BOAS, or brachycephalic obstructive airway syndrome, is a condition where a dog’s shortened skull creates physical blockages in the airways that make breathing difficult. It affects flat-faced breeds like French Bulldogs, Pugs, and English Bulldogs most severely, but it can occur in over a dozen short-nosed breeds to varying degrees. The core problem is structural: the soft tissue inside these dogs’ heads hasn’t shrunk to match their compacted skulls, so there’s too much tissue crammed into too small a space.
The Four Airway Problems Behind BOAS
BOAS isn’t a single defect. It’s a combination of up to four anatomical abnormalities, and a dog can have one or all of them.
- Stenotic nares: Abnormally narrow nostrils that may collapse inward when the dog inhales, restricting airflow before it even enters the nose.
- Elongated soft palate: The soft tissue at the back of the mouth extends too far and partially blocks the opening to the windpipe.
- Everted laryngeal saccules: Small pockets of tissue near the vocal cords get sucked inward during breathing, further narrowing the airway. This tends to develop over time as a secondary problem caused by the chronic effort of pulling air past other obstructions.
- Hypoplastic trachea: A windpipe that is proportionally too narrow for the dog’s body size. This is especially common in Bulldogs.
The first two problems are present from birth. The everted saccules often develop later because of the increased negative pressure created each time the dog struggles to inhale. Think of it like sucking hard through a narrow straw: the force pulls nearby tissue into the airway, making the obstruction progressively worse.
Which Breeds Are Most At Risk
French Bulldogs, Pugs, and English Bulldogs get the most attention, and for good reason. They’re the breeds with the highest rates of clinically significant disease and are the focus of most screening programs worldwide. But a large cross-sectional study across 14 brachycephalic breeds found that Pekingese and Japanese Chin actually had the highest rates of BOAS, with only about 11% and 17% of tested dogs being completely free of respiratory signs.
Several breeds fall into a moderate risk category, where 25 to 50% of dogs tested completely clear. These include the Brussels Griffon, Boston Terrier, Dogue de Bordeaux, King Charles Spaniel, and Shih Tzu. Breeds like Cavalier King Charles Spaniels, Boxers, Chihuahuas, Staffordshire Bull Terriers, Affenpinschers, and Pomeranians had lower risk, with at least half testing clear and at least 75% showing no clinically significant disease. Only Maltese and Pomeranians had zero dogs with clinically significant breathing problems in the study sample.
The pattern isn’t identical across breeds either. Pugs are particularly prone to laryngeal collapse and tend to produce a high-pitched wheezing sound called stridor. Bulldogs, on the other hand, are more likely to have a hypoplastic trachea. Researchers have also identified a genetic mutation linked to BOAS that appears common in Bulldogs and French Bulldogs specifically.
Signs You Might Notice
The hallmark sounds of BOAS are loud snoring, snorting, and noisy breathing, even at rest. Many owners assume these are just “normal breed sounds,” but they’re actually signs of partially obstructed airways. Other common signs include exercise intolerance (tiring quickly on walks, reluctance to play), gagging or retching, and episodes where the dog seems to struggle for air, especially in warm or humid weather. Some dogs sleep with their heads elevated or a toy propped under their chin because lying flat worsens the obstruction.
Heat is a particular danger. Dogs cool themselves primarily by panting, which requires moving large volumes of air through the airways. A dog with BOAS can’t do this efficiently, making them far more vulnerable to heatstroke than other breeds.
The Digestive Problems That Come With It
BOAS doesn’t just affect breathing. In one study of 30 brachycephalic dogs with the syndrome, 77% also had digestive symptoms like vomiting, regurgitation, or excessive drooling. This connection isn’t a coincidence. The same increased negative pressure in the chest that pulls laryngeal tissue into the airway also affects the digestive tract. It can promote gastroesophageal reflux (stomach acid flowing back into the esophagus) and hiatal hernia, where part of the stomach pushes up through the diaphragm. Brachycephalic breeds also tend to have anatomical quirks in their esophagus that compound the problem.
If your flat-faced dog frequently vomits, gags after eating, or regurgitates undigested food, these symptoms may be directly connected to their breathing issues rather than a separate stomach problem.
How BOAS Is Graded
Veterinarians and breed health programs use a standardized Respiratory Function Grading Scheme developed at the University of Cambridge. It assigns dogs one of four grades after a short exercise test:
- Grade 0: No respiratory signs. The dog is clinically unaffected.
- Grade 1: Some respiratory noise is present, but it doesn’t affect exercise performance. Still considered clinically unaffected.
- Grade 2: Moderate signs of BOAS that should be monitored and may need treatment.
- Grade 3: Severe signs requiring veterinary examination and treatment. Dogs at this grade should not be bred.
This grading system is now used internationally. As of April 2026, the Orthopedic Foundation for Animals in the U.S. expanded the list of breeds eligible for official certification to include 14 brachycephalic breeds beyond the original three, covering everything from Affenpinschers to Staffordshire Bull Terriers. The goal is to give breeders a standardized tool for selecting dogs with better airway function, though BOAS inheritance is complex and not entirely predictable even when both parents grade well.
Surgical Treatment and What to Expect
For dogs with Grade 2 or 3 BOAS, surgery is the primary treatment. The two most common procedures address the two most fixable problems: widening the nostrils and shortening the soft palate. Nostril widening involves removing a small wedge of tissue from each nostril and suturing it closed, creating a wider opening for air. Soft palate surgery trims excess tissue so it no longer dangles into the airway.
In a study of 423 dogs that underwent both procedures, 72.6% showed measurable improvement in their breathing after surgery. About 34% also saw improvement in their digestive symptoms, reinforcing the link between airway pressure and GI problems. Surgery tends to be most effective when performed earlier, before the chronic strain on the airway causes secondary changes like laryngeal collapse that are harder to reverse.
Recovery typically involves a short hospital stay for monitoring, since post-surgical swelling in the airway can temporarily worsen breathing. Most dogs go home within a day or two. The improvement isn’t always dramatic overnight. Swelling takes time to resolve, and some dogs need a few weeks before the full benefit is clear. Surgery doesn’t create a normal airway, but it can significantly reduce the effort a dog needs to breathe comfortably.
Managing BOAS Without Surgery
For dogs with milder signs (Grade 1 or early Grade 2), or as a complement to surgery, lifestyle management makes a real difference. Keeping your dog at a lean body weight is one of the most impactful things you can do, since extra fat around the neck and chest further compresses already-narrow airways. Use a harness instead of a collar to avoid putting pressure on the throat. Limit exercise in hot or humid weather, and keep walks shorter during summer months. Air conditioning isn’t a luxury for these breeds; it’s a safety measure.
Slow-feeder bowls can help with the digestive component by reducing how much air a dog swallows during meals. Elevated food bowls and smaller, more frequent meals may also reduce regurgitation in dogs with reflux symptoms.