These Popular Flat-Faced Dogs Struggle To Breathe: Breeding Choices May Help

Bulldogs, French Bulldogs, and Pugs are popular breeds that can be seen all over social media feeds, in celebrity laps, and trotting through city parks. Their squashed faces and wide eyes are part of their appeal. But that same look can also make it harder for many of them to breathe. A new study confirms that the breathing problems plaguing these breeds are significantly inherited, and that smarter breeding choices could help turn that around.

Researchers publishing in PLOS ONE analyzed data from more than 4,000 UK Royal Kennel Club-registered dogs across all three breeds, examining results from a standardized breathing assessment run by The Royal Kennel Club. What they found gives veterinarians and breeders a science-backed reason for cautious optimism: a meaningful portion of each dog’s breathing ability is passed down from its parents, which means deliberate breeding choices could improve respiratory health in future litters.

That’s a significant development for a problem researchers have labeled a “brachycephalic crisis,” a term referring to the wave of health problems tied to short-skulled conformation.

Brachycephalic Obstructive Airway Syndrome, or BOAS, is no small matter. Noisy, labored breathing, gagging, overheating, and even collapse are among the symptoms, and in the most severe cases it can be fatal. Veterinarians increasingly view it as a serious welfare concern, even as many owners assume the heavy breathing is normal for the breed. Because testing is voluntary, the authors caution that the most severely affected dogs may be missing from the dataset, meaning the true rate of the disease could be higher than the data suggest.

A Breathing Test Is Grading Dogs Before They Breed

To measure respiratory health at scale, The Royal Kennel Club, in collaboration with the University of Cambridge, launched the Respiratory Function Grading Scheme, or RFGS, in 2019. Dogs go through a standardized exercise routine while an assessor listens to their breathing, then receives a grade from 0 to 3. Dogs graded 0 or 1 are considered clinically unaffected; those graded 2 or 3 have BOAS of increasing severity. The grading system had been validated against more sophisticated laboratory breathing measurements, confirming the exercise test reliably reflects what’s happening in a dog’s airways.

For this study, researchers from The Royal Kennel Club’s Health and Breeding Department and the University of Cambridge analyzed RFGS records from 1,474 Bulldogs, 1,917 French Bulldogs, and 900 Pugs in the UK RKC-registered population, alongside family tree records for each breed. By combining breathing grades with family history, they estimated how much variation in breathing health between individual dogs could be explained by genetics rather than environment or chance.

Heritability estimates in the main model ranged from 0.21 in Bulldogs to 0.45 in French Bulldogs, with Pugs at 0.28. Think of those figures as the share of breathing ability shaped by genetics rather than lifestyle or environment. Even at the lower end, that’s enough genetic signal for selective breeding to move the needle over generations. Researchers also found that nostril narrowing is similarly heritable, ranging from 0.31 to 0.39 across breeds, and is genetically linked to overall breathing function.

Obese Flat-Faced Dogs Face Nearly Four Times the Breathing Risk

One notable finding was just how much body weight amplifies the risk. Across all three breeds, obese dogs, those scoring 7 or above on a standard 9-point body fat scale, were nearly four times more likely to be clinically affected by BOAS than non-obese dogs. Pugs showed the steepest odds at 4.5 times higher risk and also had the highest obesity rate among the three breeds, at 16.8%.

Dogs with severely or moderately narrowed nostrils faced more than double the odds of being clinically affected by BOAS compared to dogs with open nostrils. In French Bulldogs, that figure was four times the odds. Only 6.2% of French Bulldogs in the study had fully open nostrils, despite the French Bulldog breed standard calling for “well-opened nostrils” since the early 1990s.

Most Flat-Faced Dogs Getting Tested Have Show-Breeding Backgrounds

Despite the scheme being active since 2019, participation rates remain low. The highest annual testing rate across the three breeds was just 3.1% of Pugs born in 2023. French Bulldogs and Bulldogs saw even lower rates, between 0.4% and 1.7%.

One notable gap: dogs connected to the competitive show world were far more likely to have been tested. Each step up in show-breeding background raised the odds of being tested by 71% in Bulldogs, 97.4% in French Bulldogs, and 85% in Pugs. Dogs bred in colors not recognized by official breed standards, a marker for dogs outside that community, were much less likely to have been tested and showed slightly worse breathing grades.

That matters because the surge in popularity of all three breeds has been driven largely by dogs outside traditional show communities. Non-standard-color dogs made up 56.1% of contemporary French Bulldogs and 32.6% of Bulldogs in the dataset, making them a major part of today’s breed landscape.

Crufts requirements are already changing. Starting in 2025, all three breeds entering the show must have completed RFGS testing, with the most severely graded dogs excluded. From 2026, dogs graded 2 or 3 will be ineligible to attend. But those rules only reach dogs already connected to the show world. For the many flat-faced dogs most in need of health screening, the science now clearly shows that better outcomes are possible in UK RKC-registered populations, if enough breeders choose to act on it.

---