Study Finds Breathing Problems Widespread Across 14 Flat-Faced Dog Breeds

That snorting, wheezing sound from a Pekingese or Shih Tzu might seem like part of the breed’s charm. Veterinarians have a different word for it: a symptom.

New research from the University of Cambridge confirms that the breathing crisis long associated with French Bulldogs, Pugs, and Bulldogs runs much deeper through the world of flat-faced dogs than most owners know. Researchers tested 898 dogs across 14 breeds and found that in nearly every breed, some level of breathing abnormality was present. For two breeds, the Pekingese and the Japanese Chin, the disease rates were just as bad as the breeds already notorious for the problem.

The findings, published in PLOS One, arrive at a moment when flat-faced breeds are more popular than ever. And the more people buy dogs for their smushed, wide-eyed looks, the more dogs end up paying the price.

Why Flat-Faced Dogs Struggle to Breathe

Brachycephalic Obstructive Airway Syndrome, or BOAS, is what happens when a dog’s skull has been bred into a shape the airway inside cannot accommodate. Nostrils become too narrow. Soft tissue crowds the throat. The dog works harder and harder just to pull in air, and that chronic strain causes further damage over time.

It goes well beyond snoring. Dogs with BOAS can’t exercise normally, overheat easily, and sleep poorly. In severe cases they turn bluish from oxygen deprivation and risk collapse. Most owners never connect those dots because the sounds have been normalized as a breed trait, which researchers say is one of the biggest reasons the problem keeps getting worse.

Flat-faced breeds have surged in popularity over the past two decades, fueled by social media and the simple truth that a lot of people find that squashed, baby-faced look irresistible. But selecting generation after generation for shorter skulls compresses the anatomy those dogs need to breathe. The face gets flatter. The airway doesn’t grow with it.

Which Breeds Are Struggling Most

Between 2021 and 2024, Cambridge researchers evaluated 898 dogs at a veterinary hospital and at dog shows and health testing events across the UK. Each dog went through a standardized breathing assessment, including a three-minute exercise test, and was scored on a scale from 0 (no problem) to 3 (severe distress). Scores of 2 or 3 are considered clinically significant, meaning the breathing problem is serious enough to affect daily life.

The Pekingese and Japanese Chin came out as the highest-risk breeds. Only 10.9% of Pekingese and 17.4% of Japanese Chin dogs scored a clean Grade 0, putting them in the same territory as Pugs, French Bulldogs, and Bulldogs, where healthy scores hover around 7% to 11%. The Griffon Bruxellois, Boston Terrier, King Charles Spaniel, Dogue de Bordeaux, and Shih Tzu all fell into a moderate-risk category, with at least half of each breed showing some level of disease. The Staffordshire Bull Terrier, Cavalier King Charles Spaniel, Chihuahua, Boxer, and Affenpinscher fared considerably better. The Pomeranian and Maltese stood out as the healthiest, with no dogs in either breed reaching clinically significant scores, though both had relatively small sample sizes.

One result genuinely surprised the researchers. The King Charles Spaniel has one of the flattest faces in the entire study, yet 40% of those dogs tested clean. That’s a far better outcome than the Pekingese or Japanese Chin, which share similarly extreme facial structure. As the authors put it, “the assumption that the degree of facial hypoplasia is the primary cause of BOAS is likely an oversimplification.”

A flat face raises the risk, but it doesn’t tell the whole story. Something else is going on inside those dogs, whether in their genetics, the specific shape of their internal airways, or factors researchers haven’t fully mapped yet.

What Owners Can Actually Do

Across all 14 breeds, three factors consistently linked to worse breathing emerged: a flatter face, narrower nostrils, and being overweight. Together they explained only about 20% of the variation in outcomes, meaning the rest likely comes down to genetics and internal anatomy that no physical measurement can fully capture.

The weight finding is the one owners can act on right away. Overweight dogs were 1.8 times more likely to have BOAS than dogs at a healthy weight, a pattern that held across multiple breeds. For Shih Tzu, Cavalier King Charles Spaniel, and Affenpinscher owners in particular, keeping a dog lean is one of the most practical ways to ease breathing risk. It won’t fix the underlying anatomy, but the data suggest it makes a meaningful difference.

Nostril shape mattered too. Among the highest-risk breeds, very few dogs had fully open nostrils: only 5.8% of Japanese Chin and 17.8% of Pekingese. Breeds with more open nostrils tended to breathe better overall, and in Boston Terriers, nostril width was a significant predictor of disease on its own. Surgical widening of the nostrils is commonly used in clinical practice for affected dogs, and these findings reinforce why it helps.

Britain’s official respiratory health screening program currently covers only French Bulldogs, Bulldogs, and Pugs. Researchers are calling for that to expand, arguing that breeds in the moderate and high risk categories have the most to gain from formal screening that gives breeders real data to work with. Prospective buyers can also do their homework before choosing a dog by asking breeders for respiratory grading results and looking for animals with more open nostrils.

For owners of Pekingese and Japanese Chin who’ve spent years calling that wheeze adorable, the message here is plain: it isn’t a quirk. It’s the dog telling you something is wrong.

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Medical Disclaimer: This article is based on a single observational study and is intended for informational purposes only. It does not constitute veterinary advice. If you have concerns about your dog’s breathing or overall health, consult a licensed veterinarian.

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