At some point during your time as a dog parent, you have probably experienced the not-so-sweet smell of “doggy breath.” If it’s just the occasional stench coming from your dog’s mouth, it’s probably related to an unsavory eating choice on their part. But if the smell is more of a constant reek than an occasional whiff, it could be a concerning health issue.
One of the reasons for consistently bad breath is advanced kidney failure. We’ll discuss why kidney failure can cause bad breath and list some other medical conditions and non-medical reasons that could lead to your dog’s stinky breath.
The Kidneys Are the Body’s Filters
To understand how failing kidney function can cause bad breath, let’s have a quick anatomy and physiology lesson. Your dog has two bean-shaped kidneys that are tucked up along the spine, near the last ribs. The main function of the kidneys is to filter out and remove waste products from the blood. To do this, each kidney contains hundreds of thousands of nephrons (tiny filtration systems) that filter the blood and remove metabolic waste and toxins from the body via urine. At the same time, the kidneys return important proteins and other substances to the body.
The kidneys play a crucial role in keeping your dog properly hydrated while preserving the correct balance of minerals and electrolytes (e.g., sodium, potassium and phosphorus) that are important for many normal body functions. They are also responsible for producing the hormones that regulate blood pressure (renin) and promote red blood cell production by the bone marrow (erythropoietin). The kidneys also maintain the acid-base balance of the body and convert vitamin D to its active form.
Signs of Kidney Failure
During the early stages of kidney failure, the kidneys can often compensate for their reduced function, which is why dogs don’t usually show any clinical signs. As kidney failure progresses, blood flow to the kidneys is increased to help increase their filtration capabilities, since waste removal is becoming less efficient. This increases urine output which results in increased water intake to keep the dog properly hydrated.
That’s why drinking more and increased urination (frequency and amount) can be some of the first signs of kidney failure. However, because chronic kidney disease has a slow, gradual onset, you may not notice these signs until the condition is quite advanced.
The Link Between Bad Breath and Kidney Failure
The kidneys are responsible for removing waste from the bloodstream, so if the kidneys’ function is failing, it can cause result in a buildup of that waste. One of the waste products that can build up is urea. Excessive urea (called uremia) can cause the dog’s breath to smell like ammonia, urine or even “fishy” when they exhale. Other signs of kidney failure include loss of appetite, increased thirst and urination, weight loss, vomiting, diarrhea and in later stages anemia (pale gums and weakness).
Testing for Kidney Failure
Your veterinarian has kidney disease screening tests they can perform that measure changes in your dog’s blood and urine. Traditional tests use urine specific gravity to measure the kidney’s ability to concentrate urine. They also look for a buildup of the waste products creatinine (from muscle metabolism) and blood urea nitrogen (BUN, a liver byproduct) in the blood. But by the time the waste products can be detected in the blood, the kidneys may have lost 75 percent of their function.
Another test that measures symmetric dimethylarginine (SDMA) may detect kidney disease earlier, when there’s been about 40 percent loss of kidney function, on average. Veterinarians will typically use a combination of the SDMA test along with creatinine, BUN and urine specific gravity to diagnose kidney disease in dogs.
Other Causes of Bad Breath
If your dog’s breath smells like poop, you should first rule out that they didn’t actually… eat poop. If you keep a careful eye on your dog or you’re a meticulous poop-picker-upper and know that isn’t the case, it’s time to investigate other causes — particularly if the smell is constantly there.
The most obvious reason for constantly smelly breath is a dental problem. For example, bad breath is the most common sign of periodontal disease (gum disease). It can also be a sign that your dog has a piece of food or a foreign body stuck in their mouth. Your veterinarian can check if there’s anything lodged in your dog’s mouth and they can also recommend treatment and prevention methods for periodontal disease, like regular at-home teeth brushing and professional cleanings at the veterinary clinic. It’s important to keep your dog’s gums healthy because bacteria can invade under the gumline and enter the bloodstream, where they can infect and damage other organs in the body.
If your dog’s breath has a sweet smell more than a putrid smell, they may have diabetes. Sugary or fruit-smelling breath can be a sign of high blood sugar or even diabetic ketoacidosis, a life-threating metabolic condition that requires immediate medical treatment. Your veterinarian can determine if the sweet breath smell is due to diabetes and recommend treatment options.
Another cause of chronic bad breath is megaesophagus — a condition where the muscles of the esophagus become weak, essentially losing muscle tone and the ability to move food into the stomach. Food and water stay in the esophagus longer before entering the stomach and may be regurgitated if they don’t enter the stomach. In most cases, there is no cure for megaesophagus, but changing the dog’s feeding and eating habits can help reduce the frequency of regurgitation.
Constant bad breath in dogs isn’t normal. If your dog has bad breath as well other signs of kidney failure like increased urination, increased thirst, vomiting or diarrhea, contact your veterinarian immediately. If they have constant bad breath but not the other signs, it’s still important to have them examined by your veterinarian to rule out possible medical conditions.