Harness or collar for small dogs? What science says

It's one of the first questions when a dog arrives home, especially if it's a small one: collar or harness for walks? We aren't going to give you an opinion here, but rather what Spanish law and published veterinary studies say. We will also cover their limitations, because the science on this subject is still limited.

First, what the law in Spain says

Since September 29, 2023, Law 7/2023 on the protection of animal rights and welfare prohibits in its Article 27 the use of any handling tool that could cause injury to the animal, and specifically mentions electric, impulse, punishment, or choke collars.

A regular flat collar, properly adjusted, is not prohibited. The question, therefore, is not legal but health-related: what is better for your dog's neck and body?

A small dog's neck is delicate

Tracheal collapse is a weakening of the cartilage rings of the trachea. According to the Merck Veterinary Manual, it is more frequent in toy and miniature breeds and manifests as a dry cough that sounds like a honk and difficulty breathing.

In dogs with this problem, the veterinary recommendation is clear. The owner's guide from the University of Tennessee College of Veterinary Medicine indicates that a harness should be used instead of a collar.

Note: that does not mean a collar causes tracheal collapse in every dog. It means that if your dog is a small breed or already coughs when pulling on the leash, it is advisable not to put pressure on the neck.

Neck pressure also affects the eyes

A study published in 2006 in the Journal of the American Animal Hospital Association (Pauli and colleagues) measured intraocular pressure in 26 dogs (51 eyes) while they were pulling with a collar and with a harness. Ocular pressure rose significantly with the collar, but not with the harness. The authors recommend that dogs with glaucoma, thin corneas, or any condition where increasing ocular pressure is harmful should use a harness, especially when exercising.

A more recent study from 2025 (Bailey and colleagues, Veterinary Medicine and Science) reached a similar conclusion with 20 dogs: walking with a collar increased ocular pressure in all groups, while walking with a harness did not. In short-snouted (brachycephalic) dogs, simply having the collar on and the leash taut was enough, even without walking.

But the harness isn't perfect either

To be fair, we must share the other side of the story:

• Some harnesses limit shoulder movement. The Norwegian harness can limit movement. Its horizontal strap crosses in front of the shoulders and, due to its shape, can restrict the movement of the front legs while walking. In general, any harness modifies how they move slightly, so the important thing is that it is well-adjusted and that your dog walks naturally.
• With a harness, many dogs pull more. In the 2006 study cited above, the dogs generated more force when pulling with a harness than with a collar. Presumably, because they don't feel pressure on their neck, they pull more comfortably.

And an important warning: almost all these studies are small, with between 9 and 26 dogs. They point in one direction, but they are not the final word.

So, what should we choose?

Based on what is known today, this is a reasonable guide:

• Toy and small breeds (toy poodle, Yorkshire, Chihuahua, Pomeranian…): harness for walking. These are the breeds most at risk of tracheal problems.
• Dogs that pull on the leash: a harness, so that the pressure does not fall on the neck. And, in parallel, work on loose-leash walking.
• Short-snouted breeds (French bulldog, pug…) or dogs with eye problems: a harness.
• Dogs that already walk without pulling: a wide, flat collar, properly adjusted, is a legal and valid option.

A very practical combination: a flat collar only for the identification tag and a harness for attaching the leash.

How to know if a harness fits well

• You should be able to fit two fingers between the harness and the body, no more, no less.
  
• It should not twist or slide to one side when walking.
• Measure the neck where the collar would go and the chest at its widest part, just behind the front legs. If it falls between two sizes, choose the larger one.

In each listing of our harness, leash, and poop bag holder sets, you have the size chart with neck and chest measurements, from XS to M.

Frequently Asked Questions

Does a harness make my dog pull more? 
It can happen: by not feeling pressure on the neck, some dogs pull with more force. The harness protects the neck, but it does not replace leash training.

What type of harness is best?
The few studies that exist do not allow us to say that one model is best for all dogs. The most important thing is that the size is correct and that the harness does not chafe or limit natural movement. 

Sources

• Law 7/2023, of March 28, on the protection of animal rights and welfare, art. 27. BOE-A-2023-7936.
• Merck Veterinary Manual. Tracheal Collapse in Dogs.
• Tobias, K. University of Tennessee College of Veterinary Medicine. Tracheal Collapse.
• Pauli AM, Bentley E, Diehl KA, Miller PE. Effects of the application of neck pressure by a collar or harness on intraocular pressure in dogs. J Am Anim Hosp Assoc. 2006;42(3):207-211. PubMed.
• Bailey ME, Packer MJ, Wills AP. Effect of a Collar and Harness on Intraocular Pressure and Respiration Rate of Brachycephalic and Dolichocephalic Dogs. Vet Med Sci. 2025;11(3):e70384. PMC.
  

This article is for informational purposes and does not replace a consultation with a veterinarian.