The tracheal collapse argument
Small breeds — Yorkies, Pomeranians, Chihuahuas, Shih Tzus, toy Poodles — have genetically weak tracheal cartilage. A collar pulling on that thin windpipe, even once, can cause microscopic damage. Over years of daily walks, that damage accumulates into diagnosed tracheal collapse: coughing, wheezing, exercise intolerance, surgery.
Harnesses don't touch the neck at all. For these breeds, a harness isn't optional — it's the difference between a healthy 14-year-old Chihuahua and a 10-year-old one on chronic medication.
Flat-faced breeds (brachycephalics)
Pugs, French Bulldogs, English Bulldogs, Boston Terriers, and Pekingese already have compromised airways. Any collar pressure makes their breathing worse. These breeds should never walk on a collar — full stop. A harness (preferably a soft mesh one like Puppia) is mandatory.
The pulling problem
For pullers, a flat collar doesn't just hurt — it's also ineffective. Dogs lean into collar pressure (opposition reflex). A front-clip harness redirects their momentum sideways when they pull, which naturally teaches loose-leash walking without pain.
Front-clip harnesses like the Ruffwear Front Range, Rabbitgoo No-Pull, or PetSafe Easy Walk are purpose-built for this. Using one alongside treats and consistency turns most pullers into loose-leash walkers within a few weeks.
When collars are fine for walking
Not every dog needs a harness for walks. If all the following are true, a collar is reasonable: - Medium to large breed (over 30 lbs) - Healthy neck and airway - Trained to walk without pulling - Short walks only, not long hikes
Even then, a flat collar should fit properly — two fingers between the collar and neck, never tight enough to restrict breathing.
The dual-gear approach
Most experienced owners use both: collar for ID tags (always on) plus harness for walks. The collar holds the rabies tag, city license, and contact info in case of escape. The harness provides safe walking control. This isn't redundancy — it's belt and suspenders, and it's what most trainers recommend.