The Canine Ledger

Collar or Harness: What the Pressure Studies Show

Collars raise eye pressure and harnesses change how dogs walk. What the studies show, which claims have no evidence, and how to choose for your dog.

Written by thecanineledger

This page carries no advertising, and nothing on it is for sale.

“Much of its use is based on tradition, individual experience and anecdotal evidence”. That’s how a 2026 review in Frontiers in Veterinary Science sums up what we know about collars, harnesses and other gear dogs wear every day (Ridgway, 2026).

While harness makers and plenty of trainers say collars damage dogs’ necks, the research is narrower than the claims. There’s real evidence on eye pressure and on how harnesses change a dog’s stride. There’s almost none on the neck injuries most often cited. This page sets out which is which.

1. Eye pressure: the strongest evidence

A 2006 study measured eye pressure in 51 eyes of 26 dogs while pressure was applied through a collar or a harness. “Intraocular pressure increased significantly from baseline when pressure was applied via a collar but not via a harness” (Pauli et al., 2006).

The authors advise that “dogs with weak or thin corneas, glaucoma, or conditions for which an increase in IOP could be harmful should wear a harness instead of a collar, especially during exercise or activity.” IOP means intraocular pressure, the pressure inside the eye.

A 2025 UK study looked at flat-faced (brachycephalic) dogs and long-nosed dogs. It recruited 24 dogs and analysed 20. In the flat-faced dogs, “Just wearing a collar in a stationary condition increased IOP”. The authors conclude that collars “may elevate IOP during exercise for all dogs and also during stationary conditions for brachycephalic breeds” (Bailey et al., 2025).

Both studies are small, and neither followed dogs long enough to show eye damage. Still, they point the same way.

Our note: We don’t know whether a rise in eye pressure of this size matters in a healthy dog. It may matter more for dogs with glaucoma or thin corneas.

2. Neck pressure: a model, not a dog

A 2020 study tested seven collars and a slip lead on a plastic model neck with a pressure sensor underneath. “Collars exerted a pressure of between 83 kPa and 832 kPa on the model neck.” The authors conclude that “No single collar tested provided a pressure considered low enough to mitigate the risk of injury when pulling on the lead” (Carter et al., 2020).

That’s a useful warning. It isn’t proof of injury. The 2026 review notes that the results “may not reflect collar impacts on the far more structurally complex live canine neck”, where skin and muscle can shift and absorb force.

3. Neck injuries: claimed, not shown

You’ll often read that collars damage the thyroid, the windpipe or the blood vessels in the neck. The 2026 review looked for evidence:

  • “Other claims of collar-related injury due to leash-pulling, such as damage to the thyroid gland, trachea, jugular veins, or carotid arteries, are not supported in the literature”.
  • “There is no reported documentation of tracheal trauma from chronic use of a collar for training despite claims to the contrary.”
  • “Accessing the references for such claims reveals the lack of actual evidence.”

That doesn’t mean collars are harmless. It means nobody has studied it properly. The review says it is “unknown” whether repeated low-level collar pressure has measurable health effects.

Dogs with a collapsing windpipe are different. The review cites a study in which, for dogs with existing tracheal collapse, collar-level pressure “severely compromised the tracheal lumen”, the airway. If your dog has a cough or a known airway problem, ask your vet before using a collar.

Our note: The tracheal-collapse point comes from a study cited inside the review, which we haven’t read ourselves. If your dog has an airway problem, ask your vet about collars.

4. Harnesses change how dogs walk

Harnesses aren’t free of trade-offs. The review reports that “in all reported studies of harnesses and canine gait, all investigated harness types have impacted gait.”

One surprise: in a study comparing designs, “non-restrictive harnesses actually restricted shoulder extension more than restrictive harnesses at both gaits”. Non-restrictive harnesses are the Y-fronted kind that don’t cross the shoulder.

Whether this matters is unknown. The review says the risk of these gait changes leading to joint or muscle problems, “although suspected, has not been documented.”

5. How to choose

A 2025 review commissioned by the BC SPCA, a Canadian animal welfare charity, reached a practical view: “no single device works best for every dog, and the right choice depends on the dog and the guardian’s needs” (Cavalli & Protopopova, 2025). Its suggestions:

Your dogThe review’s suggestion
Pulls on the lead“non-tightening front-clip harnesses appear to offer the best balance between discomfort and reduction in pulling.”
Flat-faced, or doesn’t pull“back-clip harnesses are suitable, especially those with a chest-strap or a Y-shape.”
Walks without pulling“Flat collars are appropriate for dogs that consistently walk without pulling, as they produce the least body restriction.”

The same review notes that earlier research “has advised against the use of aversive collars (such as choke, prong, or electric collars)”. → E-Collars, Prong and Choke Collars: The Evidence and the Law

Fit matters with any of them. The review warns that “poor fit is an ongoing concern that can increase the negative impact of any restraint method”.

Our note: The review’s author was contracted by the BC SPCA. Puppies and dogs with neck or back pain may need different advice.

6. What we could not verify

Commonly saidWhat we found
“Collars damage the thyroid”No published evidence, the 2026 review says.
“A collar puts many times more pressure on the neck than a harness”We couldn’t trace a figure. The model-neck study tested collars and a slip lead, not harnesses.
“Harnesses are always better”Not proven. Every harness studied changed how dogs walk.
“Collars raise eye pressure”Yes, in small studies. Most relevant for dogs with eye disease and flat-faced breeds.

Sources

Always confirm with your vet before acting on anything on this page.