Dog lunges at other dogs on leash: why it happens and what to do

Most dogs that bark and lunge at other dogs on leash are scared or frustrated, not "dominant." The ASPCA calls it leash reactivity and names two common causes. Some dogs fear other dogs, and lunging works: the other dog goes away. Others love dogs so much that being held back by the leash frustrates them.

The leash itself makes it harder. Off leash, dogs greet in a slow curve. On a sidewalk they meet head-on, staring, with tight leashes and collars pressing on their necks. So many dogs are fine at the park and loud on the street.

What helps is distance. Every reactive dog has a threshold: the distance at which they notice another dog but don't bark or lunge. Train just beyond that line, where your dog can still eat, listen and learn that other dogs predict good things.

Find your dog's trigger distance (free check)

What to do in the moment

Too close already? Get through it calmly; training can wait.

Make space early. Cross the street, step between parked cars or turn and walk the other way. A practiced U-turn ("this way") makes it easy.
Keep the leash loose. The San Francisco SPCA notes that a tight leash passes your tension to your dog.
Scatter food on the ground. Toss treats in front of your dog and keep tossing until the other dog has passed. The SF SPCA calls this "find it."
Break the stare before the lunge. The ASPCA says a dog staring at something for two seconds or more is likely deciding whether to lunge. Call your dog's name and move away before that point.

What not to do: corrections, prong and choke collars

Leash pops, prong collars and choke chains can stop a lunge for a moment. The evidence says they cost more than they fix.

The American Veterinary Society of Animal Behavior's position statement on humane dog training (2021) says to avoid choke chains, prong collars, shock collars and leash jerking. It lists the fallout as more anxiety, fear-related aggression and avoidance, and finds no evidence that aversive methods work better than rewards in any context.
A 2017 review by Ziv found no evidence that punishment works better than reward-based training, and some evidence that it works worse.
A 2020 study by Vieira de Castro and colleagues compared dogs at training schools. Dogs at schools that used aversive methods showed more stress behaviors, had larger rises in cortisol after training, and were more "pessimistic" in a later test.
A 2014 study by Deldalle and Gaunet watched dogs walking on leash and sitting on cue. Dogs from a school that trained with pressure released when the dog complied showed more stress signals; dogs trained with rewards looked at their owners more.
The SF SPCA warns that choke, pinch and shock collars cause pain, which does not reduce frustration and can make aggression worse.

A 2009 survey by Herron, Shofer and Reisner asked 140 owners at the University of Pennsylvania's behavior clinic what they had tried and whether their dog responded with a growl, snap or bite. Some of their numbers:

What owners tried	Dogs it was tried on	Responded aggressively
Hit or kick the dog	28	43%
"Alpha roll"	36	31%
Yell "no"	122	15%
Choke or prong collar	53	11%
Leash correction	105	6%
Food rewards	124	2%
"Look" or "watch me"	62	0%

It surveyed dogs already at a behavior clinic, so it shows a link, not proof of cause. The authors note a correction can briefly stop the behavior, which looks like improvement.

A step-by-step plan

The approach is desensitization (the trigger in small doses, far enough away) and counter-conditioning (the trigger predicts food): gradual exposure that, in AVSAB's words, keeps the dog feeling safe at all times.

Rule out pain. Book a vet check if the lunging started suddenly or your dog seems stiff, sore or touchy (see below).
Find the trigger distance. Note how far away another dog is when your dog first notices it but stays quiet. The ASPCA's example: if that distance is 40 feet, start training at about 50.
Teach the skills at home first, with no dogs around. A name game, a hand target (nose to palm), a mat settle, a U-turn on "this way" and "find it." A dog can't look at you and lunge at the same time, as the ASPCA points out.
Pay for every sighting. When your dog sees a dog at a safe distance, feed treat after treat. When the dog leaves, the food stops. This is often called "look at that."
Close the gap slowly. The ASPCA advises moving more gradually than you think you should, because going faster than the dog can handle undoes progress. A simple rule: after three calm sessions, move 5 feet closer; after three or more reactions, add 25% more space.
Log every walk. Distance, dogs seen, how your dog did. The log tells you when to move closer.
Manage the rest of the time. Walk at quiet hours and quiet places while you train. The ASPCA notes that the more a dog practices lunging and barking, the better he gets at it.

This is the method our plan follows, day by day: see how the plan works, or look at a sample day.

How long it takes

It depends on the dog. The ASPCA says some food-loving dogs who are only mildly frustrated improve in a session or two, but most need many sessions over days or weeks for a lasting change. Expect setbacks: the ASPCA warns that each push too close risks one, so a bad day usually means more distance, not a new method. For serious fear or aggression, AVSAB notes that medication from a vet may be part of the plan.

When to see a vet or a veterinary behaviorist

Possible pain. A 2020 paper by Mills and colleagues reviewed 100 dog cases referred for behavior problems and estimated that around a third involved a painful condition, nearly 80% in some caseloads. A sudden change, limping or flinching when touched is a reason to see your vet first.
Bites. The ASPCA advises professional help if your dog has bitten a person or another animal, ideally a board-certified veterinary behaviorist (DACVB) or a certified applied animal behaviorist. If your dog has bitten and broken skin, see a veterinary behaviorist before you start any home plan. Find one in the specialists' directory.
Still reactive after working through these steps: the ASPCA advises a qualified behavior professional.

Questions owners ask

Is my dog aggressive or dominant?

Usually neither. The Herron study's authors point to research showing that aggression problems in dogs come from fear or anxiety, not from a bid for "alpha" status.

Will he grow out of it?

Don't count on it. Each lunge is practice. The ASPCA also warns that cutting walks short to avoid dogs can leave a dog more agitated and less sociable.

Should I let him meet the other dog to make friends?

Not while you are training. A tight, head-on leashed greeting is what sets off many dogs.

What should he wear?

Both the ASPCA and the SF SPCA suggest a head halter or a front-clip harness for management, introduced slowly so your dog is comfortable in it. Skip prong, choke and shock collars. If your dog pulls on every walk, not only near dogs, read dog pulls on leash, tried everything.

Find your dog's trigger distance (free check)

Sources

ASPCA. Dogs who are reactive on-leash. Updated May 4, 2020. aspcapro.org
San Francisco SPCA. Dog-dog aggression on leash (reactivity). sfspca.org
American Veterinary Society of Animal Behavior. Position statement on humane dog training, 2021. avsab.org
Ziv G. The effects of using aversive training methods in dogs: a review. Journal of Veterinary Behavior 19 (2017): 50–60. doi.org/10.1016/j.jveb.2017.02.004
Vieira de Castro AC and colleagues. Does training method matter? PLOS ONE 15(12) (2020): e0225023. journals.plos.org
Deldalle S, Gaunet F. Effects of 2 training methods on stress-related behaviors of the dog (Canis familiaris) and on the dog–owner relationship. Journal of Veterinary Behavior 9 (2014): 58–65. doi.org/10.1016/j.jveb.2013.11.004
Herron ME, Shofer FS, Reisner IR. Survey of the use and outcome of confrontational and non-confrontational training methods. Applied Animal Behaviour Science 117 (2009): 47–54. vmc.vet.osu.edu
Mills DS and colleagues. Pain and problem behavior in cats and dogs. Animals 10(2) (2020): 318. doi.org/10.3390/ani10020318
American College of Veterinary Behaviorists. Find a board-certified veterinary behaviorist. dacvb.org