A condition called black hairy tongue, which is caused by excess yeast or bacteria growth in the mouth, can turn the tongue green as well as black, brown or yellow, according to WebMD. Dry mouth is one potential cause of the condition, indicates Mayo Clinic. Dehydration is also associated with both dry mouth and black hairy tongue.
Other conditions and habits that make the occurrence of black hairy tongue more likely include tobacco smoking; poor oral hygiene; radiation therapy of the head and neck; and the use of mouthwashes containing menthol, peroxide or witch hazel, explains WebMD. Certain medications can also cause black hairy tongue, including antibiotics and medications that contain bismuth.
Good oral hygiene is the best treatment for black hairy tongue, states WebMD. Doctors recommend brushing both the teeth and the tongue twice daily with a soft toothbrush. A tongue scrapper can ensure a more thorough cleaning. Smokers should quit the habit to improve the condition. If oral hygiene does not solve the problem, a doctor can prescribe antibiotics, antifungals or topical medications such as tretinoin. In more severe cases, if all other treatments have failed, the doctor may recommend electrosurgery or laser surgery to clip off the affected papillae.