Dog Reactivity - Not Just a Training Issue

Featuring Nikki Warner from Reservoir Dogs, Cardiff

Many trainers, myself and Nikki included, are seeing more and more dogs labelled as reactive. It’s stressful for owners, it’s stressful for dogs, and it can feel like the behaviour comes out of nowhere. But before we can help these dogs, we need to understand what reactivity actually is.

What Do We Mean by Reactivy?

When owners describe their dog as reactive, they’re usually talking about big, intense, seemingly out‑of‑control responses to something in the environment. This might be:

• other dogs

• people

• traffic

• noises

• things passing the window

• sudden movement

• or even unfamiliar objects

  
  

To the owner, it can look like the dog has  ‘lost their mind' - barking, lunging, spinning or pulling, and it often feels like nothing you do makes a difference.

But reactivity isn’t always loud. Some dogs freeze, hide, or shut down. These are still reactions — just quieter ones.

Why Does Reactivity Happen?

Reactivity is not a dog being naughty or difficult.  It’s a dog who has reached the edge of their ability to cope. There are many reasons this can happen:

• Fear

• Frustration

• Genetics

• Pain or discomfort

• Breed‑specific behaviours

• Learning history (e.g., barking makes scary things go away)

• Lack of choice to move away from things

  
  

Often, dogs learn that reacting works. If a dog barks and lunges and the trigger moves away, the dog gets space,  and space feels safe.

Living Close to the Edge: Micro‑Stressors Add Up

Our world is fast, noisy, and unpredictable. Dogs experience countless micro‑stressors throughout the day — sounds, movement, smells, interactions, changes in routine. If a dog struggles with multiple things in their environment (for example, noises and dogs and traffic), they may be living close to their stress threshold most of the time.

When a dog is already near their limit, it takes very little to push them over it.

The Impact of Early Experiences

If a dog has gone through puppyhood and adolescence feeling worried or overwhelmed, reactivity can become deeply ingrained. Experiences during these developmental periods have lifelong behavioural consequences.

Each time a dog encounters something scary, the body releases stress chemicals through the HPA axis. If this happens repeatedly,  especially during sensitive stages,  this can change the brain's architecture and how a dog perceives the world. The nervous system stays on high alert, and reactions become quicker and more intense.

The adolescent brain is also busy wiring in ‘important’ behaviours. If reacting has been the dog’s go‑to coping strategy, the brain takes note and strengthens those pathways.

How Did Your Dog End Up Being Reactive?

There are so many things that can cause a dog to become reactive, including: 

• Genetics (some breeders breed from anxious parents which is never a good idea as this will in some wat be passed on to the puppies)

• Traumatic or scary early experiences ( including before 8 weeks old)  

• Lack of positive early experiences  

• Underlying pain or discomfort that often goes unnoticed

• Repeatedly being exposed to the situations that cause them to react, strengthing the behaviours like lunging, barking and snapping.

We will likely never know the exact cause.

Pain: The Hidden Driver of Reactivity

Undiagnosed pain is likely very common in reactive dogs. Pain activates many of the same pathways as stress and keeps the body in a state of fight‑or‑flight. A dog who is uncomfortable is closer to their limit, more irritable, and more likely to react.They are more likely to want to defend their bodies by keeping things away.

Pain can also create negative associations.For example: A loud noise startles the dog , they tense up,  it hurts, and next time, they’re ready to defend themselves as soon as they hear the noise or smell the things that predicts the scary thing is coming.

A dog rushes at your dog and it hurts - again, they are ready to protect themselves quicker next time by barking, lunging or snapping.

This is why veterinary involvement is essential when undiagnosed pain or discomfort is suspected. You can’t just train away pain.

Why Being on Lead Can Make Things Harder for Reactive Dogs

Dogs value safety, and safety comes from choice and predictability. Leads remove both. When a dog can’t move away from something scary, their options become limited:

• bark

• lunge

• growl

• snap

• hide

• freeze

These behaviours are not bad manners, they’re survival strategies.

Owners Often Miss the Early Signs

Most owners aren’t trained to spot the subtle signals dogs give long before they explode; lip licks, head turns, slowing down, increased breathing rate, pulling on the lead, scanning, tension, sniffing as a displacement behaviour and many others .When these early pleas for help go unnoticed, and the dog continues to feel trapped or uncomfortable, reactivity escalates.

So How Do We Help a Fearful Reactive Dog?

There is no quick fix — and that’s because we’re not just changing behaviour. We’re helping to repair a nervous system that may have been flooded with stress chemicals for months or years.

Chronic stress affects:

• emotional wellbeing

• behaviour

• sleep

• immunity

• gut health

The gut–brain connection is powerful. A healthy gut sends 'safe signals' to the brain; a stressed gut does the opposite.

The first steps are about stabilisation, not training:

• Protect your dog from their triggers (indoors and outdoors)

• Prioritise rest — multiple restorative naps every day

• Provide enrichment that calms rather than excites

• Support gut health with appropriate diet and biotics

• Reduce overall stress in the home and within daily routines

• Investigate pain or discomfort with your vet, physiotherapist or a pain vet 

• Consider behavioural medication if recommended, it can help rebalance the chemicals driving the reactions and create a window to allow your dog to learn news things about their triggers.

• Avoid using a trainer that will punish behaviour with slip leads, noisy discs or rattle cans, physical force, 'corrections', or any spray or shock driven collar.

  
  

Only when the dog feels safer and more regulated can we begin changing how they feel about their triggers.

Work With a Qualified, Ethical Dog Trainer or Behaviourist

Reactivity rooted in fear requires long‑term, welfare‑first support. A qualified professional will:

• help you understand your dog’s body language

• explain the science behind fear and reactivity in an accessible way

• create safe setups for learning

• build new, positive associations

• liaise with your vet

• support you emotionally through the process

Nikki from Reservoir Dogs in Cardiff has some wonderful insight and experiences to share on the toipc. Nikki is also a qualified Dynamic Dog Practicioner which means she is skilled in identifying signs of underlying discomfort in dogs by analysing how they move, how they walk, and how they behave. Nikki says:

While pain is mentioned as a contributing factor, it’s often still underestimated in practice.

What I tend to see when working with dogs is that we focus heavily on the behaviour itself, the barking, the lunging, the pulling, but we don’t always step back and ask what state the dog is in physically.

Pain and discomfort don’t just sit in the background; they actively change how a dog experiences the world.

There is a growing body of evidence to support this. Behavioural changes are often one of the earliest indicators of pain in dogs, sometimes showing up before any obvious physical signs such as limping or stiffness (Camps, Amat and Manteca, 2019; Malkani, Paramasivam and Wolfensohn, 2024). This means that by the time we see clear physical issues, the dog may have been coping with discomfort for some time.

From a physiological perspective, pain activates the same stress pathways as fear. The body releases stress hormones, the nervous system becomes more sensitive, and the threshold for reacting lowers. This means the dog is already closer to that edge before anything even happens in the environment. What this can look like is a dog who previously coped now reacting to things they once ignored or reacting quicker and with more intensity.

It’s also important to remember that puppies can experience pain too. So, whilst it might feel like “they’ve always done that”, if a behaviour seems exaggerated or out of proportion, it’s worth questioning whether something else could be going on.

Another layer to consider is that pain is not always obvious, even on veterinary examination. Clinical exams and imaging do not always line up with what the dog is actually experiencing (Landsberg, Hunthausen and Ackerman, 2023; Kwik et al., 2025). Dogs can still run, play, and do the things they love, even when they are in pain, which can make it easy to assume discomfort isn’t a factor.

I’ve seen this first-hand with my own dog. She has a history of hip dysplasia and arthritis, alongside periods of acid reflux. Over time, I started to notice a pattern, her reactivity towards other dogs would increase when she was clearly more uncomfortable, and her sleep would be affected too.

At one point, her reflux started happening more often. I adjusted feeding routines and food choices, but nothing really made a difference. It was only when her pain management was changed that things settled.

What stood out wasn’t just the physical change, but the behavioural one. As her discomfort reduced, so did her reactivity.

There is also evidence linking pain to changes in behaviour such as increased fear, sensitivity, and defensive responses, particularly where dogs are trying to protect themselves from further discomfort (Landsberg, Hunthausen and Ackerman, 2023; Mills et al., 2020).

It’s also worth thinking about what might be going on in the gut. Certain behaviours that are often labelled as “behavioural”, such as excessive licking or unusual repetitive behaviours, have been linked to underlying gut discomfort or digestive issues in a number of cases (Bécuwe-Bonnet et al., 2012; Mills et al., 2020). This reinforces the idea that what we see on the surface is not always the full picture.

When you’ve got a "reactive dog", especially where things have escalated or feel a bit inconsistent, it’s worth looking at what might be going on internally, not just what you’re seeing on the outside.

That might include looking at movement, posture, gait, and patterns over time, as well as working alongside a vet or other professionals to rule out or address discomfort.

Whilst training is important, if the dog is dealing with underlying pain, we are often trying to change behaviour in a system that is already under strain.

References

Bécuwe-Bonnet, V., Bélanger, M.-C., Frank, D., Parent, J. and Hélie, P. (2012) ‘Gastrointestinal disorders in dogs with excessive licking of surfaces’, Journal of Veterinary Behavior. Available at: https://doi.org/10.1016/j.jveb.2011.07.003

Camps, T., Amat, M. and Manteca, X. (2019) ‘A review of medical conditions and behavioral problems in dogs and cats’, Animals, 9(12), p. 1133. Available at: https://doi.org/10.3390/ani9121133

Kwik, J., De Keuster, T., Bosmans, T. and Mottet, J. (2025) ‘Detection of maladaptive pain in dogs referred for behavioral complaints’, Frontiers in Behavioral Neuroscience, 19. Available at: https://doi.org/10.3389/fnbeh.2025.1569351

Landsberg, G., Hunthausen, W. and Ackerman, L. (2023) Behavior Problems of the Dog and Cat. 4th edn. Saunders

Malkani, R., Paramasivam, S. and Wolfensohn, S. (2024) ‘How does chronic pain impact the lives of dogs’, Frontiers in Veterinary Science, 11. Available at: https://doi.org/10.3389/fvets.2024.1374858

Mills, D. S. et al. (2020) ‘Pain and problem behavior in cats and dogs’, Animals, 10(2), p. 318. Available at: https://doi.org/10.3390/ani10020318