Why Dogs Become Aggressive

Aggression in dogs is one of the most misunderstood behavior problems owners face. In this episode, Scott Sheaffer explains why dogs growl, bark, lunge, snap, or bite, and why these behaviors are usually not about a “bad dog.” Aggression is often communication, and the real issue may involve fear, anxiety, pain, resource guarding, frustration, genetics, early development, or learned behavior.

Scott also explains the difference between reactivity and aggression, why many dogs give warning signs before escalating, and why punishing those warnings can make a dog less safe rather than more reliable. This episode gives dog owners a clearer, more useful way to understand aggressive behavior and why identifying the cause matters more than simply trying to stop the behavior.

Episode Link(s):

Understanding Dog Body Language Video

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Disclaimer
This podcast is for educational purposes only and is not a substitute for professional advice. If your dog is displaying aggression toward humans, consult an experienced and knowledgeable canine behavior professional who uses humane, non-aversive methods, and always take precautions to keep others safe.

Scott Sheaffer and USA Dog Behavior, LLC, are not responsible for any outcomes resulting from the use or interpretation of the information shared in this podcast.

Transcript

After working with thousands of dogs and their owners, I’ve learned this: most aggression isn’t about a dog being “bad”. It’s about a dog trying to solve a problem the only way it knows how.

Today, we’re talking about one of the most misunderstood subjects in the dog world: aggression.

Why do some dogs become aggressive?

And more importantly, what is aggression actually telling us?

Aggression is one of those words that instantly raises the temperature in the room. If someone says, “My dog is aggressive,” most people immediately picture danger. They picture a bad dog. A dangerous dog. A dog who wants to hurt someone. And there is a degree of truth in all of those feelings.

But that’s usually not the right starting point.

Aggression is not a personality type. Aggression is behavior. And behavior has function – just like it does with humans. If you think about it, we do certain behaviors as people because we think it will achieve some kind of outcome. Dogs do the same thing with aggression.

This means the dog is trying to accomplish something with its aggression.

The dog may be trying to create distance. The dog may be trying to guard its food, a resting place, a toy, or a person. The dog may be trying to stop being touched in a way that hurts. The dog may be trapped, overwhelmed, frustrated, or afraid.

So the first question should not be, “How do I stop this?”

The first question should be, “Why does this dog feel the need to use aggression?”

That question changes everything. What’s causing the aggression?

Let’s start with something many owners find surprising.

A lot of aggression is defensive, even when it looks offensive.

A dog who barks, lunges, growls, snaps, or charges may look bold. He may look like he is trying to start a fight. But very often, that dog is trying to prevent one from starting in the first place.

I remember as a kid being bullied by a guy in junior high that was at least a foot taller than me. In the heat of the moment, I acted like I was the toughest guy in the world and wasn’t the least bit afraid of him. Truth is I was terrified and the LAST thing I wanted was a scrap with him. But he bought my little act, known as offensive defense, and he left me alone.

Dogs do exactly the same thing. 

When they are scared, they just want the scary encounter to end. They use aggression in the moment, to say, “Stop!”

Now, this doesn’t mean the behavior is acceptable. It doesn’t mean it should be ignored. It doesn’t mean there is no risk.

But it does mean we need to understand the emotional engine underneath the aggressive behavior. What’s causing it?

And here’s the number one reason you always need to address aggression in dogs.

If a dog barks and lunges at a stranger, and the stranger moves away, the dog learns something. That dog learns, “When I do that big scary display, the scary thing leaves. I feel better.”

From the dog’s point of view, it worked.

And behavior that works tends to repeat. It’s called reinforcement. The behavior literally reinforces the behavior. 

That’s one reason aggression can grow stronger over time. The dog is not necessarily becoming meaner. The dog is becoming more practiced at a strategy that has produced results. He is becoming quite proficient at making himself feel safe in the moment.

This is where we need to talk about reactivity.

Reactivity and aggression are related, but they are not exactly the same thing. The term reactivity is used incorrectly in the dog training world so much today that it has become an almost useless term anymore unfortunately.

Reactivity means the dog is overreacting to something in the environment. That overreaction might look like barking, lunging, whining, jumping, freezing, hiding, pulling away, or trying to escape. That list includes some aggressive behaviors and also some that are submissive. Reactivity is simply the term used for all the possible exaggerated and over-the-top responses a dog may have to a trigger – whether aggressive or submissive.

Aggression is but one possible expression of reactivity.

A reactive dog is not always an aggressive dog – reactivity can be shown using more submissive behaviors as I noted earlier. Here’s a good way to think of it, all aggressive dogs are reactive, but not all reactive dogs are aggressive. 

Reactive dogs are simply dogs that have exaggerated responses to triggers, such as to strangers in their home. These responses include behaviors that generally fall into 3 major groups: 1) fighting behaviors – aggression for example, 2) flight behaviors – trying to run away or 3) freezing -  just standing still, hoping to not be noticed.

And reactive dogs that are aggressive may only show aggression in very specific contexts or situations.

That distinction matters. Dogs that are aggressive show this aggression in very specific contexts and with specific triggers. Much of the general public thinks that an aggressive dog is simply just an “aggressive dog.”

Not true!

Good behavior work starts with accurate observations about what is triggering the dog’s aggression.

What exactly happened? Who was there? How close was the trigger? Was the dog on leash? Was food present? Was the dog resting? Was the dog touched? Was the dog startled? Was the dog in pain? Did the dog try to move away first?

Those details matter.

Let’s get more specific here. Why do dogs become aggressive?

Let’s walk through six of the most common reasons.

Number one reason that dogs become aggressive: fear and anxiety.

This is the biggest cause of aggressive behavior in dogs.

Only about 10% of fearful dogs simply run away from the thing that scares them. In fact, 90% of fearful dogs do the opposite. They bark, lunge, growl, snap, or bite because they believe that’s the best way to make the threat go away. And it frequently works for the dog.

And here’s the important part: the threat does not have to be objectively dangerous to us. The threat only needs to be perceived as dangerous by the dog. It doesn’t have to make sense to us. Think about it, do all of your fears objectively make sense? Probably not, but they’re real to you.

The stranger in your home may actually be friendly. The other dog may be harmless. The child may be well-intentioned. 

But if the dog feels unsafe, the dog’s behavior will be driven by that perception.

Dogs don’t react to reality exactly as it is. They react to reality as they perceive it.

That’s very important to remember and I stress this all the time with my private clients.

Number two reason that dogs become aggressive: pain and medical problems.

This one gets missed all the time.

Pain lowers tolerance. A dog with arthritis, dental pain, an ear infection, gastrointestinal discomfort, an injury, or neurological problems may become defensive when touched, moved, approached, or handled.

If a dog suddenly becomes aggressive, or if the behavior worsens without an obvious explanation, a vet exam should be part of the process.

This is especially true with older dogs.

Sometimes owners say, “He’s getting grumpy in his old age.”

Maybe. But maybe he hurts.

And if he hurts, behavior modification won’t correct the real issue.

Number three reason dogs become aggressive: resource guarding.

Resource guarding happens when a dog protects something valuable. Something valuable to the dog that is.

That might be food, a bone, a toy, a bed, a crate, a stolen sock or tissue, a doorway, a couch, or even a person.

The dog’s thought process is not complicated. “I have something important, and I am worried I may lose it.”

The mistake many owners make is trying to prove they can take things away.

They repeatedly reach for the bowl. They take the bone. They challenge the dog. They punish the growl.

That often makes the guarding worse because it confirms the dog’s concern.

From the dog’s perspective they learn: “I knew it. When people come near my stuff, they take it.”

A better approach is to change the dog’s emotional response. Teach the dog that human approach predicts something good, not loss, pressure, or conflict.

Let me take a second to tell you about a service I offer—when I come back, we’ll pick back up with the number 4 reason dogs become aggressive.

Alright—let's get back to it. 

The Number four reason dogs become aggressive: frustration.

Frustration can turn into aggression very quickly.

This is especially common on leash or behind barriers.

A dog sees another dog across the street. He wants to get to that dog. Maybe he wants to investigate. Maybe he wants to chase. Maybe he is conflicted. Maybe he is both excited and worried.

But the leash stops him.

The frustration builds. The body gets tight. The barking starts. Then the lunging starts. The behavior escalates quickly.

The leash didn’t necessarily create the underlying issue, but it can amplify it.

This is why leash reactivity when walking your dog can look so intense.

And it is also why simply tightening the leash, repeating commands, or trying to physically control every movement often makes the whole situation worse.

Number five reason dogs become aggressive: genetics and early development.

Some dogs are born with a more sensitive nervous system. Just like with people.

Some dogs are more easily startled. Some recover slowly from stress. Some are naturally more suspicious. Some have stronger guarding tendencies. Some have been bred for traits that can show up in challenging ways in a modern household.

Early development also matters.

The first few months of life are important. Puppies who do not get appropriate exposure to people, dogs, surfaces, sounds, handling, and normal life experiences may be more likely to respond fearfully later.

This does not mean the dog is doomed.

But it does mean we need to be honest.

Not every dog starts from the same place.

Some dogs need more structure, more distance, more careful exposure, and more thoughtful behavior work than others.

Number six reason dogs become aggressive: learning history.

Dogs repeat behavior that works.

If growling makes a person back up, the dog may growl again.

If snapping stops nail trimming, snapping may become more likely.

If lunging makes another dog leave, lunging may become part of the dog’s strategy.

This is not manipulation. This is learning.

And it’s one of the reasons aggression should be addressed early.

The longer a dog rehearses aggressive behavior, the more fluent that behavior can become.

That doesn’t mean the case is hopeless. But it does mean it can be more challenging when the behavior has been rehearsed over a long period of time.

It’s important to address aggression in dogs as early as possible for this reason.

Now, let’s talk about warning signs.

Most dogs don’t bite out of nowhere.

I know it can feel that way to the owner. But in most cases before a dog bites, the dog gives signals that were missed, misunderstood, or even punished.

Those signs may include turning the head away, lip licking, yawning, whale eye, freezing, stiffening, pinned ears, a closed mouth, hard staring, growling, or sudden stillness.

And growling deserves special attention.

Growling is not the problem.

Growling is information.

A growl is a warning. It is the dog saying, “I am uncomfortable. Something needs to change.”

If we punish the growl but don’t change the underlying emotion, we may create a more dangerous dog.

Why?

Because now the dog may still feel threatened, but he has learned not to warn.

That isn’t improvement. That’s suppression.

And suppression can be risky. And when dogs suppress warning behaviors, it’s called masking. If masking behavior is a deeply learned behavior in a dog, it can turn into them biting seemingly out of nowhere.

So what should owners do if they have an aggressive dog?

First, stop thinking of aggression as an obedience problem.

Yes, training may be a small part of the answer. But aggression is not ever addressed by simply teaching sit, stay, leave it, or heel.

Those skills may help with management, but they don’t automatically change the dog’s emotional response to triggers.

Second, identify the pattern.

When does the aggression happen? Around whom? At what distance? In what location? On leash or off leash? Around food? Around resting areas? During handling? When visitors enter? When another dog approaches?

Patterns tell us what the dog is trying to accomplish.

Third, manage the environment.

If the dog bites over bones, stop giving bones in high-traffic areas. If the dog lunges at dogs on narrow sidewalks, stop forcing close sidewalk passes. If the dog is unsafe with visitors, don’t allow visitors to walk in and interact freely.

Management prevents rehearsal.

And preventing rehearsal is a major part of changing behavior.

Fourth, learn body language.

Owners often wait for barking, lunging, snapping, or biting before they realize the dog is struggling. By then, the dog is already far along emotionally.

The goal is to see the smaller signs earlier.

A dog who stiffens, freezes, looks away, closes his mouth, or scans the environment may already be telling you he is uncomfortable.

I have a free 49 minute video on my website, USADogBehavior.com, which is a crash course on canine body language. You can easily find it on my website and I’ll put a link to it in the description for this episode.

Fifth, avoid punishment-based reactions that increase fear or suppress warning signs.

If aggression is rooted in fear, anxiety, pain, or conflict, adding intimidation may make the dog look quieter in the moment, but it doesn’t make the dog safer.

In most cases, it ultimately makes the dog more likely to resort to aggression.

And sixth, get qualified help early.

Aggression is not something to experiment with casually. The stakes are too high. A competent, experienced and rewards based behavior professional will look at the pattern, the triggers, the dog’s history, the environment, the owner’s handling, possible medical factors, and the safety picture.

That’s very different from just teaching commands. Unfortunately, there aren’t a lot of dog professionals who really understand this behavior and how to treat it. 

Let me repeat what you’re looking for in a dog pro to help you, a competent, experienced and rewards based behavior professional. I want experience to be the most important criteria in finding someone. Using positive reward based methods is also a very important criteria as well.

Here are the takeaways in today’s podcast.

Aggression is serious, but it is not mysterious.

Dogs become aggressive for different reasons.

Those reasons include: Fear. Anxiety. Pain. Frustration. Guarding. Genetics. Early development. Learning history.

When we understand the reason, we can correctly address the behavior.

By knowing these things, we can stop accidentally making the behavior worse. We can help the dog feel safer. And in many cases, we can teach the dog better and alternative ways to navigate the world.

Aggression is communication from your dog, and the message matters more than the noise. When we look beyond the bark, growl, lunge, or snap, we can begin to see what the dog is actually struggling with. That is where real behavior change begins.

Now, you understand the real story behind your dog’s behavior.