How to Treat Puppy Leash Aggression

Aggression is usually rare in puppies. Some dogs can start displaying reactivity at a young age, though! If you're worried about puppy leash aggression—or think your family's new addition might become leash reactive—you've come to the right place.

Here are some key things to know. You can help your pup grow up into a happy, confident, well-behaved dog! We cover:

• Definitions of leash aggression and leash reactivity
• Types of leash reactivity (fear and frustration)
• How leash aggression develops in young dogs
• How to tell if your puppy has leash reactivity—or if their behavior is normal for a young dog
• If puppy leash aggression leads to adult behavioral problems
• Further dog reactivity resources

1) Are leash aggression and leash reactivity the same thing?

Everyone’s favorite answer: It depends.

Many dog trainers, pet parents, and veterinarians use "leash aggression" and "leash reactivity" interchangeably. They terms can have slightly different nuances in meaning, though, depending on who you ask.

Leash aggression definition

Leash aggression refers to a dog displaying aggressive behavior on a leash. It can manifest as growling, barking, lunging, or even attempting to bite.

Leash reactivity definition

Leash reactivity can be a broader term. Reactivity might encompass a range of behaviors your dog exhibits while on a leash—not only traditionally aggressive behaviors but also fearful, anxious, or overly excited emotional responses.

Per Sniffspot's proprietary survey research, 66% of dogs are reported by their guardians to be reactive. Of these, 65% are leash reactive specifically.

We treat leash aggression and leash reactivity similarly

Both "leash aggression" and "leash reactivity" refer to undesirable behaviors (like barking, growling, lunging, whining and pulling) your puppy might show when they encounter a specific trigger (like other pets, strangers, bikes, or cars) on leash. In this article we’ll use both terms interchangeably.

2) What's at the root of most leash aggression and leash reactivity?

More often than not, leash reactivity is caused by one of two major F-words: Fear and Frustration.

Typically, a reactive dog on leash has one of two goals in mind. They either want to get away (fear) or get closer to something in the surrounding environment (frustration).

Fear-based leash reactivity: Dogs have a negative association with a scary stimulus

In fear-based leash reactivity, something your dog is afraid of triggers their fight-or-flight response. No matter which of those two instincts they follow—or if they "freeze" or "fret" instead—the key thing to know is they feel trapped by their leash.

Even a dog who wants to run from a perceived threat can fall back on seemingly aggressive behavior, like barking and growling, in these situations. This is intuitive once you think about it: A puppy's leash makes fleeing impossible. When we remove the flight option by holding our dogs still on a leash, we leave them with fight as a go-to fearful response.

Dogs experiencing fear-based leash reactivity will often seem even more aggressive than their excitable, frustration-based reactive counterparts. Anyone with a tiny dog who becomes a barking machine at the sight of any bigger dog on walks knows this all too well!

Frustration-based leash reactivity: Dogs want to access something in their environment but can't

Frustration-based leash reactivity stems from a dog’s unmet desires. This could be anything, like the:

• desire to play with another dog on a walk
• impulse to run up and say hi to every human they see
• deeply-ingrained need to chase all squirrels, birds, and other small creatures

Just because a dog wants to do something, however, doesn’t mean they should. Take the all-too-common doggy desire to dart into traffic and chase cars, for example.

While using a leash is a fabulous way to manage these situations, it's inevitable that some undesirable replacement behaviors might bubble up when we restrict our dogs from following their natural urges.

3) How does leash reactivity usually develop in dogs?

Leash reactivity can show up at various ages in our pet dogs. There's no specific timeline or turning point. That said: Certain factors may contribute to the development of leash reactivity at different life stages.

Reactive behaviors are common in teenage dogs

Pet owners commonly observe leash reactivity during their dogs' adolescent phase. (This period falls between six months and two years of age.)

During canine adolescence, hormonal changes, increased independence, and a heightened sensitivity to the environment can contribute to reactive behaviors. Sometimes dogs outgrow these struggles on their own. Other times they’re a sign of a long-term struggle.

Regardless, it’s important to help your teenage dog through their reactive displays! (More on actually dealing with aggression and reactivity later.)

Socialization can prevent reactivity and aggression

If you haven't been able to adequately socialize your dog during their critical period of puppyhood (up to around 16 weeks of age), they may be more prone to developing reactivity. This is especially true if they have a bad experience later on. (More on that next.)

No matter how you slice it, early positive associations and exposure to various stimuli—including people, animals, and environments—is vital for your pup's development.

Dogs (especially puppies) can experience single-event learning

Dogs that have a negative experience while on a leash—like if they're attacked by another dog or forced to sit still around frightening stimuli—may develop reactivity across the board. This is a protective response to one trial learning.

Traumatic events can contribute to fear-based reactivity at any age. They're particularly risky when dogs are young and impressionable, though.

Negative single event learning can be even more harmful than a lack of socialization. That means it's important for dog guardians to be on the lookout for fearful behaviors. Make thoughtful risk assessments when exposing your dog to the world!

Environmental stress can contribute to reactivity

Changes in a dog's living environment and routine, or exposure to new situations they've never seen before, can trigger reactive behaviors.

4) How do I know if my puppy has leash aggression—or if they're just excitable because they’re young?

Distinguishing between leash aggression and simple excitable behavior in a puppy can be challenging. Both might involve:

• barking
• pulling on the leash
• biting at their leash
• and other energetic reactions out on your walks.

You don’t want to panic about your dog’s long-term behavior if it’s just a normal phase. You also want to take any signs of reactivity you see seriously so that you can start helping your pup right away! What's a new dog parent to do?

Here are some concepts to help you determine if your puppy is becoming a leash-aggressive dog.

Body language

An excitable puppy will exhibit loose, wiggly body language. They probably have a bouncy or playful demeanor—without the intense tight posture seen in many forms of leash reactivity or aggression in adult dogs.

Nervous dogs are more likely to show the whites of their eyes (this is called whale eye) as well as dilated pupils, often while lip licking. They might struggle to break eye contact with their triggers as they display these early warning signs of discomfort.

Trigger specificity

Leash aggression occurs in response to specific triggers. These triggers might include the presence of strange dogs, unfamiliar people, or certain environmental stimuli.

Excitability, on the other hand, may be caused by a variety of things—or nothing at all—including the anticipation of play, novel experiences, or simply the wind blowing in the breeze.

Consistency of behavior

Leash aggression tends to be consistent in specific situations or with certain triggers. It is not solely linked to moments of high energy or excitement.

Ease of redirection

An excitable puppy is more likely to respond positively to redirection, like training cues or a change in focus, than a dog who is deeply afraid of a particular trigger. They may quickly shift from excitement to a calmer state—or at least be able to pay attention back to you more easily. Excited puppies also probably show more confidence on leash in general. This makes it easier for them to offer you eye contact and keep a loose leash instead of fixating on the world around them.

5) If my dog is leash reactive as a puppy, does that mean their behavior will be even worse in adulthood?

Leash reactivity in a puppy does not necessarily predict that the behavior will be worse in adulthood. A puppy's behavior is still highly malleable! Training interventions can be particularly effective at a young age.

That said: A very young dog displaying leash aggression might suggest the behavior is at least in part genetic. This means it could be more difficult to completely address.

Regardless of your individual dog’s history and predispositions, the most important thing is to address reactivity as early as you can. Start with a comprehensive exam by a veterinary professional. The right, humane training methods and proper socialization experiences can go a long way!

6) Further reading and learning

There are countless great resources for how to live with and train a reactive dog! Here are a few of our favorites.

Sniffspot blogs on canine reactivity

We have an entire blog category devoted to dog reactivity and related problem or unwanted behaviors. One of our primary goals is to be a welcoming community for reactive dogs. That’s why we have intentional rules (like gaps between arrivals and transparency about other animals within view) to keep all Sniffpot private dog parks safe.

Here are a few specific articles:

• How to Train a Reactive Dog: A Beginner’s Guide for everything you need to know to get started implementing a training program for your reactive dog, including how to set up some initial training sessions and supplies you need to have on hand (like high-value treats, a treat pouch, sometimes a basket muzzle, and more)
• How to Socialize Your Reactive Dog for help on how to give your fearful, frustrated, or otherwise reactive dog positive experiences with other dogs and people
• Dog Reactivity Chart for help understanding the current level of reactivity your dog shows in different moments

Other training resources on dog reactivity

• Trainer Patricia McConnell’s guide to how to handle reactive dogs
• CARE For Reactive Dogs is a whole website dedicated to methods and gear for dealing with a reactive dog
• Suzanne Clothier reactive dog training scenario set up
• Trainer Alice Tong’s engage-disengage game (specific to leash reactivity, but can be applied to other types of reactivity as well)
• The VCA’s guide to counterconditioning and desensitization 

Good luck, and remember you’re not alone. When in doubt, get in touch with a professional force free trainer or veterinary behaviorist you trust. (They should be able to help you rule out medical conditions, choose the right training tools, implement counter-conditioning, and teach you about other behavioral therapy).

And know you can always bring your dog to a Sniffspot for some playtime!

Trainer Review of this Article

There is so much misinformation out there, and we want to make sure we only provide the highest quality content to our community. We have our articles reviewed by qualified force free trainers.  

This is the trainer that reviewed this article:

Shannon Finch
AnimalKind Training
M.Ed. Humane Education
Karen Pryor Academy Certified Training Partner
Certified Tellington TTouch and TTEAM Practitioner

Sniffspot's Proprietary Survey Statistics

Sniffspot Research 2023, n = 4,092