French Bulldogs have topped the American Kennel Club's most-registered-breed list for four years running, and Pugs and Boston Terriers aren't far behind. All three share the same flattened, wrinkled face that makes them instantly recognizable and, according to a growing stack of veterinary research, makes many of them work harder than they should just to breathe.
What the Research Actually Found
A 2025 cross-sectional study examined 898 dogs across fourteen brachycephalic breeds for brachycephalic obstructive airway syndrome, known as BOAS in veterinary literature. The results were stark. Only the Maltese and Pomeranian in the study group came back with no clinically significant cases. Everything else showed some level of breathing abnormality, and two breeds stood out as the worst affected: just 10.9 percent of Pekingese and 17.4 percent of Japanese Chin tested as fully unaffected. French Bulldogs, Pugs, and English Bulldogs landed in a similarly rough range in earlier studies, with unaffected rates estimated around 7 to 11 percent.
Researchers found three factors that reliably predicted risk: a higher body condition score (heavier dogs breathed worse), narrowed nostrils, and a lower craniofacial ratio, essentially how short and flat the muzzle is relative to the skull. The sobering part is that those three measurable factors explained only about a fifth of the variation in which dogs got sick and which didn't. Genetics and traits nobody has fully mapped yet appear to do most of the remaining work.
Breathing Isn't the Only Cost
BOAS gets most of the headlines, but it isn't the whole picture. The same flattened skull shape is linked to a higher rate of corneal ulcers and other eye injuries, since shallow eye sockets leave less protection. Skin folds trap moisture and bacteria, leading to recurring dermatitis in breeds like Bulldogs and Pugs. Brachycephalic puppies also tend to have proportionally large heads relative to their mothers' pelvises, so these breeds are delivered by cesarean section far more often than the average dog, in some studies the large majority of litters.
A Few Countries Are Stepping In
The popularity of these breeds hasn't gone unnoticed by regulators. In 2023, the Dutch government announced plans to prohibit breeding dogs and cats with the most extreme brachycephalic features, with the agriculture minister saying plainly that people shouldn't make animals suffer for the sake of looks. The Netherlands' kennel club has since stopped issuing pedigrees for Pugs and French Bulldogs bred to the traditional extreme standard. Norway went further: a court ruling found that breeding English Bulldogs and Cavalier King Charles Spaniels to their current standards violates the country's animal welfare law, putting breeders there at real legal risk. Nothing close to that exists in the United States, where French Bulldog litters remain in high demand and some breeders are working to select for wider nostrils and better airways instead of the flattest possible face.
If You Already Have One, or Want One
None of this means a flat-faced dog can't live a full, happy life, and plenty do. It does mean the responsibility for managing that risk sits mostly with the owner and the breeder. A few things genuinely help:
- Ask a breeder whether their dogs have been BOAS-graded by a vet, not just whether the parents "breathe fine."
- Keep your dog lean. Body condition score is one of the few risk factors researchers could actually measure, and it's the one you have the most control over.
- Watch for snoring that gets worse over time, exercise intolerance, or collapse after excitement, and bring it up with your vet rather than assuming it's just normal for the breed.
- Skip exercise during hot weather, since these dogs can't pant off excess body heat as efficiently as longer-nosed breeds.
The science here isn't a verdict on anyone who already loves one of these dogs. It's a reminder that a face bred to look a certain way can carry a real physical cost, and that cost is finally showing up in the data clearly enough that entire countries are rethinking the standard.