The tongue is usually coated with tiny structures that aid in tasting, these are called taste buds, one variety of these are papillae which are commonly involved in the causation of yellow tongue. Yellow tongue is a harmless condition that cured on its own in most cases, but may persist in rare instances. Yellow tongue is the infestation of bacteria within the mouth. 

Yellow tongue usually occurs as a result of a harmless buildup of dead skin cells on the tiny projections (papillae) on the surface of your tongue. The bacteria that infest the papillae produce pigment, thus staining the tongue. Longer than usual papillae can trap cells and are prone staining by tobacco or other foods.

The yellowish discoloration can occur anywhere over the tongue, on the back of tongue, tip of tongue or over the sides. The symptoms are: the visually yellow-coated tongue, bad breath, bad taste, cold or dry mouth, irregular surface of the tongue, bumpy tongue, red and fiery tongue, and furry tongue. 

The causes of yellow tongue: it is the first stage of Hairy tongue infested by Candida albicans, regular intake of antibiotics or corticosteroids, excessive use of alcohol-based mouthwash, habitual mouth breathing or due to blocked airways causes drying up of tongue, due to smoking, and due to systemic infections such as HIV infection, fever, liver or gallbladder disease and jaundice.

Self-care is the best treatment, regular cleaning of tongue with tongue scrapers. Intake of high-fibre foods such as fruits and vegetables help in keeping the tongue clean. Gargling with alcohol-free mouthwashes reduces the tooth-decay and discoloration of tongue. See a doctor if yellow tongue does not subside with these measures and if there is yellowish discoloration of eyes, suggesting jaundice.

-Koya Satyasri