Harness or collar for a puppy? What the neck pressure studies show

Use both. A flat collar carries the ID tag, which the law in England, Scotland and Wales requires in public, and a harness takes the lead so the pull lands on the chest instead of the neck. The case for the harness rests on measured pressure: no collar tested on a model neck in a 2020 study kept the pressure low enough to cut the risk of injury when the lead was pulled, and collars raised the pressure inside the eye where a harness did not. A back clip harness does not stop pulling, though, and can increase it. Training does.

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Which one for your puppy

For most puppies the answer is a flat harness for the lead and a light collar for the tag. Some dogs have more reason than others to keep the lead off the neck.

These are the 32 breeds Puplr treats as flat faced:

And 20 more in the breed guides.

What the studies measured

Studies of collars and harnesses are few and small. A 2026 review of dog equipment found "a paucity of evidence regarding best designs and best practices". Here is what has been measured.

• Pressure on the neck. A 2020 study pulled seven collars and a slip lead against a model neck, at a firm pull, a strong pull and a jerk. "Collars exerted a pressure of between 83 kPa and 832 kPa on the model neck", and "No single collar tested provided a pressure considered low enough to mitigate the risk of injury when pulling on the lead." The model was a plastic cylinder, and the review notes the results "may not reflect collar impacts on the far more structurally complex live canine neck".
• Pressure in the eye. In 26 dogs, "Intraocular pressure increased significantly from baseline when pressure was applied via a collar but not via a harness." A 2025 study of 24 dogs repeated it: "Exercising in a collar increased IOP for both groups of dogs", "whereas exercising in a harness did not affect IOP for either group".
• The windpipe. The review found "There is no reported documentation of tracheal trauma from chronic use of a collar for training despite claims to the contrary." The exception is a windpipe that is already weak: a normal trachea withstood 20 mmHg without the airway closing, but in dogs with tracheal collapse "20 mmHg collar pressure severely compromised the tracheal lumen."
• Pulling. In a study of 52 shelter dogs reaching for food, "The maximal and mean leash tension and the pulling time were greater under restraint by harness", a harness clipped on the back. The review describes a second study with the same result. A 2024 study of 23 dogs found dogs pulled less in a front clip harness than in a martingale collar.
• How the dog moves. In a study of nine dogs, both harness types reduced shoulder extension, and the Y fronted type, the kind labelled non restrictive, reduced it more. The review says "all investigated harness types have impacted gait", that the effect varied by breed in a study of 66 dogs, and that whether this causes problems "although suspected, has not been documented."

What to look for

• A harness that fits now and adjusts. RSPCA Australia: "If you have a medium or large breed puppy, you will need to purchase a small collar/harness initially, and reinvest in new collars as your dog outgrows them."
• A puppy that walks normally in it. RSPCA South Australia's test: "If they walk differently with the harness on, then it isn't comfortable", and "A properly fitted harness won't restrict the dog's movement and they'll be able to take full strides on their front feet." Dogs Trust says to avoid harnesses that "cross directly in front of the shoulders preventing natural movement".
• Snug enough to stay on. Dogs Trust: "You should be able to fit a finger comfortably between the strapping and their body", and "Your dog shouldn't be able to slip out of it." RSPCA South Australia warns that if it is too loose, "the dog can slip an elbow through the straps and back out of it".
• Easy to put on. Dogs Trust notes that some harnesses "clip around the neck and body", which "might be better for dogs who are a little head-shy."
• A light, flat collar for the tag. The Royal Kennel Club: "Choose a small, lightweight one that's suitable for the size they are now." It should not slip over the head, "nor so tight that you cannot slip two fingers underneath." Clip the lead to the collar's D ring, never "the split ring that attaches the identity tag".
• A plain lead of about 2 metres. RSPCA Australia says a lead should give room to explore at "approximately 2 metres", and that "Extendable, retractable or bungee leashes are not recommended."

Claims that do not hold up

"A collar will damage a puppy's windpipe." Not shown for a healthy dog. The 2026 review found no documented tracheal injury from everyday collar use. Blue Cross does say "Coughing is common when a dog is pulling on their lead and the collar is putting pressure on their windpipe", and the dogs with a collapsing trachea are a real exception. The stronger case for a harness is the measured neck and eye pressure.

"A back clip harness stops pulling." Two studies found dogs pulled harder in a back clip harness than in a collar (in one, only when reaching for food), and the review concludes that the evidence supports "that dogs pull harder or at least as hard in a harness". What stops pulling is training: RSPCA Australia's method is to stop and "stand still like a tree" when the lead goes tight.

"A Y front harness leaves the shoulders free." Harnesses that do not cross the shoulder are labelled non restrictive. In the 2019 study they reduced shoulder extension more than the type with a strap across the chest, though only nine dogs took part. Watch how your own puppy moves in it.

"A choke chain or prong collar is fine if used properly." RSPCA Australia: "Check chains (choker chains or slip collars) or pronged/pinch collars must not be used as they cause pain and distress to animals, and can cause damage to the neck." The 2026 review says choke collars "are believed to pose the greatest risk" of strangulation injury. The 2024 study did find dogs pulled less on prong collars than on a martingale collar, but it found the same of a front clip harness, so pulling less is no argument for a prong collar.

"Buy the adult size so it lasts." The Royal Kennel Club: "Don't get one you think they'll grow into eventually". Too loose is how a puppy backs out of a harness, and the review notes that embedded collars are often "related to circumstances where a dog grew without having its collar resized".

"A microchip means no collar." Not in Great Britain. The Control of Dogs Order 1992 says a dog in a public place "shall wear a collar with the name and address of the owner", and GOV.UK says a microchipped dog "must still wear a collar and tag with your name and address when in a public place."

The kit

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How to get a puppy used to it

1. Collar first, with a treat. The Royal Kennel Club: "put on the collar and immediately after give them a treat". Not after taking it off, "otherwise all you're rewarding them for is having the collar off."
2. Then the harness, slowly. Dogs Trust's steps: scatter treats around the harness on the floor, feed treats through the head opening, let it hang loosely round the neck, let the puppy hear the clips, then do it up and play. "If they retreat, simply remove the harness straight away and go back a stage."
3. Start indoors. The Royal Kennel Club says to introduce the lead in the house first, and "The most important thing is to never pull on the lead."
4. Stop when the lead goes tight. Dogs Trust: "The second the lead starts to tighten, stop walking." Reward the puppy for being by your side, every few steps at first.
5. Check the fit as they grow. The Royal Kennel Club says to check collars "almost daily"; RSPCA Australia says "at least a few times a week", for the harness too. Puppies grow fast, and at six months they still have growing to do. The growth chart behind Puplr's size predictor puts them here:

Share of adult weight from the growth data behind Puplr's adult size predictor. Size classes are the AKC chart's own, by adult weight; they are not standard between organisations. Source.

1. Take the collar off in the crate. The Royal Kennel Club: "Always remove the puppy's collar when in the crate in case it gets caught up on it."
2. Use the walks for socialisation. The socialisation checklist has what to meet, week by week.

Common questions

Should a puppy wear a collar or a harness?

Both. A collar for the ID tag, which the law requires in England, Scotland and Wales, and a harness for the lead. Dogs Trust: "to comply with the law, when you are in public spaces you will need to make sure your dog also wears a dog collar, with an identity tag attached to it, even if you are walking them in their harness."

Front clip or back clip harness?

While you teach loose lead walking, Dogs Trust says to use "whatever piece of equipment is most comfortable for them, such as a flat harness or collar." For a dog that keeps pulling, RSPCA Australia recommends a front clip harness and a double ended lead, one end on the front and one on the back. In the pulling studies, dogs pulled as hard or harder on a back clip harness than on a collar, and less on a front clip harness than on a martingale collar.

Is a harness bad for a puppy's shoulders?

Every harness studied changed how dogs move, but the 2026 review says harm from it "although suspected, has not been documented." Fit matters most: check that your puppy takes full strides with it on, as RSPCA South Australia suggests, and adjust or change it if not.

Should my puppy wear a collar at home?

The Royal Kennel Club says to "Keep an eye on them in case the collar gets caught on anything such as furniture", but also that a collar or harness on in the house can help you catch a puppy that is quick to escape. Always take it off in the crate.

What about a head collar?

The sources differ. RSPCA Australia says front clip harnesses have largely taken their place and "Many dogs do not tolerate head collars". For a large or strong dog that is hard to handle, Battersea says "A well-fitted head collar can help you stay in control while you build good habits, as long as it's introduced slowly and positively." Try a front clip harness first.

How we worked this out

We did not test any harnesses or collars. This guide is built from peer reviewed studies, a 2026 review of dog worn equipment, welfare charities in the UK, Australia and the US, a kennel club, UK law and GOV.UK, all opened and read on 4 October 2026 and quoted word for word where they are quoted. Every source is listed below.

The dog studies are small, 9 to 66 dogs each, and the neck pressure study used a plastic model rather than a dog. None of them studied puppies specifically. The flat faced list is the one Puplr uses on its breed pages and what to buy, from Puplr's 384 breed records. The share of adult weight comes from the AKC growth chart behind the adult size predictor.

Where the sources disagree, we have said so. The main differences:

• Harness shape. Dogs Trust says to avoid harnesses that cross directly in front of the shoulders, without naming a design. The 2019 study found both types reduced shoulder extension, the Y fronted type more, and the 2026 review says the effect varies by breed.
• How snug. Dogs Trust says a finger under the straps; RSPCA South Australia says two fingers.
• How often to check the fit. The Royal Kennel Club says almost daily; RSPCA Australia at least a few times a week.
• Collars and the windpipe. Blue Cross says a harness can "prevent any damage to your dog's neck or windpipe"; the 2026 review found no documented tracheal injury from everyday collar use in healthy dogs.
• Retractable leads. RSPCA Australia does not recommend them; Battersea says they "can be used if you fix them at a set length rather than letting them extend".
• Head collars. RSPCA Australia puts them after a front clip harness; Battersea suggests one for a large or strong dog that is hard to handle.

This guide was drafted with an AI writing tool and checked against every source listed. Read more about how we write buying guides.