A black, coated tongue is a temporary, harmless condition typically resulting from 
an overgrowth of bacteria and sometimes yeast in the mouth. These organisms accumulate on the tiny projections of the tongue — called papillae — and cause discoloration. Certain types of bacteria and yeast make red blood cell pigments (porphyrins), which can give the tongue a black appearance. In some cases, the tongue may also appear "hairy" due to more rapid growth of papillae or an interruption of the normal shedding of cells by the tongue.
an overgrowth of bacteria and sometimes yeast in the mouth. These organisms accumulate on the tiny projections of the tongue — called papillae — and cause discoloration. Certain types of bacteria and yeast make red blood cell pigments (porphyrins), which can give the tongue a black appearance. In some cases, the tongue may also appear "hairy" due to more rapid growth of papillae or an interruption of the normal shedding of cells by the tongue.In some cases, the cause of black, coated tongue can't be determined. However, some potential causes include:
Changes in the normal bacteria or yeast content of the mouth following antibiotic treatment.
Poor oral hygiene .
Some tips for removing the discoloration include:
Gently brush your tongue with a toothbrush twice a day.
Rinse your mouth with diluted hydrogen peroxide (one part peroxide to five parts water) or apply it with a toothbrush. Rinse out your mouth afterward.
If this doesn't resolve the problem, consult your dentist or doctor. If the discoloration is due to bacterial overgrowth, antibiotics may be prescribed.
Other causes of tongue discoloration include:
Medications containing bismuth, such as Pepto-Bismol
Regular use of mouthwashes containing oxidizing agents, such as peroxide, or astringent agents, such as witch hazel or menthol
Tobacco use
Drinking excessive amounts of coffee or tea.
Adapted from : Mayo Foundation for Medical Education and Research
