto-Bismol can temporarily turn the surface of the tongue black. Normal brushing should remove these stains, but if they persist, seek medical treatment.
Hyper-pigmentation is one cause of black stains on the tongue, and is usually a non-harmful genetic condition. Black spots appear on the top or underneath the tongue, and can be treated by a dermatologist for cosmetic reasons.
A "hairy" tongue is usually covered in small black spots instead of larger black patches. This can be caused by tobacco consumption or antibiotics, or could be the result of a fungal infection called glossophytis.
In rare cases, the black stains on the tongue could indicate oral cancer. Cancerous tissues can cause discolourations in the mouth, but are usually accompanied by a small bump near the dark area.