5 min read


Why Do Dogs' Jaws Lock



5 min read


Why Do Dogs' Jaws Lock




If you've followed the news at all since Breed Specific Legislation (BSL) began, you have likely heard many different myths purported as fact. Among these myths is the assertion that Pit Bulls are a dangerous breed that should be banned because they possess locking jaws. If indeed this is true, it is frightening and cause for serious concern; perhaps even legitimate enough to at the very least mandate the wearing of muzzles for breeds predisposed to this issue. But is there such a thing as locking jaws? If so, what causes it? Why would certain breeds have this genetic capability and not others? At times, it seems there are more questions than answers. Through a thorough study of canine anatomy and established scientific fact, we can gain powerful insights into the mystique behind "locking jaws." Since much can be learned from considering the wild dog's influence on the modern canine, we can learn a great deal by understanding what dogs use their mouths for and what the purpose of a locking jaw would mean for them.

The Root of the Behavior

Rumors have been swirling for years about the locking jaw theory. Most typically, people attribute this phenomenon to a limited, but very specific, group of breeds. Among the breeds many believe to possess this quality are Boxers, American Staffordshire Terriers, and Bulldogs, though there are many other breeds considered to be "Pit Bull types" that also are credited with being members of the "locking jaw" family. The truth is there isn't a single shred of scientific evidence to support the locking jaw theory in any of these breeds or any breed at all. It is a myth which has become an urban legend. What is a locking jaw? 

Those who insist on the veracity of the locking jaw mechanism in Pit Bulls maintain that dogs of this nature have the ability to snap their jaw into a position that is impossible to be relinquished without the dog's voluntary participation. Many people falsely believe this is part of what makes Pit Bull type dogs, who are often mixes of a variety of breeds as opposed to one purebred faction, predisposed to excel in dog fighting rings. If a dog can latch on to an opponent and lock his jaw in place on a sensitive area like the neck, it is possible for that dog to do immeasurable damage, including possibly killing the dog they are matched against. If this were correct, it would be an invaluable quality to a dogfighter. A ban would then deserve just consideration because dog fighting is both cruel and illegal, but also, a dog capable and programmed for such ferocity would be a potential menace to society at large. 

Prominent researcher Dr. I. Lehr Brisbin has stated that, ‚ÄúThe few studies that have been conducted of the structure of the skulls, mandibles, and teeth of pit bulls show that, in proportion to their size, their jaw structure and thus its inferred functional morphology, is no different than that of any breed of dog. There is absolutely no evidence for the existence of any kind of ‚Äėlocking mechanism‚Äô unique to the structure of the jaw or teeth of the American Pit Bull Terrier.‚Ä̬†What does this mean?

Need advice about your pet's health?

Get answers fast from a veterinary professional 24/7 in the Wag! App.

Get Vet Chat

Encouraging the Behavior

It means a mouth is simply a mouth, and a jaw is simply a jaw. Whether that mouth belongs to a Chihuahua, an Alaskan Malamute, or an American Pit Bull Terrier, the only difference is the size of the bite, not how the jaw itself functions. What does differ is the amount of pressure a dog can exert, and this pressure is dictated by the size of the dog, not by the breed. Obviously, a "power breed" which is a rippling mass of muscle is going to have a stronger bite pressure per square inch than your mother's Pomeranian. It only stands to reason that a breed of size and strength will exert more overall force in an intended bite than a smaller breed. In the absence of any published scientific evidence to corroborate the locking jaw theory, to where does this urban legend trace its origins? It's hard to say definitively, but there are a few possible explanations. It is a possibility that the myth originated with dog fighters themselves. Men involved in this type of operation may have boasted of the powerful jaw strength of their champion fighters and even used the terminology that led to the eventual use of the term "locking jaw" as we know it today. A dogfighter may have gleefully reported that his dog "locked onto" another dog, and through repetition, misunderstanding, and misuse, "locking jaw" became the new phrase. This may well have been a point of pride for the owners of these dogs though there isn't even an ounce of truth to the phenomenon. 

Another theory suggests that this term is derived from the earlier practice of "bull baiting." Bull baiting was encouraged in breeds such as Bull Terriers, American Staffordshire Terriers, and other "game" dogs. Its sole purpose was the sport, and it was bloody, harmful to the bulls, and cruel. The most successful bull baiting dogs possessed the singular focus to bite down on their opponent and refuse to release the bite until their opponent submitted or died. This was not due to any locking ability but rather to the tenaciousness of the dog. The dog fighter valued the dog's stubbornness highly. This quality earned him lots of money!

Other Solutions and Considerations

On the opposite hand, "lockjaw" is a medical condition that can occur in dogs. It is essentially an infection after contamination by a bacteria known as Clostridium tetani. This illness can be contracted through dirt or other areas marked by low oxygen concentrations and transmitted through dead tissue from injuries. This advantageous bacteria enters the animal through the open wound site and begins to attack the nervous system. Dogs suffering from lockjaw will exhibit different symptoms including fever, lack of energy, painful urination, inability to defecate, pronounced stiffness of the muscles and extremities, and respiratory distress. Left untreated, lockjaw can lead to death. Lockjaw is a very serious disease. Should you suspect your dog is suffering from this, it is essential that you immediately take him to your veterinarian. There, your vet will conduct routine blood tests to determine if you dog carries the bacteria Clostridium tetani. 

Treatment is long term and requires hospitalization for a period of at least a month. If the disease is advanced at the time of diagnosis, your dog may be unable to eat without assistance and may require the insertion of a tube to ensure regular feeding. Dogs suffering from lockjaw become deeply affected by light, noise, and even touch and must be kept quiet and sedated during their recovery period. Asphyxiation is another concern. Your vet will carefully observe your dog to make certain he is not experiencing breathing problems. A breathing tube can be inserted if necessary. As a final preventive measure, your dog will also be given medication to halt the toxin's affect on his system. Dogs can successfully recover from lockjaw if the disease is detected and treated in time. The road back to health is arduous and will require your consistent monitoring and involvement.


Though we have all heard the locking jaw theory, there is not any substance to it. The rumor mill has led many people to believe this phenomenon is true and condemned dogs that have no genetic abnormalities that set them apart from any other. Without hard scientific evidence to support the idea of a "locking jaw," all we can do is dismiss it.

Written by a Parson Russel Terrier lover Jason Homan

Veterinary reviewed by:

Published: 03/15/2018, edited: 01/30/2020

What do you think?

Wag! Specialist
Need to upgrade your pet's leash?

Learn more in the Wag! app

Five starsFive starsFive starsFive starsFive stars

43k+ reviews


© 2024 Wag Labs, Inc. All rights reserved.

© 2024 Wag Labs, Inc. All rights reserved.