What is BOAS in French Bulldogs?

BOAS stands for Brachycephalic Obstructive Airway Syndrome. It is the collective term for the anatomical features of flat-faced dogs that restrict airflow through the nose and throat. In French Bulldogs, the most significant features are stenotic nares (narrowed nostrils), an elongated soft palate that partially blocks the airway, and, in more severe cases, everted laryngeal saccules and a narrowed trachea. The combination of these features means BOAS-affected dogs have to work harder to breathe than dogs with normal nasal anatomy.

How do I know if my French Bulldog has BOAS?

Many French Bulldogs have some degree of BOAS without it being severely debilitating, which makes recognition difficult. Signs that suggest significant BOAS include: loud, laboured breathing at rest; open-mouth breathing during normal activity (not just after exercise or in heat); exercise intolerance (tiring quickly on short walks); sleep disturbance; coughing or retching; gagging; and in severe cases, cyanosis (blue tinge to the gums) or fainting. If you are uncertain, a functional breathing assessment with a BOAS-trained vet is the most reliable way to evaluate your dog.

What is the BOAS grading scale?

The KC/Cambridge University BOAS grading scale runs from Grade 0 (clinically unaffected) to Grade 3 (severely affected). Grade 0 dogs have normal or near-normal airway function. Grade 1 dogs have mild but clinically acceptable symptoms. Grade 2 dogs have moderate symptoms that significantly affect quality of life and are not suitable for breeding. Grade 3 dogs have severe symptoms requiring treatment. Only dogs with Grade 0 or 1 should be used in breeding programmes, according to KC guidelines.

Can BOAS be treated without surgery?

Mild BOAS (Grade 1 and some Grade 2) can be managed conservatively: keeping the dog at a healthy weight, avoiding heat and strenuous exercise, using a harness instead of a collar, and monitoring for deterioration. Weight management is particularly important because excess weight around the chest and throat makes BOAS symptoms significantly worse. However, dogs with Grade 2 or 3 BOAS generally benefit from surgical correction, and conservative management alone is insufficient for moderate to severe cases.

At what age is BOAS surgery usually performed in French Bulldogs?

BOAS surgery is typically performed once a dog is fully grown, usually from 12 months onwards. Some vets recommend intervention earlier if symptoms are severe. Surgery is commonly combined with neutering to reduce the number of anaesthetic events the dog undergoes. The procedure is most effective when performed before secondary changes (such as everted laryngeal saccules and laryngeal collapse) have developed, which argues for earlier assessment and intervention rather than watchful waiting.

How much does BOAS surgery cost in the UK?

BOAS surgery costs in the UK typically range from £1,500 to £4,000 depending on the complexity of the procedure, the facilities required and whether specialist referral is involved. The most commonly performed procedure (nares widening combined with soft palate resection) at a general practice typically costs £1,500 to £2,500. Referral to a specialist in veterinary surgery adds to the cost but often improves outcomes for more complex cases. See the dedicated BOAS surgery cost guide for a detailed breakdown.

Health

BOAS in French Bulldogs: Breathing Problems Explained

Last reviewed: June 2026

Close-up of a French Bulldog's face showing the flat muzzle and nostril structure

Contents

Breathing difficulties are the most significant single health concern in the French Bulldog breed. BOAS, Brachycephalic Obstructive Airway Syndrome, describes the cluster of anatomical features that restrict airflow in flat-faced dogs, and it affects the majority of French Bulldogs to some degree. Understanding what it is, what it looks like and what can be done about it is fundamental to responsible Frenchie ownership.

This guide covers the anatomy behind BOAS, the grading system used to assess severity, the signs that indicate a dog’s breathing needs attention, and what treatment looks like. For surgery costs specifically, see the BOAS surgery cost guide.

The anatomy of BOAS

The French Bulldog’s flat face is the result of selective breeding for a compressed skull structure. That same compression affects the airways in ways that create breathing resistance.

Stenotic nares

The nostrils (nares) of many French Bulldogs are narrower than those of dogs with normal nasal anatomy. Narrowed nostrils mean less air can enter the nose with each breath, increasing the work required to breathe through the nose. In dogs with very tight stenotic nares, the nostrils may appear to collapse partially inward with each inhalation.

Stenotic nares are one of the most easily addressed BOAS features surgically, and are often the first procedure performed when intervention is recommended.

Elongated soft palate

The soft palate is the soft tissue at the back of the roof of the mouth that separates the nasal passage from the throat. In brachycephalic dogs, the soft palate is often longer than the compressed skull can accommodate, causing it to extend into the throat and partially obstruct the airway during breathing and swallowing.

The elongated soft palate is responsible for much of the characteristic snoring in French Bulldogs, and in moderate to severe cases creates significant breathing resistance. Surgical resection of the excess soft palate tissue is the cornerstone of BOAS surgery.

Everted laryngeal saccules

The laryngeal saccules are small pouches just inside the entrance to the larynx (voicebox). In dogs with obstructed airways, the increased negative pressure created by working harder to breathe can cause these saccules to be sucked outward (everted), further reducing the airway space. Everted saccules are typically a secondary development in dogs with significant untreated BOAS rather than a primary feature.

Hypoplastic (narrow) trachea

Some French Bulldogs have a trachea (windpipe) that is narrower than normal for their body size. This is a structural feature that cannot be corrected surgically (unlike the other three components of BOAS) and sets an upper limit on how much airway function can be improved through surgery. Tracheal diameter can be assessed radiographically.

Laryngeal collapse

In the most severe cases, the cartilages of the larynx itself can collapse due to the sustained negative pressure of BOAS, further obstructing the airway. Laryngeal collapse represents advanced, long-standing BOAS and is a strong argument for earlier intervention rather than later.

The BOAS grading system

The KC and Cambridge University Veterinary School developed a grading system for BOAS in French Bulldogs based on functional breathing assessment. A trained vet assesses the dog during exercise (typically a brief treadmill test or controlled walk) and at rest to evaluate how hard the dog is working to breathe. The grades are:

Grade 0: Clinically unaffected. Normal or near-normal breathing with no significant obstruction.

Grade 1: Mildly affected. Some noise and increased effort but within acceptable limits. These dogs can have full lives without surgery, though monitoring is important.

Grade 2: Moderately affected. Significant obstruction affecting quality of life. Dogs at this grade typically benefit from surgical intervention. Grade 2 dogs should not be used for breeding.

Grade 3: Severely affected. Exercise intolerance, open-mouth breathing at rest, significant distress. Surgical intervention is strongly indicated.

The grading scheme was developed primarily for assessing breeding dogs, but it is also clinically useful for guiding treatment decisions in any French Bulldog.

Recognising significant BOAS

Most Frenchies make some noise when they breathe. The challenge for owners is distinguishing the normal sounds of a brachycephalic dog from sounds that indicate clinically significant obstruction.

Signs that suggest significant BOAS and warrant veterinary assessment:

Loud, laboured breathing at rest (not just after exercise)
Open-mouth breathing during normal, calm activity
Exercise intolerance: the dog becomes distressed or gives up quickly on short walks
Frequent coughing or retching, particularly after excitement or exertion
Disturbed sleep: the dog wakes itself up, sleeps in unusual positions to keep the airway open
Gagging or regurgitation (which can also be related to BOAS-associated gastrointestinal problems)
Cyanosis: a blue or grey tinge to the gums during or after exercise, indicating dangerously low oxygen

If your Frenchie shows any of the last two signs, contact a vet immediately. Cyanosis is a medical emergency.

BOAS assessment

A proper BOAS assessment involves a functional evaluation, not just observation of the dog at rest. The Cambridge grading protocol involves a short period of controlled exercise followed by resting observation, measuring the dog’s recovery time and breathing pattern. This is different from a standard vet check and is specifically required for dogs entering the KC health scheme.

When consulting a vet about your Frenchie’s breathing, asking specifically for a BOAS functional assessment is more informative than a routine listen to the chest.

Treatment

Conservative management

For Grade 0 and Grade 1 dogs, conservative management is appropriate:

Weight management. Obesity makes BOAS dramatically worse. Even small amounts of excess weight around the chest and throat increase breathing resistance. Keeping a BOAS-affected dog lean is one of the highest-impact interventions available without surgery.
Avoiding heat. High temperatures increase breathing demand exactly when BOAS limits oxygen delivery. French Bulldogs should not be exercised in temperatures above about 20°C, and should have access to cool, air-conditioned environments in summer.
Harness rather than collar. Neck pressure from a collar increases BOAS symptoms significantly. A correctly fitted Y-shaped harness distributes pressure across the chest.
Avoiding excitement and stress. Situations that cause panting or hyperventilation increase BOAS risk.

Surgery

For Grade 2 and 3 dogs, and for Grade 1 dogs where quality of life is affected, surgery is the most effective treatment. Standard BOAS surgery involves one or more of:

Rhinoplasty (nares widening): A small amount of tissue is removed from the nostrils to widen the openings. The procedure is relatively quick and recovery is straightforward. Results are immediate.

Soft palate resection (staphylectomy or folded flap palatoplasty): Excess soft palate tissue is removed to reduce obstruction at the back of the throat. Modern techniques (including the folded flap palatoplasty) provide better, more lasting results than older resection methods.

Lateral saccule resection: Everted laryngeal saccules are removed if present. Typically performed at the same time as soft palate surgery.

These procedures are often performed together in a single anaesthetic event to reduce the number of times the dog undergoes anaesthesia.

Outcomes are generally good when surgery is performed before secondary changes develop. Most dogs show significant improvement in exercise tolerance and a reduction in breathing noise. The earlier surgery is performed (before laryngeal saccule eversion and tracheal changes become significant), the better the prognosis.

BOAS and insurance

Given the prevalence of BOAS in the breed and the costs of assessment and surgery, pet insurance is essential. Starting insurance before any BOAS-related symptoms present or before any vet note on the record is the best way to ensure the condition is covered. Once a vet has noted breathing difficulties on a dog’s record, BOAS may be recorded as a pre-existing condition by new insurers. The insurance guide covers what to look for in a policy for this breed specifically.

BOAS and responsible breeding

The KC’s requirement that Assured Breeders have both parents BOAS-graded at 0 or 1 before breeding is a direct response to the prevalence of the condition. Dogs at Grade 2 or 3 should not be producing offspring who inherit the same degree of obstruction.

When buying a French Bulldog puppy, asking for the BOAS grade of both parents, as a specific Grade 0 or 1 certificate rather than a general claim of “health tested,” is one of the most important questions you can ask. The buying guide covers this and all other health documentation to request.

BOAS has a direct effect on sleep quality, as restricted airflow can cause hypoxic episodes during sleep. The sleep guide explains what normal and abnormal sleep looks like for the breed, including the signs that warrant a vet check. Because BOAS affects heat tolerance and overall health burden, its relationship to longevity is discussed in the French Bulldog lifespan guide. For equipment, the best harness for French Bulldogs guide explains in detail why collar pressure directly worsens BOAS and what to look for when choosing a harness for a brachycephalic dog. On neutering, the considerations specific to dogs with compromised airways, including whether to combine the procedure with BOAS surgery, are in the neutering a French Bulldog guide. On sleep, the characteristic snoring and snuffling sounds of the breed, and how to tell normal breed-level noise from signs that warrant a BOAS assessment, are covered in the French Bulldog snoring guide. For the specific question of air travel, most airlines restrict or outright ban brachycephalic breeds in cargo due to respiratory risk; the flying with a French Bulldog guide covers the current UK airline policies and the safer alternatives. For the related pattern of reverse sneezing, the rapid inward honking reflex that shares the same anatomical background as BOAS and is far more common in brachycephalic breeds, the reverse sneezing guide explains what triggers it and when it warrants veterinary attention.

Frequently asked questions

: BOAS stands for Brachycephalic Obstructive Airway Syndrome. It is the collective term for the anatomical features of flat-faced dogs that restrict airflow through the nose and throat. In French Bulldogs, the most significant features are stenotic nares (narrowed nostrils), an elongated soft palate that partially blocks the airway, and, in more severe cases, everted laryngeal saccules and a narrowed trachea. The combination of these features means BOAS-affected dogs have to work harder to breathe than dogs with normal nasal anatomy.
: Many French Bulldogs have some degree of BOAS without it being severely debilitating, which makes recognition difficult. Signs that suggest significant BOAS include: loud, laboured breathing at rest; open-mouth breathing during normal activity (not just after exercise or in heat); exercise intolerance (tiring quickly on short walks); sleep disturbance; coughing or retching; gagging; and in severe cases, cyanosis (blue tinge to the gums) or fainting. If you are uncertain, a functional breathing assessment with a BOAS-trained vet is the most reliable way to evaluate your dog.
: The KC/Cambridge University BOAS grading scale runs from Grade 0 (clinically unaffected) to Grade 3 (severely affected). Grade 0 dogs have normal or near-normal airway function. Grade 1 dogs have mild but clinically acceptable symptoms. Grade 2 dogs have moderate symptoms that significantly affect quality of life and are not suitable for breeding. Grade 3 dogs have severe symptoms requiring treatment. Only dogs with Grade 0 or 1 should be used in breeding programmes, according to KC guidelines.
: Mild BOAS (Grade 1 and some Grade 2) can be managed conservatively: keeping the dog at a healthy weight, avoiding heat and strenuous exercise, using a harness instead of a collar, and monitoring for deterioration. Weight management is particularly important because excess weight around the chest and throat makes BOAS symptoms significantly worse. However, dogs with Grade 2 or 3 BOAS generally benefit from surgical correction, and conservative management alone is insufficient for moderate to severe cases.
: BOAS surgery is typically performed once a dog is fully grown, usually from 12 months onwards. Some vets recommend intervention earlier if symptoms are severe. Surgery is commonly combined with neutering to reduce the number of anaesthetic events the dog undergoes. The procedure is most effective when performed before secondary changes (such as everted laryngeal saccules and laryngeal collapse) have developed, which argues for earlier assessment and intervention rather than watchful waiting.
: BOAS surgery costs in the UK typically range from £1,500 to £4,000 depending on the complexity of the procedure, the facilities required and whether specialist referral is involved. The most commonly performed procedure (nares widening combined with soft palate resection) at a general practice typically costs £1,500 to £2,500. Referral to a specialist in veterinary surgery adds to the cost but often improves outcomes for more complex cases. See the dedicated BOAS surgery cost guide for a detailed breakdown.