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  5. What is Brachycephalic Obstructive Airway Syndrome (BOAS)?

What is Brachycephalic Obstructive Airway Syndrome (BOAS)?

Brachycephalic dogs like this French Bulldog often suffer from brachycephalic obstructive airway disease (BOAS) which significantly reduces their quality of life.

Brachycephalic Obstructive Airway Syndrome (BOAS) is a breed-related disorder that means affected animals cannot breathe normally and this significantly compromises their welfare. Animals affected by brachycephaly (having a flat face) include dog breeds such as the French Bulldog, Pug, Boston Terrier, Boxer, British Bulldog, and Shih-tzu [1] and cats such as the Persian and Persian-derived breeds such as the Exotic Shorthair. Some rabbit breeds also suffer from brachycephaly, including the Netherland dwarf and the Lionhead breeds.

We know that the human families of brachycephalic or flat faced dogs, love and cherish these characterful and loving dogs. These breeds have great personalities and form strong bonds with their owners. Unfortunately, the exaggerated physical features that often initially draw people to these breeds, like their flat faces, cause these animals health and welfare problems. The noticeable breathing noises that these dogs make, like snuffling, snoring and snorting, is a sign that breathing is very difficult and distressing for the dog, and this realisation is heartbreaking.

Many brachycephalic animals have Brachycephalic Obstructive Airway Syndrome. BOAS is a lifelong, and often progressive disorder that affects an animal’s ability to breathe, exercise, eat, play, sleep, engage in normal behaviours and live comfortably. Extremely brachycephalic dogs have a shorter life span compared to dogs with less extreme brachycephaly or non-brachycephalic dogs [1].

Characteristics of brachycephalic animals

Brachycephalic animals have a shorter and wider skull than a non-brachycephalic dog, and their bottom jaw is disproportionately longer than their upper jaw. The soft tissue structures within the upper airways have not adapted structurally with the shortening of the skull, and therefore are squashed and packed within the smaller bony structures, and can block the airways [2, 3]. This conformation is a result of breeding to pedigree “breed standards”, where the focus has been on selecting for physical traits and appearance over traits that will maintain or improve the health and welfare of the animal.

Characteristics and consequences of Brachycephalic Obstructive Airway Syndrome (BOAS)

Airway abnormalities that characterise BOAS include narrowed nostrils, elongated soft palate, enlarged tongue, and reduced size of the windpipe [3]. Animals suffering from BOAS usually have more than one abnormality. Below is a brief explanation of each primary component of BOAS:

Narrowed nostrils (stenotic nares)

Malformation of the nostrils significantly narrows the opening of the nostrils. The opening of the nostrils may be so narrowed that they resemble a ‘slit’. This means that the airflow through the nostrils is greatly reduced, extra effort is needed to breathe normally, and dogs will need to adopt open-mouthed breathing when stressed, hot or excited. In more severe cases, some dogs rely on open-mouthed breathing all of the time. Please see this article for more information.

Elongated and thickened soft palate

The soft palate is a structure located at the back of the roof of the mouth. When it is too long and/or too thick, it partially covers the opening of the windpipe when the dog is taking a breath, reducing the amount of air that can be inhaled and causing snorting sounds. It is the most common abnormality in dogs with BOAS and is seen in over 85% of cases [4].

Enlarged tongue (macroglossia)

Many brachycephalic dogs have tongues that are too big compared to their mouths due to the changes of their skull from selective breeding for the flat-faced appearance. The enlarged tongue creates another obstructive barrier for airflow getting to the lungs, especially in dogs that rely on open-mouthed breathing. Some dogs need to stick out their tongues to try and improve their breathing.

Small windpipe (hypoplastic trachea)

The windpipe (trachea) does not develop properly and so less air enters the lungs, which can lead to animals struggling to take in more air with each breath.


BOAS often progressively worsens because the primary abnormalities can lead to the development of secondary changes [3]. For example, animals affected by BOAS have increased breathing effort and this can cause their airways to collapse, particularly the larynx (the cartilage flaps that sit at the entrance of the windpipe), and this can further obstruct airflow into the lungs. Some of the signs that animals show of having difficulty breathing such as using their abdominal muscles to breathe and producing noises during breathing are unfortunately misunderstand by some owners as being normal for the breeds (for examples of clinically affected dogs see here and here).

Animals with BOAS may also develop gastrointestinal problems resulting from their breathing difficulties; this may lead to gagging, regurgitation and vomiting [1, 5].

Signs of BOAS

Some signs you may see in animals with BOAS are [57]:

  • Increased effort during breathing
  • Noise during breathing (snoring sounds)
  • Coughing
  • Shortness of breath
  • Sleep apnoea or sleeping problems where dogs will frequently wake up during sleep or adopt an abnormal sleeping position (e.g., sleeping with a toy between their teeth) to avoid airway obstruction during sleep
  • Stress and an inability to exercise normally (called exercise intolerance)
  • Gastrointestinal disorders which are associated with vomiting, gagging, excessive salivation, regurgitation, and reflex
  • Sensitivity to heat including being prone to heat stroke; and
  • Sudden collapse

BOAS impairs an animal’s normal behaviour and their daily activities. Before acquiring, or if you own a brachycephalic animal, discuss with your veterinarian ways to manage this condition to ensure the best chance for your pet to live a healthy and comfortable life. Many animals with BOAS, particularly dogs, require surgical correction of their abnormalities and the younger they are treated, the fewer secondary changes will develop (giving a better chance for a reasonable quality of life); there are also fewer complications associated with surgery. It is advised to perform corrective airway surgery early (for example, between 6 and 12 months of age) as an elective procedure where possible to reduce the risk of post-operative complications and progression of their disease [7, 8].

If you have a brachycephalic animal, it is important that they have surgery if they need it, to give them the best chance for a comfortable life. However, even though many brachycephalic dogs can have their lives improved by surgery, it is not a ‘silver bullet’. Unfortunately, 60% of dogs still experience respiratory compromise even if they have had corrective surgery [7, 9]. In addition, there are increased risks with the sedation and anaesthesia of brachycephalic dogs regardless of whether they present for a BOAS-related surgery (e.g., stenotic nares, elongated soft palate) or unrelated surgery (e.g., caesarean, dental surgery) [10, 11]. It is important to discuss these risks with your veterinarian if you own a brachycephalic animal that needs surgery.

RSPCA and the Australian Veterinarian Association (AVA) believe that there needs to be a fundamental change in the way brachycephalic dogs are breed, to prioritise the dogs’ health and well-being over appearance. For more information see Love is Blind.

Brachycephalic animals and airline travel

BOAS is also thought to increase the risk of air travel for brachycephalic dogs. There have been a number of tragic fatal incidents when brachycephalic dogs have been transported by air, likely associated with Brachycephalic Obstructive Airway Syndrome (BOAS) [10]. This has resulted in many airlines refusing to accept these animals for air transport or imposing strict guidelines for airline travel due to the high risk of serious health problems and death.

RSPCA and the Australian Veterinarian Association (AVA) consider that transporting brachycephalic animals by air carries an unacceptable risk to the animal’s health and welfare. While animals who have BOAS are at greatest risk, BOAS may be present in many brachycephalic animals but not be diagnosed or recognised, and since so many brachycephalic animals are affected it is a significant risk to transport these animals. Therefore, while this risk is so high, we warn against transporting brachycephalic animals by air and advocate that owners of these animals avoid doing this in the interest of their pet’s safety and welfare.

Brachycephalic animals who are overweight, elderly, stressed, not accustomed to being in a crate or travelling and those who have other underlying medical conditions are at even greater risk.

More information

RSPCA Australia and the AVA are raising awareness to try to change how purebred dogs are selected and bred in Australia. Current and potential owners can play a vital role in helping to improve the welfare and lives of brachycephalic breeds. For more information or to get involved, visit the following websites: Love is Blind and the Australian Veterinary Association. See also: American College of Veterinary Surgeons, International Cat Care, Universities Federation for Animal Welfare and the UPEI Canine Inherited Disorders Database.


[1] O’Neill DG et al (2015) Epidemiological associations between brachycephaly and upper respiratory tract disorders in dogs attending veterinary practices in England. Canine Genetic Epidemiology 2: 10.

[2] Dupre G & Heidenreich D (2016) Brachycephalic syndrome. Veterinary Clinics of North America: Small Animal Practice 46(4): 691-707.

[3] Ekenstedt KJ et al (2020) Canine Brachycephaly: Anatomy, Pathology, Genetics and Welfare. Journal of comparative pathology 176: 109-115.

[4] Packer R and Tivers M (2015) Strategies for the management and prevention of conformation-related respiratory disorders in brachycephalic dogs. Veterinary Medicine: Research and Reports 6:219-232.

[5] Packer R et al (2015) Impact of facial conformation on canine health: brachycephalic obstructive airway syndrome. PLoS one 10 (10): e0137496.

[6] Meola S (2013) Brachycephalic Airway Syndrome. Topics in Companion Animal Medicine 28 (3): 91-96.

[7] Moses, P (2016) Advice from a specialist surgeon. Accessed 3.2.2020.

[8] Lindsay B et al (2020), Brachycephalic airway syndrome: management of post-operative respiratory complications in 248 dogs. Australian Veterinary Journal, 98: 173-180.

[9] Liu N et al (2017) Outcomes and prognostic factors of surgical treatments for brachycephalic obstructive airway syndrome in 3 breeds. Veterinary Surgery 46(2): 271-280.

[10] Fawcett A et al (2019) Consequences and management of canine brachycephaly in veterinary practice: perspectives from Australian veterinarians and veterinary specialists. Animals 9 (1).

[11] U.S. Department of transportation (2010) “Short-faced” dogs more prone to death in flight, according to DOT data (accessed on June 24, 2021)

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Updated on August 9, 2021
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