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What Is BOAS (Brachycephalic Obstructive Airway Syndrome)?

What Is BOAS (Brachycephalic Obstructive Airway Syndrome)?

BOAS

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Owners

Learn what BOAS in dogs is, why flat-faced breeds like pugs and bulldogs struggle with it, symptoms to watch for, and treatment options.

By 

Sustainable Vet Group

Updated on

August 13, 2026

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This article is for informational purposes only and is not a substitute for professional veterinary advice. Every case is unique, so always consult your veterinarian for guidance specific to your pet.

This content is intended for veterinary professionals for educational purposes. It does not replace clinical judgment or tailored advice. Always rely on your training, expertise, and the specific context of your patients.

What Is BOAS (Brachycephalic Obstructive Airway Syndrome)?

If you own a Bulldog, Pug, French Bulldog, or Boston Terrier, you have probably heard your dog snore, snort, or struggle to catch their breath after a short walk.

Most owners assume it is just the breed. It is not.

That noisy breathing is a medical symptom. In many flat-faced dogs, it signals brachycephalic obstructive airway syndrome, a condition that affects the structure of the airway itself and worsens over time without treatment.

 

Quick answer: BOAS is a breathing disorder caused by the shortened skull structure of flat-faced dog breeds. It results in narrowed nostrils, an elongated soft palate, and other airway abnormalities that restrict airflow. BOAS is progressive, meaning it gets worse with age, and can lead to serious complications including heatstroke, collapse, and heart strain if left untreated.

 

Key takeaways

  • BOAS stands for brachycephalic obstructive airway syndrome: It is a set of structural airway abnormalities, not a single defect.
  • It is caused by selective breeding for flat faces: The skull shortens, but the soft tissue does not, creating crowding and obstruction.
  • BOAS is progressive: Signs that seem mild today will worsen over months and years without intervention.
  • Snoring and noisy breathing are symptoms, not quirks: Many owners normalize these signs and delay diagnosis.
  • Both surgery and lifestyle management are treatment options: Which is appropriate depends on the severity of the dog's airway obstruction.
  • Early diagnosis leads to significantly better outcomes: Dogs treated before age two tend to recover better from surgery.

What does brachycephalic mean?

The word brachycephalic comes from Greek: brachys (short) and kephale (head).

It describes dogs selectively bred for a flattened, wide skull. The facial bones shorten dramatically, but the soft tissue, including the soft palate, throat, and nasal passages, does not shrink proportionally.

The result is too much tissue crammed into too little space. Airflow is restricted at multiple points. The dog has to work much harder than a normal dog just to breathe.

What causes BOAS?

BOAS is a structural condition, not an infection or disease in the traditional sense.

It results directly from the anatomical changes that come with a shortened skull. These changes affect three main areas of the airway, each creating its own form of obstruction.

Stenotic nares

Stenotic nares are abnormally narrow nostrils.

A dog's primary airway for breathing is through the nose. When the nostrils are pinched or nearly closed, the dog cannot take in enough air through normal nasal breathing.

This forces them to breathe through the mouth, increases respiratory effort, and contributes to overheating because dogs rely on airflow through the nasal passages to regulate temperature.

Elongated soft palate

The soft palate is the flap of tissue at the back of the mouth that separates the nasal passages from the throat.

In brachycephalic dogs, the soft palate is often longer than the shortened skull can accommodate. It droops into the airway, partially blocking airflow with every breath.

This is one of the most common and significant components of BOAS. Dogs with a severely elongated soft palate often produce a loud snoring or rattling noise when breathing, even at rest.

Everted laryngeal saccules

Inside the larynx are small pouches called laryngeal saccules.

When a dog works harder to breathe, as BOAS dogs chronically do, increased negative pressure in the airway can pull these saccules outward into the airway. They then contribute directly to the obstruction.

Everted laryngeal saccules are considered a secondary change. They develop over time as a consequence of the breathing strain from the primary defects above.

Hypoplastic trachea

Some brachycephalic breeds, particularly English Bulldogs, also have a narrowed trachea (windpipe).

A hypoplastic trachea limits airflow further and is one of the more serious components of BOAS because it cannot be corrected surgically. It is also a significant risk factor for anesthetic complications.

Aberrant nasal turbinates

The turbinates are bony structures inside the nasal passages that normally direct airflow and warm incoming air.

In BOAS dogs, the turbinates sometimes grow abnormally and extend into regions where they obstruct airflow rather than helping it. This is increasingly recognized as an important contributor to nasal resistance in affected dogs.

How BOAS affects the body beyond breathing

BOAS does not only affect the airway. The constant effort of breathing against resistance puts strain on multiple body systems.

Secondary effects of BOAS include:

  • Gastrointestinal problems: Repeated swallowing of air, increased abdominal pressure, and esophageal dysfunction cause regurgitation, vomiting, and reflux in many BOAS dogs. Studies suggest a majority of severely affected dogs have concurrent GI issues.
  • Heart strain: Increased effort to breathe over time raises pressure in the chest. Research has documented right-sided cardiac changes in BOAS dogs, similar to patterns seen in humans with obstructive sleep apnea.
  • Poor sleep quality: Many BOAS dogs cannot enter deep sleep because their airway partially collapses when they relax. They wake repeatedly, leading to chronic sleep deprivation.
  • Overheating risk: Dogs cool themselves primarily through panting. When airflow is restricted, panting is less effective. BOAS dogs are at significantly higher risk of heatstroke in warm weather or after modest exercise.
  • Skin and eye problems: Excessive facial skin folds and prominent eyes in some brachycephalic breeds create additional health concerns alongside the airway issues.

Grading BOAS severity

Veterinarians use grading systems to assess how severely a dog's airway is affected. A common approach uses three or four grades:

GradeDescription
Grade 0No clinically significant breathing abnormality
Grade 1Mild: some noise, minimal exercise intolerance
Grade 2Moderate: noticeable breathing difficulty, exercise intolerance, possible sleep disruption
Grade 3Severe: significant respiratory distress at rest, high risk of collapse

 

Grading is typically done by a veterinarian after a physical examination and often a mild sedation assessment to evaluate the soft palate and laryngeal saccules directly.

Signs of BOAS to watch for

Many of the most significant signs of BOAS are normalized by owners of flat-faced breeds. Recognizing them as symptoms is the first step toward getting appropriate care.

Respiratory signs:

  • Noisy breathing at rest (snoring, snorting, rattling)
  • Labored breathing after minimal exertion
  • Open-mouth breathing when resting
  • Visible effort to inhale (neck extended, elbows out)
  • Coughing or gagging

Heat and exercise intolerance:

  • Rapid overheating during walks or play
  • Reluctance to exercise, even short distances
  • Excessive panting that does not resolve quickly

Gastrointestinal signs:

  • Frequent regurgitation or vomiting
  • Gulping and swallowing after eating

Sleep disturbances:

  • Restless sleep, frequent waking
  • Sleeping with the head propped up to keep the airway open

Emergency signs requiring immediate veterinary attention:

  • Blue or purple gums (cyanosis): indicates oxygen deprivation
  • Collapse or loss of consciousness
  • Severe open-mouth breathing with extreme distress

Is BOAS the same as normal breed breathing?

No. This is one of the most important misconceptions to address.

The snoring, snorting, and grunting sounds that many flat-faced breed owners accept as normal are actually signs of airway obstruction. Research suggests that approximately 60% of owners do not recognize these sounds as medical symptoms.

A dog breathing normally does not snore loudly at rest, overheat after a short walk, or struggle to sleep through the night. When these things happen routinely, they reflect structural obstruction that warrants veterinary assessment.

 

"Normal for the breed" does not mean healthy. BOAS is a welfare issue, and early recognition significantly changes the outcome.

 

Diagnosis

Diagnosis of BOAS involves several steps.

Physical examination: Your vet will observe your dog's breathing pattern, assess nostril size visually, and listen for airway sounds.

Sedated assessment: A definitive evaluation of the soft palate and laryngeal saccules often requires mild sedation, because dogs breathe differently when examined awake.

Imaging: Radiographs or CT scanning may be used to evaluate the trachea, lungs, and in some specialist settings, the nasal turbinates.

Respiratory function testing: Some specialist centers use whole-body barometric plethysmography, an objective tool that measures airflow restriction during normal breathing.

Many veterinarians recommend screening brachycephalic breeds as early as 6 to 12 months of age, before secondary changes like everted laryngeal saccules and laryngeal collapse develop.

Treatment overview

Treatment depends on the severity of the dog's airway obstruction and which components are present.

For mild cases: Lifestyle management including weight control, harness use, limiting exercise in heat, and avoiding stress can meaningfully reduce symptoms. For a detailed look at non-surgical management options for mild cases, including what these approaches involve and their limits, that guide covers conservative care in full.

For moderate to severe cases: Surgery to correct the primary defects, typically narrowed nostrils and elongated soft palate, is the most effective intervention. Understanding when BOAS requires surgical intervention and what the procedure involves helps you make an informed decision with your veterinarian.

Financial planning: For owners navigating the decision, a clear picture of the cost and risks of BOAS surgery is an important part of the planning process.

Prognosis

The outlook for dogs with BOAS depends heavily on when it is diagnosed and treated.

  • Dogs with mild to moderate BOAS treated early, typically before age two, tend to have significantly better outcomes.
  • Dogs with severe cases, particularly those that have developed laryngeal collapse (a tertiary complication of long-standing untreated BOAS), face a more guarded prognosis.
  • BOAS is a genetic condition. Dogs with significant airway problems should not be bred.

For understanding which dogs are at highest risk and what early signs to look for, the guide on breeds most commonly affected by BOAS covers breed-specific risk profiles in detail.

Frequently asked questions

Is BOAS painful for dogs?

Not in the way a wound is painful, but BOAS causes chronic discomfort and strain. Dogs with untreated BOAS experience constant respiratory effort, poor sleep, overheating, and sometimes gastrointestinal distress. The chronic oxygen restriction of severe BOAS significantly reduces quality of life.

Can BOAS be cured?

BOAS cannot be cured in the sense that the underlying brachycephalic conformation cannot be changed. However, surgery can significantly improve airflow by correcting the specific anatomical defects. Many dogs experience dramatic improvement in breathing quality and exercise tolerance after surgery.

Is it normal for my Pug or Bulldog to breathe noisily?

Noisy breathing in flat-faced breeds is extremely common, but it is not normal in the sense of being healthy. It indicates restricted airflow. How significant the restriction is varies by individual dog, which is why a veterinary assessment is the right next step when these sounds are present.

At what age should a brachycephalic dog be evaluated for BOAS?

Most veterinary guidelines recommend evaluation between 6 and 12 months of age. Early intervention, before secondary changes develop, leads to better surgical outcomes and a better long-term quality of life.

Does every flat-faced dog have BOAS?

Not every brachycephalic dog has clinically significant BOAS, but most have some degree of anatomical variation that creates breathing resistance. Some dogs have very mild cases that are manageable with lifestyle adjustments. Others require surgical correction to breathe comfortably.

BOAS is not a personality trait of flat-faced breeds. It is a structural medical condition that causes real discomfort and carries real health risks. Recognizing the signs, getting a veterinary assessment early, and understanding the treatment options are the most important things an owner of a brachycephalic dog can do. The earlier the diagnosis, the better the outcome.

Resources

The following sources were used as reference and background for this article:

  • PetMD. Brachycephalic Airway Syndrome in Dogs. petmd.com
  • VCA Animal Hospitals. Brachycephalic Airway Syndrome in Dogs. vcahospitals.com
  • Cornell University College of Veterinary Medicine. Brachycephalic Obstructive Airway Syndrome (BOAS). vet.cornell.edu
  • University of Florida College of Veterinary Medicine. Brachycephalic Obstructive Airway Syndrome (BOAS). smallanimal.vethospital.ufl.edu
  • Today's Veterinary Practice. An Overview of Brachycephalic Obstructive Airway Syndrome. todaysveterinarypractice.com
  • Liu, N.C. et al. (2017). Conformational risk factors of brachycephalic obstructive airway syndrome. PLOS ONE. ncbi.nlm.nih.gov

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