What Does "Reactive" Actually Mean?

A reactive dog responds to normal, everyday things — other dogs, strangers, bicycles, loud noises — with abnormal intensity. The response is out of proportion to the situation.

Reactivity isn't a diagnosis. It's a description of what we see: barking, lunging, pulling, growling. It tells us that your dog is struggling — not yet why.

Think of it as emotional dysregulation. Your dog isn't choosing to misbehave. They're reacting because their emotional system is flooded, and their "thinking brain" has gone offline.

Once triggered, they become so preoccupied with whatever set them off that they can't hear you, can't respond to cues, and can't take treats — no matter how delicious.

Reactivity vs Aggression: What's the Difference?

This is a question I hear constantly, and the distinction matters.

Reactivity describes an emotional state — intense arousal, big feelings, an overloaded system.

Aggression describes behaviour with intent — actions aimed at causing harm or resolving conflict.

A reactive dog is expressing overwhelming emotion. An aggressive dog is taking deliberate action. A dog can be both reactive and aggressive — but they aren't synonyms. The outward behaviour can look similar — barking, lunging, snapping — but the underlying motivation is different.

Why This Matters

Reactivity is a high-risk state for aggression. When your dog is over threshold, their thinking brain shuts down and instinct takes over. A dog who starts with fearful barking can learn that escalating to snapping makes the scary thing go away — and a reactive pattern can morph into defensive aggression over time.

The relationship works like this: each time your dog reacts and the trigger retreats (the other dog walks past, the person moves away), your dog learns that their big display worked. Over months and years, the behaviour becomes more intense and more automatic. What started as fear can become a well-practised defensive strategy.

Reactivity isn't aggression. But unaddressed reactivity is a risk factor for it.

The Three Types of Reactivity

The same barking and lunging can stem from completely different emotional drivers. While these aren't formal diagnostic categories, this practical framework helps identify what's motivating your dog — which changes everything about how you approach it.

Fear-Based Reactivity (Distance Increasing)

The most common type. Your dog perceives the trigger as a genuine threat and wants it to go away. The goal is to increase distance — "Get that thing away from me!"

You'll often see defensive body language before the explosion: tucked tail, ears pinned back, weight shifted away from the trigger, whale eye (showing the whites of the eyes), or freezing. Then it escalates to barking and lunging in a desperate attempt to drive the threat away.

This commonly develops after a traumatic experience or from inadequate socialisation during puppyhood.

Frustration-Based Reactivity (Distance Decreasing)

Your dog desperately wants to get TO the trigger — to greet, play, or investigate — but the leash prevents it. The goal is to decrease distance — "Let me get to that!"

This is "barrier frustration." A friendly, social dog who's consistently denied the opportunity to greet people or other dogs can develop intense, frustrated outbursts. The pulling, barking, and lunging look aggressive, but they're not. They're the canine equivalent of a toddler having a meltdown because they can't have the toy they want.

Over-Arousal Reactivity

Pure excitement overload. Your dog is so amped up they physically can't contain themselves — jumping, spinning, mouthing, vocalising. There's no fear or frustration driving it, just an inability to regulate high energy and poor impulse control.

The Critical Point

Fear-based and frustration-based reactivity can look identical from the outside. The barking and lunging appear the same. But they require very different approaches — making a fearful dog feel safer versus teaching a frustrated dog impulse control. Getting this wrong can make things significantly worse.

What Causes Reactivity?

Reactivity rarely has a single cause. It's usually a combination of factors working together.

Genetics and Temperament

Some dogs are born with a more reactive nervous system. Research shows "reactivity to stimuli" is a heritable temperamental trait — meaning it runs in families. If your dog's parents were anxious or reactive, they may have inherited a predisposition to high arousal.

Certain breed groups may show higher rates of reactivity, particularly those selected for alertness and rapid response: herding breeds, guarding breeds, and some terrier and toy breeds. This doesn't mean these breeds will be reactive — just that the genetic predisposition can be higher.

Inadequate Socialisation

The critical period for socialisation is roughly 3-14 weeks of age. During this window, puppies build their mental "database" of what's normal and safe.

Dogs who miss positive exposure to varied people, dogs, sounds, and environments during this time are more likely to find unfamiliar things frightening as adults. Quality matters more than quantity — chaotic or overwhelming experiences can cause sensitisation, where the puppy becomes more reactive rather than less.

Learned Behaviour

Reactivity often "works" for the dog. When your dog barks and lunges at another dog, that dog usually moves away. From your dog's perspective, their display was effective — the scary thing retreated.

This is why you'll often hear owners say "he's getting worse" — because, from the dog's perspective, the big reaction keeps working. This negative reinforcement powerfully strengthens the behaviour over time.

Traumatic Experiences

A single frightening event can create lasting fear associations. Being attacked by another dog, a painful veterinary procedure, or a scary encounter with a stranger can trigger reactive behaviour that persists long after the original incident.

Pain and Medical Issues

This is frequently overlooked, but critically important. Studies suggest that pain or medical issues are involved in a large proportion of dogs presenting with behavioural problems — some research puts this as high as three-quarters of cases.

Pain lowers your dog's threshold for reactivity. It increases irritability, reduces coping capacity, and can cause sudden behavioural changes. Musculoskeletal problems — particularly hip dysplasia and arthritis — are commonly involved in pain-related aggression cases.

A particularly concerning finding: dogs in pain may show reduced or absent warning signals. They can skip the growl and go straight to snapping because they're too uncomfortable to tolerate any approach.

If your dog's reactivity is new, worsening, or appeared suddenly — especially in an older dog — a thorough veterinary examination is essential before any training begins. No amount of behaviour modification will fix a dog who's hurting.

Understanding Thresholds: Why Reactions Seem Unpredictable

Your dog's threshold is the point where they tip from "coping" to "reacting." Understanding this concept explains a lot about behaviour that seems random or unpredictable.

The Threshold Zones

Green Zone (Under Threshold)

Your dog notices the trigger but stays calm. They can still think, respond to cues, and take treats readily. Their body is relaxed. This is where learning happens — it's the only zone where behaviour modification works.

Yellow Zone (Approaching Threshold)

Your dog is getting tense. They've stopped sniffing, they're staring at the trigger, their body is stiffening. They might still take treats, but roughly or hesitantly. Early stress signals appear — lip licking, yawning, a hard stare. This is your warning. Time to increase distance.

Orange Zone (Over Threshold — Pre-Reaction)

Your dog is highly stressed, 100% focused on the trigger, straining at the leash. They won't take treats or respond to cues. A reaction is imminent. Leave immediately.

Red Zone (Full Reaction)

Hysterical barking, lunging, snapping. Your dog cannot hear you. The thinking brain is completely offline; they're operating on pure instinct. Training is impossible here. Your only job is to get out safely and calmly.

The Threshold Isn't Fixed

Here's what catches many owners off guard: the threshold fluctuates constantly.

Stressful experiences can lower your dog's threshold for hours or even days afterwards, depending on the individual dog and the intensity of the stressor. If your dog had a stressful vet visit, encountered a scary dog, or heard fireworks — their threshold may be much lower than usual.

This "trigger stacking" explains why your dog handled something fine last week but exploded today. It's not random — it's cumulative stress.

A Quick Rule of Thumb

Can your dog take a treat calmly? If yes, you're in the Green Zone — under threshold. If they're grabbing roughly, hesitating, ignoring treats entirely, or can't focus on you — you're approaching or past threshold. Create distance immediately.

Can Reactivity Be Fixed?

Let me be honest with you: for most dogs, the realistic goal is long-term management and significant improvement, not a complete cure. This is similar to managing a chronic health condition like arthritis — you control it, you improve quality of life dramatically, but the underlying tendency may always require some degree of management.

The good news? With proper intervention, most dogs show significant improvement. Clinical experience consistently shows high success rates when medical issues are ruled out and owners follow the treatment plan consistently.

What "Improvement" Looks Like

• Mild to moderate cases: Noticeable improvement within 3-6 months of consistent work
• Severe cases: May take 6-18 months to reach maximum potential
• Progress is incremental — small wins that accumulate over time

Results depend heavily on consistency and avoiding situations that push your dog over threshold repeatedly.

What Affects Success

• Ruling out pain and medical issues first — this is non-negotiable
• Understanding what's driving YOUR dog's reactivity — fear, frustration, or arousal require different approaches
• Consistent management — preventing rehearsal of reactive behaviour
• Appropriate behaviour modification — not just "training," but changing emotional responses
• Medication when needed — in some dogs, medication is essential to bring anxiety down enough for learning to occur. Products like Zylkene or Adaptil may help mild anxiety, but prescription medication may be needed for moderate to severe cases

Is It Too Late If My Dog Missed Socialisation?

No. Improvement is possible at any age. Adult dogs who missed the critical socialisation window can learn to cope much better through counter-conditioning and confidence building.

But the journey is typically longer than for dogs who were well-socialised as puppies, and the goal shifts from "comfortable with everything" to "can cope with life." What matters now is how you respond going forward — not what you could have done differently in the past.

Common Mistakes That Make Reactivity Worse

Beyond avoiding punishment (which increases fear and suppresses warning signals), watch out for these:

Pushing Too Fast

Seeing slight improvement and immediately testing at closer distances. This floods your dog with stress and causes setbacks.

Standing Frozen When Your Dog Reacts

Hoping they'll "get used to it." They won't. It just lets arousal escalate unchecked.

Ignoring Subtle Stress Signals

If you miss the lip licks and yawns, your dog learns they need to escalate to be heard.

Forcing Interactions

Making your dog greet people or dogs when they're clearly uncomfortable. This teaches them their boundaries will be ignored.

Comforting During Reactions

"It's okay, it's okay" while petting can confuse your dog and sometimes keeps them in that emotional state longer. Prioritise calmly creating distance first; you can comfort once everyone is safe.

When to Seek Professional Help

Consider a veterinary behaviour consultation if:

• Your dog's reactivity involves aggression or has resulted in bites
• The behaviour is escalating or becoming unpredictable
• You've tried training without meaningful improvement
• You suspect pain or a medical component
• Your dog's quality of life — or yours — is significantly affected
• You're unsure whether you're dealing with fear, frustration, or something else

A veterinary behaviourist can conduct a medical evaluation, accurately diagnose what's driving the behaviour, prescribe medication if needed, and create a tailored treatment plan.

Trainers can help with obedience and foundation skills, but they cannot diagnose, prescribe, or address underlying medical factors. Ideally, your trainer and vet behaviourist work as a team.

Frequently Asked Questions

The Bottom Line

Reactivity is common, it's manageable, and it's not your dog being "bad." It's an emotional response that tells us your dog is struggling to cope with something in their environment.

With the right approach — ruling out pain, understanding the underlying motivation, consistent management, and appropriate behaviour modification — most reactive dogs improve significantly.

The journey takes time and patience. But you're not alone in this, and there is help available.