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Why Do Dogs Foam at the Mouth?

You're unlikely to encounter poisonous toads at the dog park, but they're one alarming reason why a dog might be foaming at the mouth!

Melvin Peña  |  Apr 12th 2016


Say “rabies,” and likely the first image that pops to mind is a dog whose oral cavity is bedewed with white, viscous froth. Foaming at the mouth is the most recognizable symptom of furious rabies. This ancient viral disease is not the only reason why thickened saliva accumulates around a dog’s mouth, though it is easily the most preventable. There are a number of causes; those we’ll explore here include:

  • Rabies
  • Epilepsy
  • Licking or eating poisonous amphibians
  • Anxiety and overactivity

In some cases, a bit of foam along the sides of a dog’s mouth will be the least alarming change in your dog’s normal routine. If a dog’s foaming mouth is an area of concern, several of the causes enumerated here can be avoided, either through vaccination, diligence, or situational awareness.

dog foaming at mouth

One iconic symptom of rabies is foaming at the mouth . (Photo by Ben Fruen on Flickr)

Rabies

One reason that the rabies virus is so entrenched in our minds as a source of foam in a dog’s mouth is our history with it. First described over 4,000 years ago on clay tablets, rabies and our image of rabid canines are persistent problems. The disease is most commonly transmitted through bites from infected animals, though saliva carrying the virus simply needs to enter an open wound or cavity to take hold. It’s formerly known as “hydrophobia,” and once a dog is infected, one of the virus’s mechanisms is to restrict access to water.

With a dry mouth and a brain that is starting to swell, saliva begins to gather around the exterior of a dog’s mouth. There are two forms of rabies, furious and paralytic, and each causes noticeable changes to both the body and behavior. Normally frisky and energetic dogs can become listless and unresponsive. Normally quiet and placid dogs may start acting aggressive and short-tempered. High fever is associated with both forms of rabies, which is the immune system’s attempt to kill or delay the reproduction of the virus.

Since rabies is difficult, if not impossible, to cure once it has infected a dog, keeping your dog’s rabies vaccination current is the simplest way to avoid an untimely demise. According to the World Health Organization, “in up to 99 percent of human cases, the rabies virus is transmitted by domestic dogs.” They get it from contact with infected wildlife. If you live in an area where bats, foxes, raccoons, or skunks are native, getting your dog vaccinated is critically important.

Epilepsy in dogs

Whereas rabies has one cause that is easy to pinpoint and prevent, the causes of epileptic seizures in dogs can be more difficult to isolate and manage. Part of the difficulty is that there are a variety of sources for seizures, including accidental trauma and genetics. No matter the cause, the longer seizure activity persists, the more physical damage is incurred by the dog’s brain, and the harder it is treat, manage, or resolve.

dog foaming at mouth

The Colorado River toad’s venom can cause a dog to foam at the mouth. (Photo via Wikimedia Commons)

Canine seizures tend to occur early in mornings or late in evenings while the dog is sleeping or resting, and they have a usual duration of 30 seconds to a couple of minutes. In dogs who are up and about, a seizure causes dramatic physical changes, not limited to muscles twitching and convulsing. An upright dog may collapse on his side and begin pawing the air, urinate or defecate involuntarily, and either bite at nothing repeatedly or clench his jaw. As the dog is deprived of motor control and overheating, his mouth starts to dry and foam emerges from the sides.

Consult a veterinarian at the first signs of seizure activity. Certain dog breeds are at greater risk for developing symptoms of idiopathic epilepsy — a term that means that beyond inherited risk, the actual cause is unknown — including Beagles, Retrievers (Golden and Labrador), and Vizslas. In these cases, signs tend to emerge during the first three years of life, so it’s worth being observant and discussing what to do with your vet in the event of a seizure.

Licking or eating poisonous toads

Small woodland mammals that might be infected with rabies are relatively easy to avoid if you encounter one on a forest stroll with a dog, or if the dog is vaccinated. There are more insidious and intriguing creatures out there, though, and ones you might not suspect of harboring lethal toxinsThe best news about the cane toad (also known as the marine toad) and the Colorado River toad (or Sonoran Desert toad) is that most of our dogs are extremely unlikely to have them in our neighborhoods.

In the United States, the cane toad is found primarily in Florida and Southern Texas, while the Colorado River toad’s habitat ranges only from southern California to New Mexico. Dog owners who live or spend winters in these areas should exercise caution, particularly during dawn and dusk dog walks. Scavengers, these poisonous toads may also encroach on your yard if dog kibble or other food remnants are readily available. 

dog foaming at mouth

Exercise-related dehydration can easily cause dogs to foam at the mouth. (Photo via Shutterstock)

Unlike rabies, in which infected carriers spread the disease through aggression, the toad’s venom is not an attack, but a defense mechanism. When these toads are bothered or threatened, even by a dog’s simple curiosity, they secrete the toxin through their skin. The effects are almost immediate, resembling seizure activity, right down to excessive drooling and foaming at the mouth. The faster you get a toad-poisoned dog to a vet, the better.

Stress and overactivity

As a dog health problem, anxiety manifests in a variety of ways. From destructive behaviors such as digging and chewing to ingesting non-food items and digestive upset, stressors of all kinds can provoke strange reactions from dogs. Whether your dog gets nervous during car travel, suffers from separation anxiety, or isn’t getting sufficient exercise, sudden periods of stress can cause dogs to foam at the mouth.

On the opposite side of the spectrum, if your dog isn’t properly hydrated when you head to the dog park or the trails for a run, excessive activity and lack of water is just as likely to produce a frothy mouth. If you’re headed out for extended stretches of intense physical activity, make certain that there are readily available sources of water on site, or take a portable bowl or dish along for the adventure. A dog deals with heat by panting, and the more they pant, the more moisture is lost to the air. Whatever saliva remains congeals into that familiar white foam around their mouths and lower jaw.