Why has my dog suddenly become aggressive?

Is it really sudden?

Although the behaviour may seem to have appeared out of the blue, there are usually signs that have gone unnoticed beforehand. For example, your dog may have been:

• Moving away from situations they found uncomfortable.

• Becoming quieter or more withdrawn (AKA behavioural inhibition).

• Showing more subtle signs of stress, such as avoidance, lip licking, yawning, becoming tense or turning their head away.

• Growling, snarling or showing their teeth.

• Becoming gradually less tolerant of handling or certain situations over time.

 

Dogs generally try to avoid conflict where possible and often communicate in subtle ways before resorting to more overt defensive behaviours. However, their earlier signs can easily be missed if we don't know what they mean, or if the dog’s communication is impaired by certain breed traits (e.g. thick fur, wrinkled faces, etc.).

 

 

Why might a dog's behaviour change?

Every dog is an individual, and behaviour is usually influenced by a combination of factors. However, some common reasons include:

 

1. Pain or illness

• Physical discomfort can have a profound effect on behaviour.

• Common behavioural presentations of pain in dogs include reduced tolerance of handling, being more easily startled, less sociable, more guarded over space or resources, more noise sensitive, less confident or quicker to react if they feel threatened.

• Pain is also rarely at a constant level all the time, which means dogs in pain can show unpredictable or inconsistent behaviour.

• This is why veterinary assessment forms a vital part of behavioural investigations.

 

2. Fear

• Fear is one of the most common emotional drivers behind aggressive behaviour.

• A dog may bark, lunge, growl or snap because they are trying to increase the distance between themselves and something/someone they find frightening or trying to stop an interaction that worries them.

 

3. Stress

• Just like people, dogs are affected by stress. Changes such as moving house, a new family member, visitors, building work, changes to routine, general unpredictability or ongoing exposure to worrying situations can reduce a dog's ability to cope.

• Sometimes it is not one stressful event, but many smaller stressors accumulating over time that contribute to behavioural change. This is commonly known as ‘trigger stacking’.

 

4. Frustration

• Some dogs become frustrated when they are unable to access something they want, such as another dog, a person, an object or activity. Some dogs may also get frustrated if their expectations of an encounter or situation are not met.

• Just like people, frustrated dogs may become uncharacteristically vocal or aggressive.

• Some dogs are more prone to frustration than others, and adolescent dogs often have much lower tolerance of frustration than older adults.

 

5. Learning

• If dogs have tried less overt forms of communication, such as changes in body language, avoidance or appeasement, and this has not worked to reduce the perceived threat, they may learn to escalate their communication over time.

• This can cause dogs to skip more subtle signs and go straight to aggressive forms of communication.

 

 

What should you do if your dog becomes aggressive?

If your dog's behaviour changes suddenly, the first priority is safety. Avoid putting your dog into situations where they are likely to feel stressed while you investigate the cause. The second priority is booking in a vet check so any underlying medical causes can be investigated and addressed. The third priority is contacting a behaviourist to help identify the causes and provide a plan to resolve these over time. 

 

 

What should you avoid?

It can be tempting to tell a dog off for growling or snapping. However, punishment rarely changes the emotion behind the behaviour, and in some cases can worsen it. For example, if a dog growls because they are frightened, punishing the growl does not make them feel safer. Instead, it may teach them that warning signals are ineffective, increasing the risk that they skip the growl altogether next time and go straight to a bite. Additionally, the use of punishment has been associated with increased risk of aggression in dogs, increased problematic behaviours, and damage to the dog-human relationship.

 

 

When should I seek professional help?

If your dog has shown signs of aggression or reactivity, or if their behaviour has changed or become problematic in any way, it's best to seek advice sooner rather than later. Early intervention can often prevent problems from becoming more established. As a CCAB-accredited Clinical Animal Behaviourist, I carry out comprehensive behavioural assessments that consider your dog's behaviour alongside their physical health, environment, learning history and emotional wellbeing and develop a behaviour modification plan tailored to your dog. If you're concerned about a recent change in your dog's behaviour, please get in touch.