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Why Is My Dog Aggressive to Other Dogs?

Sophie Jackson is a dog lover and trainer living in the UK. She competes in agility and obedience with her four dogs.

Dog on dog aggression is a relatively common problem and can make life stressful

Dog on dog aggression is a relatively common problem and can make life stressful

What Makes a Dog Aggressive to Other Dogs?

It is a beautiful day at the park, and your dog is happily pottering about, chasing his ball or sniffing the bushes. All is calm until another dog appears, they approach your dog and suddenly the calm is destroyed. Your dog barks, snaps and growls at the intruder, or maybe it is the other way around and your dog is on the receiving end of canine aggression.

It might be all over in seconds, or it may escalate into a fight. In a worst-case scenario, one or both dogs might be hurt, along with the owners getting bitten while trying to intervene.

Whatever the outcome, a peaceful day ends on a stressful note and can leave you lacking confidence in taking your dog to the park again.

Unfortunately, cases of dog to dog aggression appear to be on the rise, and this can leave us wondering if it is safe to walk our dogs outside of our own homes. Canine fights may even occur within a home where there are multiple dogs, leaving owners distraught.

Understanding the triggers behind aggression and why some dogs seem to 'hate' other dogs is key to resolving the problem. While not all dog aggression can be prevented, training can solve a lot of issues and help you to have a more enjoyable time with your pet.

Canine interactions can be very subtle, what can start as a friendly sniff can suddenly develop into aggression

Canine interactions can be very subtle, what can start as a friendly sniff can suddenly develop into aggression

What Is Aggression?

In its simplest form, aggression could be defined as a negative reaction to another dog that causes the recipient to feel threatened or fearful.

However, aggression is far more complicated than that and some actions that people perceive as aggression can even be playful or appropriate canine interaction.

For instance, an older dog may snap at a puppy that is pushing its boundaries and cause the puppy to cry. This is the older dog telling the puppy to behave and as long as it is not excessive or results in injury to the puppy it is a completely normal part of canine behaviour.

Growling and lip-lifting are other canine behaviours that we term aggressive, but are used by our dogs to voice their displeasure at the behaviour of another canine. These early warning signs are designed to stop the unwanted behaviour of the other dog and a well-mannered individual will respect them and back off.

Dogs are entitled to tell another dog their behaviour is inappropriate in this fashion - it is correct canine communication, and the same as us telling someone we don't like what they are doing near us. Problems arise when we punish dogs for voicing their feelings, or when a dog ignores the warning signs it is being shown.

The other side of this scenario is the person who does not realise the behaviour their dog is displaying is aggressive and believes it is 'playful' or 'friendly'. They allow their dog to bully others and this can lead to dog fights.

Many signs of aggression are subtle, using body signals that another dog recognises, but a human may miss. If noticed, these early signs can predict the beginning of a dog fight. They include:

  • standing stiff-legged
  • staring at another dog
  • lifting the tail over the back
  • head back and raised
  • baring the teeth
  • growling
  • circling another dog
  • attempting to 'tower' over another dog by making themselves taller
  • forcing another dog into a corner
  • pinning a dog (often confused for play)
Some dogs prefer not to interact with other dogs, and that's ok

Some dogs prefer not to interact with other dogs, and that's ok

Types of Aggression

Aggression is sometimes fitted into boxes to represent the 'type' of aggression. While this is convenient when discussing aggression it has to be remembered that this is a complicated behavioural issue and there can be many layers to the problem.

  • Fear Aggression - possibly the most common cause for certain behaviours and a trigger behind other more specific types of aggression. Fear causes a dog to react fiercely towards another in an effort to prevent that dog from coming near to them.
  • Resource Guarding - this is when a dog feels the need to protect something it perceives as belonging to it. This could be a toy, food, their bed or a person. Resource guarding is complex and may only be triggered in certain situations or by certain dogs. Some breeds have a more natural tendency towards this behaviour. It can be linked to fear aggression, as the dog is afraid something it values is going to be removed from it.
  • Breed Aggression - this is when a dog has an aggressive tendency towards a specific breed, but is fine with all others. This often occurs when a dog has been frightened or even attacked by a particular breed and so learns that that breed represents a threat to them.
  • Protective Instincts - some dogs will become protective over either a person or another dog. This is not the same as resource guarding, the dog is not fearful the dog or person is going to be removed, but believes they are threatened by other dogs and so begins to protect them.
  • Overreaction to Bad Manners - this is sometimes known as 'being the fun police'. It is when a dog overreacts to another who is being too exuberant or playful. This is not the same as a dog who snaps or growls to tell another dog 'enough'. This is when a dog reacts to exuberance by attacking another dog. Some dogs develop this behaviour if they constantly meet over friendly dogs that do not respond to subtle warnings.
  • Bullying - While bullying is a human term and not precisely suitable for dogs, there are instances when a dog will try to throw its weight around with other dogs and this can become more aggressive over time. This may be due to the dog being allowed to rough house with others or wanting to resource guard.
  • Pain-based Aggression - this is a type of aggression often overlooked. Dogs are very stoic and can mask pain well until they are approached by a bouncing dog and fear they are going to be knocked over or jumped upon in a way that will hurt. A typical example is an older dog with sore joints, who lunges at other dogs it fears may hit into it.
  • Sexual Aggression - this can occur in males and females. Intact males may fight if they have caught the scent of a female in season. They will fight for the right to mate with her. Females may become aggressive when in season towards males because they are not ready to mate. Hormonal changes as a dog matures can lead to aggression towards dogs they previously tolerated.
  • Household Stress - Stress within a household affects our dogs too and can cause them to react aggressively and unexpectedly to other dogs. Noticeable times for this are holidays, when a dog's routine is disrupted and guests may be visiting.
  • Trauma - Occasionally, dogs who have suffered extreme trauma will be prone to aggression. This is usually seen in abuse cases, such as where a dog has been used for fighting.
  • Reaction to Illness - Some dogs struggle with illness in other dogs and will attack the sick dog out of fear. The illness within the dog makes the other anxious, or causes the sick dog's behaviour or smell to change which triggers an attack.
  • Neurological - while the majority of dogs exhibiting aggression will have a trigger that can be determined, a minority of dogs will exhibit unpredictable aggression. This is usually linked to a problem in the brain (brain tumour, epilepsy) which causes sudden outbursts of aggression. This has also been labelled 'rage syndrome'. It is very rare and dogs will usually exhibit other subtle signs of a problem.
Resource guarding around other dogs is a common trigger for aggression

Resource guarding around other dogs is a common trigger for aggression

Why You Cannot Punish Aggression

Dog to dog aggression needs an understanding of the situation when it occurs and the triggers involved. Since fear is often a key component to aggressive behaviour, it is important to realise that punishing a dog for being reactive is liable to worsen the behaviour.

Think of it this way: your dog is anxious around larger dogs because as a puppy it was knocked over in play by a bigger dog. This scared it and so now it wants to keep the big dogs away from itself. When a big dog approaches it lunges and barks to make it clear the dog should keep away. However, you, the owner, react to its behaviour by punishing the dog. This increases the dog's anxiety and makes it even more convinced big dogs are bad and need to be scared away.

Punishing reactive behaviour will usually have 1 of 3 outcomes.

  1. Increase the reactive behaviour
  2. Has no effect and the dog has the same issues all its life
  3. Suppresses the behaviour, but does not solve the problem

No.3 is the most dangerous outcome. The dog suppresses its reactivity out of fear of punishment, but the emotions behind its reactivity remain. The dog grows more and more stressed, and becomes a ticking timebomb. One day this dog may become so overwhelmed it lashes out at another dog resulting in severe injury to one or both of them.

Punishment takes many forms. It might involve striking the dog, forcing them to the ground on their side, or jerking them up with the lead. It may involve putting a deterrent collar on them, such as a shock, prong or spray collar. None of these methods will improve the situation, but can lead to the behaviour being suppressed to start that ticking timebomb. Dogs treated this way will not improve around other dogs and will remain a danger to others.

Milder punishments might be grabbing the dog's collar, saying 'no!' fiercely, or shouting at the dog. In the middle of a dog fight, such reactions are natural, but they do not help the problem. Shouting aggressively may even cause a dog to think you are 'joining in' with the behaviour and increase their reactivity.

There are also such things known as positive punishments. These place a consequence on the dog's negative behaviour. For instance, if a dog is protective over its toy around another dog, the toy may be removed. Or if a dog is sitting next to its owner and snarls at another dog, the owner may force the dog to move away from them.

While these may seem logical actions to us, to a dog they will only reinforce why they were aggressive in the first place.

For example, in the first scenario, the dog is resource guarding because it is worried it will lose its toy. By removing the toy, it is confirmed to the dog that there is a danger of losing it which causes them to be more anxious around their toy in the future. This has the potential to lead to further aggression.

In the second scenario, the dog is being protective of its owner and fears another dog taking its place. By removing the dog when it snaps, it is experiencing the thing it feared the most and once again increases its anxiety.

So, how do we help our dog without punishing it?

Some dogs may never be comfortable at the dog park, and will need to be walked somewhere quieter

Some dogs may never be comfortable at the dog park, and will need to be walked somewhere quieter

Reducing Aggression: What You Need to Know

Before attempting these methods to reduce your dog's aggression towards other dogs, it is first important to set a realistic goal for what you want to achieve with your dog. An ideal outcome would be a dog that can be around other dogs without any issue, but this may not be possible to achieve with all dogs, depending on how serious the problem is to begin with.

With any dog that has previously been reactive, it will be important to monitor any interactions it has with other dogs and to always be prepared for the behaviour to resurface. Some dogs can become tolerant of others, but will prefer not to mix with them. Be honest about your dog, and don't set yourself up for failure with unrealistic goals.

The first part of understanding your dog's aggression is to determine potential causes and triggers. If your dog was once attacked by another dog, this could trigger them to be defensive in the future, for instance.

Some breeds are more predisposed to being reactive to other dogs, and not all breeds play or interact the same way which can cause confusion and result in aggression.

You should ask yourself the following when considering your dog's aggression:

  • Did something occur that started this aggression (dog attack, rough play, or being chased by other dogs when a puppy)?
  • Is my dog anxious or underconfident?
  • Is there a pattern to the aggression (i.e. targeting certain breeds)?
  • Does my dog only react when other dogs get too close?
  • Are there certain environments where my dog is worse (i.e. at parks or when highly excited)?

If you have taken on a rescue dog, it is unlikely you will be able to answer all of these questions, but answer as many as you can.

Once we have these questions answered to give ourselves a better understanding of our dog, we want to act in three key areas to resolve the problem:

  1. Counter-condition the aggressive behaviour and reinforce positive behaviour
  2. Develop a strong relationship with our dog, including a sound recall
  3. Build general confidence and reduce stress or anxiety in our dog
Counter-Conditioning involves making positive associations instead of negative ones

Counter-Conditioning involves making positive associations instead of negative ones


Counter-conditioning is a hugely powerful training tool that works by changing negative associations to positive ones. This is how it works: When something that normally causes a dog to react aggressively appears, something positive occurs to change the association.

  • Unconditioned: Dog sees dog - reaction - barks, lunges, etc
  • Counter-conditioned: Dog sees dog - owner offers food/toy and starts playing with dog - reaction - dog associates another dog with fun with its owner

People think that giving a dog food or a toy when it is reacting to another dog is rewarding the aggression. It is not. It is offering a distraction and gradually associating seeing another dog with good things. Over time, instead of reacting to another dog, you will see your dog look to you instead, anticipating food or a toy.

The important part of counter-conditioning is understanding that to begin with it must be 100% consistent. That means every time a dog approaches your dog you offer them food or a game. This means being conscious of where you are walking, if you are likely to meet other dogs, and to be focused on your dog rather than distractions like your phone or grabbing a cup of coffee.

Over time, if you work with the other strategies listed as well, the need for counter-conditioning will diminish and you can start to reduce rewards.

For instance, instead of needing to reward whenever a dog comes into view, you only need to reward when the dog comes close.

Depending on the fear level of the dog and what its original trigger is behind the fear the length of time it takes for counter-conditioning to work will vary. It is a time-consuming process, but it has been shown to be one of the most effective methods for reducing fear-based reactions in dogs.

Teaching a dog to look at you instead of reacting to other dogs is a great game to reduce aggression

Teaching a dog to look at you instead of reacting to other dogs is a great game to reduce aggression


Desensitisation is the term given to reducing the power of something that causes a negative reaction in a dog. When used in conjunction with counter-conditioning, desensitisation enables a dog to learn how to respond better to situations and to reduce fear.

Desensitisation works by placing the dog far enough away from the thing that triggers a reaction (in this case, other dogs) and rewarding positive behaviour. This could be as simple as the dog looking at you rather than the other dogs, but can be advanced to asking for the dog to perform tricks or other behaviours. These behaviours should always be things the dog enjoys doing and should not place the dog in a vulnerable position (such as lying down). The behaviours should be rewarded to reinforce the good behaviour.

This links with counter-conditioning in that the dog is being conditioned to perform a new behaviour when another dog is present that is incompatible with the old behaviour.

One very useful game is to teach the dog that when it sees another dog it should focus all its attention on you instead of growling/lunging, etc. This is done by setting the dog up far enough away from other dogs that they do not spark a reaction and then pointing at the dogs or in some way having the dog look in their direction (you could say 'look' or 'what's that?'). You then praise the dog for looking without reacting and reward them.

As you progress the game, verbally praise your dog, but do not give the main reward until they look back at you. Next, ask the dog to 'look' and then wait to see what they do. Most dogs are smart enough to learn they have to look back at you to get the reward and you will find with time the dog will barely 'look' at another dog before it looks to you.

Keep building on this game and decreasing the distance between your dog and other dogs. At each stage we want success. If your dog reacts to another dog, you got too close too soon and need to back up.

Many people in the sports world use these types of games to teach their dog how to work around all sorts of distractions, so they can compete successfully.

Important things to bear in mind:

  • Make sure the dogs you are having your dog watch cannot approach you. You need them to be behind a fence, for instance, or have a friend walk their dog at a suitable distance. If you try this in a dog park then a dog could run over to yours and ruin all your work.
  • Work in short sessions - this is hard work for your dog mentally and should only be done for 5 or 10 minutes at a time, though you could do a few sessions during the day. Make sure your dog has a good break between sessions and has the chance to sleep.
  • Avoid interactions with other dogs. While you are desensitising your dog it is important you control their environment as much as possible and that means keeping your dog away from areas where loose dogs could run up to them. In an emergency, where you meet a dog unexpectedly, remember to revert to counter-conditioning to save the situation.
  • Keep your dog on a lead while you are working this stage, just in case they do react to another dog.
The stronger the bond you have with your dog, the more they will respond to you

The stronger the bond you have with your dog, the more they will respond to you

Building a Strong Bond

The better the bond you have with your dog, the more they will trust you and the more they will do as you say. This is because they will learn you are great to be with, you are reliable and consistent in your behaviour, and you can protect them from unwanted canine attention.

A strong bond means your dog will be more interested in working with you than what is going on around it, and, most importantly, it will create a strong recall which is going to be essential to manage dog aggression.

Building a bond is more than just having a dog that wants to sleep at your feet, it is about having a dog that is always eager to be at your side and ready to play with you. If you have started using the exercises listed above, you will already be creating a good bond with your dog, but there is lots more you can do.

Teaching tricks is a fun way to bond with your dog, as long as you teach them in a positive manner. This means not forcing the dog to perform something it does not want to, or manhandling it into a position. Clicker training is one way to teach tricks positively and there are lots of resources online for using it.

You can also focus on creating a great recall by playing games that involve your dog rushing to you for a reward. This could be playing hide and seek in the house, or having your dog run between you and another person to receive a reward. The more times you call your dog and reward them for coming, the more they will respond to a recall outside the house. Value for recall is often a weak area in peoples' training of their dogs, but is easy to remedy.

Just as important, when you are out on a walk have rewards with you. This means you can reward a behaviour you like instantly and continue to grow your bond. If you only offer rewards to your dog when at home, the dog will soon learn that when out on a walk coming to you gets them nothing - and, guess what? They stop coming!

A great recall is part of an amazing bond with your dog

A great recall is part of an amazing bond with your dog

Building Confidence in Our Dogs

Many dogs react aggressively towards others because they are under-confident and nervous of other dogs. This can happen for a variety of reasons, from the dog being attacked, to it being overwhelmed with dogs as a puppy.

An under-confident dog should not be simply left to get on with things at the dog park. They need to have their confidence built up gradually by meeting other dogs on an individual basis. These other dogs should be calm and laid back. If they ignore your dog, even better. Arranging special meetings does not mean the dogs have to interact. It may be enough for your dog to see the other dog across the street at first. The important thing is your dog should feel safe and secure during the meeting. During the meeting you should use counter-conditioning to make the experience positive. This is how we build confidence in our dogs.

As your dog grows in confidence, it may be possible to have them come closer to another dog. Some dogs have no interest in interacting with other dogs and that is perfectly fine. A dog does not need to want to play with another dog, or even sniff it. What is important is the dog can be in the presence of another dog without reacting fearfully.

Many dogs will never be comfortable in the dog park, because of the high pressure of social interactions, often with bouncy, high-energy dogs. If your dog is one of these, it is important to find places where you can walk them that are quieter and with limited interactions with other dogs. You may be able to rent an area for your dog to run off-lead in, or have access to beaches or forest walks. Even if you have to drive your dog to reach these areas, it is better than placing them in an environment where they feel stressed.

One thing to remember is that confidence needs to be constantly reinforced. Bad experiences may have a severe impact on your dog's confidence. These might include being attacked by another dog, or witnessing a dog attack. If something like this occurs, it is important to be aware it might cause your dog to be reactive again.

The good news is, the more you use the methods listed above, the stronger your bond will grow with your dog and the greater their confidence becomes. Even when bad things happen, it will be easier to work through them because you have already put in so much effort and time.

Be realistic about your expectations, not all dogs will progress to a stage where they can run with others

Be realistic about your expectations, not all dogs will progress to a stage where they can run with others

Using Medications to Reduce Stress

Stress can play a big factor in canine aggression. Stress can come in many forms. It may be a reaction to a situation at home. It could be the dog feels too much pressure at the dog park. It could be due to an illness in the dog, another dog in the house or even the owners. It could be because the dog is highly sensitive to noise or another trigger which means it is always on edge.

Often, we cannot immediately remove the stress that is affecting our dogs, because it is something out of our control. We may be able to reduce it by have a quiet place in the house our dog can go to, but in some situations stress needs to be medically managed.

There are a number of products on the market that are said to calm dogs. These include plug-ins and collars that release pheromones that are soothing to the dog. There are herbal remedies that can be sprinkled on food, sprayed on the dog's fur to create a calming aroma, or dropped in water or on the dog's tongue.

There are anecdotal stories about the success of these remedies, and many owners report seeing a change in their dog when using them.

Zylkene is the only over-the-counter remedy that is scientifically proven to reduce stress in dogs. It comes in a capsule form and contains an enzyme found in cow's milk. When given regularly it can reduce the stress levels of a pet.

All these remedies take time to get into the dog's system to have an effect.

Vets can also offer prescription remedies to assist a dog. These can have side effects and should only be opted for when other remedies have failed. Using stress medications strategically can help to place a dog in a calm frame of mind where they are better able to respond to training. However, it is important to bear in mind that if the drugs severely sedate a dog then it will not be learning anything from its training.

A walk with your dog should be a fun activity for both you and your dog

A walk with your dog should be a fun activity for both you and your dog

When Aggression Cannot Be Controlled

Though it is very rare, in some cases a dog's aggression will be impossible to counter-condition. The dog may react to the sight of a dog at any distance, and its reaction is always severe. It may be the dog suddenly lashes our savagely at another dog without warning, or bites its owner when it cannot attack a dog. Or it could be sudden severe aggression from a dog that never had an issue with other dogs before.

In such cases, there is sometimes a neurological (brain) issue at the heart of the matter. Neurological problems are something that is causing the brain to malfunction. It could be due to a brain tumour or a head injury that has caused brain damage. It could also be due to epilepsy. Certain medications may even cause temporary neurological changes.

Dogs can also be born with brain deformities, this might be due to the mother receiving inadequate nutrition during pregnancy, or could have a genetic factor.

When aggression is caused by neurological problems it is often impossible to correct. In some instances there may be medications that can assist, but in many cases the behaviour either needs to be managed or, if the dog becomes a serious danger to those around it, euthanasia has to be considered.

These cases are very rare and a dog usually will display other odd behaviours that indicate a neurological condition, such as obsessive behaviours, zoning out, or sudden personality changes.

Older dogs that suddenly develop a personality change may be suffering from a brain tumour or other condition that is impacting their behaviour. Again, it is not often possible for anything to be done to cure this issue and a dog's quality of life should always be considered first and foremost.

If you suspect a neurological issue with your dog, or want to rule it out before working on a training programme, you should contact your vet who may refer your to a specialist who can offer an MRI scan to see what is going on.

The quality of a dog's life must be considered first and foremost.

The quality of a dog's life must be considered first and foremost.

Resources for Aggression

Dog-to-dog aggression is very common and can range from mild cases to severe ones. The information provided in this article is intended as a guide and to apply to milder cases. For more serious cases it is always best to seek out professional, first-hand advice from a behaviourist. Animal behaviourists have a different skill set to dog trainers and should have a sound understanding of dog psychology.

When seeking professional help there are several factors to consider

  • The person should have qualifications from a recognised educational foundation
  • They should be registered with an organisation and uphold its rules
  • They should not encourage aversive training methods (these include shock collars, prong collars, choke chains, shaker or water bottles and punishing a dog)
  • Avoid anyone who uses the term 'dominance' to describe your dog's behaviour. The dominance theory has been wildly discredited and is not relevant to your dog's situation

Finding a suitable behaviourist can be difficult, but the following organisations have been set up to assist



This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

© 2021 Sophie Jackson