Black Tongue Caused by Malnutrition

Malnutrition is a leading cause of turning a dog's healthy pink tongue to black.
Malnutrition is a leading cause of turning a dog's healthy pink tongue to black. (Image: Image by, courtesy of josh)

As in human beings, a black tongue in canines can be caused by several factors, some of which pertain to malnutrition. Black tongue disease, or pellagra as it is known in human beings, can result from a lack of niacin in the body due to malnutrition. While the condition may look severe, black tongue disease can be treated with vitamin supplements or adjustments to a canine’s nutrition.


Black tongue disease has been studied for years by animal researchers. One of the earliest such studies was done by C.J Koehn Jr. and C.A Elvehjem from the Department of Agricultural Chemistry at the University of Wisconsin, Madison. In their article “Studies on Vitamin G (B2) and its Relation to Canine Black Tongue 1,” Koehn and Elvehjem suggest that, as with humans, a black tongue in canines results from a lack of niacin in the diet.


The main cause of black tongue disease in canines is a lack of niacin in the diet. While this may be a result of malnutrition, it is more likely because the dog simply is not getting enough meat and meat byproducts in its diet. Meat and meat byproducts are primary sources of niacin.


In the article “Water Soluable Vitamins—Vitamin C & Vitamin B Complex in Dogs,” veterinarians Race Foster and Marty Smith write, “'Black tongue' and 'sore mouth disease' are the terms used to describe a dog or cat suffering from a niacin deficiency. A pet suffering with black tongue will lose weight, fail to eat, and have red inflamed gums, lips, and inner cheeks. Bloody diarrhea and death may follow. Niacin deficiency is generally encountered when owners formulate their own diets for their pets and do not include meat as part of the ration. Be very careful when trying to convert a pet into a vegetarian. Dogs are omnivores, which means they must eat meats and vegetables.”


If your dog has a black tongue, it is best to consult with your veterinarian to treat the vitamin deficiency. The vet will best be able to advise you on a proper, well-balanced diet for your dog. If your dog exhibits additional symptoms such as loss of appetite, fever, languor or a swelling of the tongue, you should also seek veterinary attention immediately, as your dog may have a more serious, even life-threatening illness.

Black Tongue Disease vs. Normal Skin Pigments

It is important to note that some dogs' tongues are naturally black or spotted. For example, the chow breed has a naturally blue/black tongue, and many other breeds and mixed-breed dogs have spotted black tongues. These tongues should not be confused with black tongue disease, nor does a black tongue mean that a dog is malnourished or lacking niacin. It is instead the natural pigment of the dog’s tongue and is of no harm to the dog.

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