Which Flat-Faced Dog Breeds Have the Worst Breathing Problems? The 2026 PLOS Study

If your dog snores loudly, snorts after a short walk, or struggles in summer heat, a new 2026 PLOS ONE study has answers — and a warning. Researchers screened more than 1,500 short-skulled (brachycephalic) dogs across 14 breeds and found that the risk of Brachycephalic Obstructive Airway Syndrome (BOAS) varies dramatically from breed to breed.

What is BOAS, exactly?

BOAS stands for Brachycephalic Obstructive Airway Syndrome. In flat-faced breeds, a shortened skull squeezes normal airway tissue into a smaller space — narrowing nostrils, creating a long soft palate, and causing a collapse of the voice box over time. The result: noisy breathing, exercise intolerance, regurgitation, sleep disruption, and in serious cases, life-threatening overheating.

Until now, owners and vets have largely lumped all flat-faced breeds together. The 2026 PLOS study changes that.

What the 2026 study did

A team led by researchers in the UK and US screened 1,517 dogs across 14 brachycephalic breeds using a standardized exercise tolerance test plus a clinical airway exam. Each dog was graded BOAS-free, mildly affected, moderately affected, or severely affected.

They also recorded body condition, neck girth, nostril shape, and skull index — letting them tease apart breed risk from how an individual dog is built.

The breeds most at risk

Three breeds stood out as the highest-risk group:

1. French Bulldog — roughly half of dogs tested showed clinically significant BOAS.
2. English Bulldog — similar prevalence, with collapsing nostrils a frequent driver.
3. Pug — high overall risk, especially in dogs with a heavier build.

Moderate-risk breeds included the Boston Terrier, Boxer, Cavalier King Charles Spaniel, and Shih Tzu. Lower-risk (but not risk-free) breeds were the Affenpinscher, Brussels Griffon, Pekingese, Lhasa Apso, Japanese Chin, and King Charles Spaniel.

If you own a small flat-faced breed, you may also want to read our companion piece on common health risks in small breeds and why ear disease is so common in small dogs.

What actually predicts BOAS in your dog

The study's most useful finding for owners isn't the breed list — it's the individual risk factors that turned a low-risk dog into a high-risk one:

• Pinched (stenotic) nostrils were the single strongest predictor.
• Higher body condition score (extra weight) sharply raised risk in every breed.
• Thicker neck girth correlated with worse exercise tolerance.
• Shorter muzzle relative to skull length increased risk independent of breed.

Translation: a leaner Frenchie with open nostrils may breathe better than an overweight Boston Terrier. Conformation matters more than breed name.

What owners should do this week

The authors recommend a practical, four-step plan:

1. Ask your vet for a BOAS functional grade. A 3-minute trot test plus airway exam takes one appointment.
2. Keep your dog lean. Even a 10% weight loss can move a moderate dog into the mild category.
3. Avoid heat and humidity. Walk early or late; never leave a flat-faced dog in a warm car, even briefly.
4. Use a harness, not a collar. Pressure on the trachea worsens an already crowded airway.

For severely affected dogs, surgical correction (widening nostrils, shortening the soft palate) can be life-changing — and the study confirms outcomes are best when surgery happens before secondary airway collapse develops.

Puppy buyers: what to ask before you commit

If you're considering a flat-faced puppy, the study's data offers a buyer's checklist:

• Ask the breeder if both parents have a documented BOAS functional grade.
• Look for open, round nostrils in the puppy — not pinched slits.
• Prefer puppies with slightly longer muzzles within the breed standard.
• Avoid lines marketed as "extreme," "exotic," or "micro" — these typically have shorter skulls and worse airways.

Early-life decisions matter beyond breathing, too. Our guide to the 3–16 week socialization window and the latest evidence on reward-based training covers what to do in those crucial first months.

The bigger picture

Brachycephalic breeds remain among the most popular dogs in the US, UK, and across Europe — and demand keeps climbing. The 2026 PLOS team is direct: the only durable fix is breeding for moderation — slightly longer muzzles, open nostrils, and leaner builds — alongside owner education and accessible BOAS screening.

If you love a Frenchie, Pug, or Bulldog (and millions of us do), the message isn't to panic. It's to measure, manage, and breed smarter so the next generation of flat-faced dogs can simply breathe.

For more on how breed shapes daily life and health, see our deep dives on why small dogs shouldn't jump off the couch and what Golden Retriever genes reveal about behavior.