8 Common Causes of Aggression in Dogs

small pomeranian puppy sitting on a couch and barking

There are a lot of dog breeds that get a bad reputation. And, sometimes the breed is assumed to be one of the causes of aggression in dogs, which isn’t accurate. Big, physically imposing breeds that look intimidating often get a bad reputation as “dangerous” or “aggressive”. But, some small dog breeds bite just as often and more often in some cases. Plus, they often go underreported while bites from larger breeds are reported more often, which only contributes more to misinformation about “dangerous breeds”.

But, are there really dangerous dog breeds?


There are certain traits and characteristics that can become aggression if a dog is abused, not properly socialized, is untrained, or is trained to be aggressive. However, all of this has to do with how a dog is raised and not their breed. Plus, there are other situations and factors that can cause a dog to bite. Understanding the causes of aggression in dogs can go a long way in understanding dog behavior, knowing what to look for as warning signs, and preventing dog bites.

What Dogs are Dangerous?

No dog breed is inherently dangerous. But, dogs are often what you make of them, which is why the saying exists that “there are no bad dogs, only bad owners”. Any dog can become dangerous or aggressive if they are not properly socialized or trained or if they are specifically trained to be aggressive. Abuse is a tragic situation and although abuse can trigger aggression in dogs, that’s not always the case.

Also, some of the ways dogs communicate are considered to be aggressive. For example, growling, barking, nipping, snapping, and biting are all considered aggressive behavior in dogs. There are several situations and reasons why a dog might be exhibiting aggressive behavior. Some of it is related to how they were raised, some of it is part of normal dog communication, and some of it is completely situational. Knowing the causes of aggression in dogs can help you figure out what is going on when a dog is displaying aggressive behavior.

8 Common Causes of Aggression in Dogs

Growling, snapping, biting, and more are all acts of aggression in dogs and may be displayed situationally by any dog. Some may display them more or less often depending on how they were raised, trained, socialized, and more.

Knowing what is causing the aggression in a dog can help you correct the behavior either by yourself or with the help of a professional dog trainer. Here are some common causes of aggression in dogs:

1. They Have Been Trained to React Aggressively

In general, dogs repeat behaviors that are consistently rewarded. Attention, even if it is considered negative by a human, sometimes still counts as a reward for a dog. A dog may react aggressively simply because they have been intentionally or accidentally trained into it.

Intentionally Trained to Be Aggressive

Dog owners who wish to have a protector and guard dog may actively train their dog to react with aggression towards strangers on their property. This is a poor decision and an owner who does this should not own a dog – period. If you are in danger, a dog will often protect you naturally because you are their human – they don’t need to be trained into it.

The exceptions to this are military and police dogs who are trained by professionals to be aggressive in specific situations as their job. Outside of these specific situations and outside of the job, these dogs do not tend to be aggressive. Also, they are often only aggressive when given a specific command by their handler. This type of training should not be applied to a family pet and certainly not attempted by anyone other than a trained professional.

Accidentally Trained to Be Aggressive

Dogs often take their cues about how to react to a situation from their owners. This is especially true when they are young, experiencing new situations, and learning about the world.

An owner who reacts fearfully or is suspicious of strangers or new situations will often “accidentally” train their dog to react the same way. Or, they won’t correct or re-train aggressive behavior when it happens in the first place. This often results in a poorly trained and poorly socialized dog who approaches new people, animals, and situations with suspicion and fear. These dogs may react with fear-based aggression in these situations, which can lead to bites.

It’s also common for owners to accidentally train their dogs into certain behaviors as puppies that are undesirable once they are fully-grown adults. Because dogs repeat rewarded behaviors, it’s important to remember that what may be cute as a puppy may not be cute as an adult dog.

A puppy that is allowed to mouth on your hand or nip at fingers during playtime could grow into a dog that bites or nips at hands as an adult. Similarly, a small dog breed or puppy that is encouraged to growl, bark, and snap because “it’s cute” or funny when they are small can easily grow into an aggressive small dog or a larger adult dog that is prone to aggression.

2. The Dog Has Not Been Socialized Properly

Socialization is important to any dog breed and is particularly important early on in your puppy’s life. A properly socialized dog approaches new situations and people with confidence and curiosity – not fear. Dogs that have been well-socialized have healthier psychological growth, better coping skills, and tend to exhibit healthier behaviors overall. There are many ways to socialize a puppy and enrolling in puppy training classes is one of them.

On the other hand, poorly socialized dogs tend to approach new situations and people with anxiety and fear, which often leads to aggressive behavior. After all, if something feels like a threat to your dog, they will react accordingly. For them, this could simply be fearful behavior. For other dogs, it could be aggressive behavior.

Protective Instincts

This is also why socialization is especially important for dog breeds with protective instincts. A dog breed that is naturally protective that is also poorly socialized can view things as a threat that shouldn’t be viewed as a threat and react aggressively.

They can also become extremely territorial and become hyper-vigilant over whatever they perceive as their territory. But, if that same dog were properly socialized, they might retain a watchful eye or have a healthy wariness for any signs of a threat, would only view actual threats as threats, and would not react aggressively to non-threat situations.

3. They Are Afraid or Anxious

One of the common causes of aggression in dogs is fear or anxiety. Usually, fear-based aggression only occurs when a dog feels in danger or when they need to defend themselves. This is why socialization and training early and often are important.

A dog that is not well-socialized or trained often feels in danger with everything. In these cases, they may react with aggression because they feel like they need to defend themselves because they are viewing things that aren’t actually threats as threats.

The same is true for a dog that is anxious. In their anxiety, they may view situations, people, or things as a threat and react aggressively. They may also lash out by growling, snapping, or biting because they are overwhelmed by their anxiety and don’t know how to react.

Anxious dogs can sometimes appear as shy dogs. Starting socialization as early as possible is best, and there are tips to help your shy dog interact with other dogs and people. Depending on the severity of their shyness or anxiety, you may want to get the help of a professional dog trainer that specializes in socialization.

4. The Dog is Guarding Resources

Dogs may exhibit aggressive behavior when they are guarding resources. When dogs are exhibiting resource guarding behavior, they are aggressively possessive of what they cherish the most such as food, a treat, their bed, their favorite toy, their favorite human, etc.

They may snap or growl at any person, another dog, or another animal that comes near their resource. If left unchecked, they may escalate to bites, full-out fighting, and more severe physical attacks.

5. They May Be Displaying Social Aggression

Social aggression refers to the growling and snapping that occurs within the established hierarchy in a pack system. With multiple dogs in the family, they will work to establish a pack hierarchy for who gets a certain napping spot, toy, etc.

In some families, the pack hierarchy will shift. And, when shifting occurs or the current “Alpha” of the dogs feels one of the lower members is messing with the order of things, they may try to correct them with a snap or a growl.

Mother dogs will also use growls, nips, and snaps to teach their puppies manners. Older dogs will often do the same with younger dogs. Dogs will also often display these behaviors to establish and assert boundaries with other dogs, other animals, and even their humans.

If these initial warnings are ignored, social aggression can sometimes move from growling, snapping, or nipping to actual biting or fighting. So, it’s important to pay attention to what signals your dog may giving you or others.

6. The Dog Could Be Feeling Too Restrained By Their Leash

Leash aggression refers to aggressive behavior that a dog displays when they are on their leash, especially when the dog is well-socialized, friendly, and approachable when they are not on their leash. If your dog starts barking, snapping, or lunging at everything as soon as their leash is on when they don’t usually act that way, they could be what is considered “leash-aggressive”.

Usually, this is caused by your dog feeling too restrained by their leash and results in these aggressive behaviors being directed at other dogs while they remain leashed. A bite in this instance, at least from your dog, is rare, but it can happen. First, you want to visit the vet to rule out any underlying medical cause and then you want to enlist the help of a professional dog trainer to help fix the behavior.

7. They Could Be Frustrated

When a dog is not able to get to something, they may become frustrated and take out that frustration on someone or something else. This is called redirect aggression and can be a result of poor training or poorly enforced boundaries, but that isn’t always the case.

Another type of aggression related to frustration is when a usually well-mannered dog reacts snaps or bites as a last resort or in response to some sort of teasing. This is common in families with children who do not teach their children how to properly interact with their dog or don’t enforce boundaries between their children and their dog.

Children, or adults, who push your dog around, pull on their ears or tail, stick their fingers in your dog’s mouth when they’re trying to eat, crawl all over the dog, force your dog to interact with them despite the dog’s attempts to get away, etc. are all causing your dog distress and frustration.

Oftentimes, the dog has growled, barked, or snapped multiple times as a warning. Then, when these warnings have been ignored and the behavior continues, the dog lashes out as a last resort to protect themselves. Understanding dog body language, teaching everyone how to properly interact with a dog, and respecting your dog’s boundaries can help prevent this type of aggression.

8. The Dog Could Be Sick

A dog could lash out when they are in pain or when they are sick. Avoiding contact with you or acting aggressively is sometimes one of the signs your dog is in pain. If they aren’t feeling well, they may growl or snap at you if you won’t leave them alone.

There are also some serious medical ailments, like brain tumors, thyroid disorders, neurological issues, and seizures, that can turn a sweet, friendly dog into an aggressive one. This is why it’s important to visit the vet if your normally friendly dog is suddenly acting aggressively without reason.

These are a few of the most common causes of aggression in dogs that you can use to better care for your dog and understand the reasons behind their behavior. This is also valuable insight that can hep you develop the right strategies to help calm a reactive dog. Understanding what is triggering your dog’s behavior can help you correct things through training, protect your dog, and prevent bites or fights.