Expert weighs in on sudden aggression causes

By Dr. Beth Leermakers

Dog fights are stressful and scary — especially when they seem to come out of the blue. What is going on when your dog, who has never displayed aggression, suddenly attacks his canine buddy? And what can you do to prevent future scuffles?

If you suspect that an injury, arthritis or an illness may be causing aggressive behavior, head for your vet clinic.
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As the caregiver for several large dogs (including foster dogs with unknown histories), I have some experience keeping the peace. When I have an anxious or seemingly aggressive foster dog, I call in canine behavior specialist Tiffany Baker, CBCC-KA, CCUI, LFDM-T, owner of Boss Babe Dog Training ( All those initials after her name mean that Baker is certified and well qualified to handle anxious and aggressive dogs. Baker graciously shared resources and recommendations and reviewed this article for accuracy.

What is aggression? The American Kennel Club defines aggression as “hostile, injurious or destructive behavior” toward a person or another animal. Several behaviors can lead to (or look like) aggression:

Reactivity. Reactivity is often confused with aggression. Reactive dogs overreact to certain stimuli or situations — such as bicycles, moving cars, small children or feeling trapped on a leash — that frighten them. Reactive dogs need distance from the feared object to feel safe, so you need to give them space. Baker and I worked with Brodie, my former foster dog, to reduce his reactivity toward cars, bicycles, joggers and other scary, fast-moving vehicles we encountered on our walks. 

Fear. Fear is the most common cause of aggression. When dogs feel threatened, they run away from the feared object. When they are confined and can’t flee, they may fight to protect themselves. Fearful dogs may not give any warnings, other than body language, that a bite is coming. Learning to read body language is important, and you should NOT punish a dog for growling. 

Growling is a dog’s way of telling you to back off. It’s a warning sign that the dog is afraid or unhappy about something. If you don’t heed that warning, the dog may bite. 

Resource guarding. Dogs tend to guard items — food, treats, toys, beds and even people — that are valuable to them. Dogs may growl at a person or dog that threatens their prized possessions. Dogs that guard their food need to be fed separately from other dogs. People should NOT touch the dog’s food bowl while she’s eating, and children should be taught not to take food (or toys) away from her. 

If your dog is guarding you (growling at other dogs that approach you while you’re sitting on the couch or bed together), you may need to banish all dogs from the couch (or bed) — at least for a while. 

Pain. Dogs that are experiencing pain or discomfort may anticipate interactions with even beloved humans or dog buddies to be uncomfortable and painful. If their painful condition makes moving uncomfortable, they may not just get up and walk away from uncomfortable situations. To protect themselves, they may respond defensively, growling or baring their teeth to say “back off” or “stop bugging me.” 

How to Evaluate and 

Manage Dog Aggression

Visit your veterinarian. If you suspect that an injury, arthritis or an illness may be causing aggressive behavior, head for your vet clinic. The vet will do bloodwork, perform diagnostic tests and ask you questions to identify what’s going on and determine whether pain or another medical condition may be a factor. Medication to manage the pain and/or reduce anxiety may be necessary. 

Separate the dogs. “When it comes to displays of aggression from our canine companions, management is the key to success and keeping everyone safe,” says Baker. “Management may look like separating the dogs by using baby gates or a closed door during mealtime to prevent resource guarding behavior. Other times it may look like crating the dog at night to prevent any aggressive displays due to pain or discomfort when resting. Oftentimes, having two layers of management is ideal; sometimes management fails, so it’s always a good idea to have a backup.” I (Beth) separate my new foster dogs from my other dogs by crating them in a spare bedroom, behind a closed door. If the dog manages to escape from the crate (as dogs with separation anxiety sometimes do), the door contains them.  

Condition your dog to wear a muzzle. Some dogs may need to be muzzled when they are in fearful situations. Leash reactive dogs may need to wear a muzzle in the veterinary clinic waiting room, where they’re in close proximity to other dogs and cats. Visit for recommendations for muzzles and tips about muzzle conditioning. There is no shame in putting a muzzle on your fearful dog. I muzzle my dog, who is terrified of new people, when we go to the vet. The vet, techs and I all feel more comfortable and relaxed knowing that my scared boy can’t hurt anybody. 

Protect yourself if you need to break up a dog fight. “If conflict arises between your dogs,  make sure you keep our hands away from the dogs’ mouths,” recommends Baker. “Instead, separate the dogs with verbal interruption, a blast from a can of compressed air, a bucket of water or water hose, or using household items like a cookie sheet to wedge between the dogs. If you must physically handle the dogs, hold the hind end and then move to a separate space.”

Give everyone a time out. “Dog fights are stressful for all involved, so be sure to allow your dogs (and yourself) time to decompress and breathe before attempting to have the dogs together again,” said Baker. 

Consult a canine behavior professional and/or veterinary behaviorist. If you are unsure of the cause of the behavior change or need assistance with modifying the behavior, get expert help. Choose a well-trained professional who uses positive reinforcement, not the old-school, less effective “show the dog you’re the alpha” approach. 

Check out the Boss Babe Dog Training Facebook page for dog training tips. You can reach Tiffany Baker via her website, or call 469-410-6643.