Medically reviewed by Brian T. Luong, DMD Several things may cause dark black spots on the tongue, including a benign condition called hairy tongue, some medications, and some health conditions.

Spots on your tongue can signal different conditions depending on the color, shape, ... black hairy tongue: black, gray, or brown patches; may look like they’re growing hair: ...

It was not until the girl’s doctor noted her unusually tan complexion and dark spots under her tongue that it became clear her adrenal glands had stopped working, a potentially fatal health crisis.