What is BOAS?
Updated By PetymFacts checked against official sources on
Quick answer
BOAS, brachycephalic obstructive airway syndrome, is a breathing disorder of flat-faced dogs. Narrow nostrils, an overlong soft palate and a small windpipe block airflow, so affected dogs snore, snort, tire quickly and overheat easily. It is worse in heat, humidity and obesity. Surgery can widen the airway, and a lean weight helps.
Also called brachycephalic obstructive airway syndrome, brachycephalic airway syndrome, snoring pug, flat-faced dog breathing problems.
Key facts
- Breeds most affected include the French Bulldog, Bulldog, Pug, Pekingese, Shih Tzu, Japanese Chin, Boxer and Boston Terrier. University of Cambridge Department of Veterinary Medicine
- The airway can be blocked by narrowed nostrils, a soft palate too long for the mouth, everted laryngeal saccules and a narrow windpipe. VCA Animal Hospitals
- BOAS risk rises sharply as the muzzle shortens; in one study it occurred only in dogs whose muzzle was less than half the length of the skull, and thicker necks and obesity raised the risk further. PLOS ONE (2015)study
- Signs are often worse in hot or humid weather, and obesity worsens them. VCA Animal Hospitals
- Flat-faced dogs had about twice the odds of heat-related illness in a large UK study. Scientific Reports (2020)study
- Dogs under two years old at surgery have a better outlook afterwards. VCA Animal Hospitals
What are the signs of BOAS?
Many owners think snoring and snorting are just how the breed sounds. They are the mildest signs of a blocked airway.
Mild BOAS shows as noisy breathing during exercise, snorting when excited and snoring when relaxed or asleep. More affected dogs tire quickly, struggle to cool down, and may retch, regurgitate or eat poorly. Severe cases collapse or faint after exercise or excitement. Not every flat-faced dog has BOAS, and some never have breathing problems, but the risk rises the flatter the face.
In India this matters most through the summer and the monsoon. Heat and humidity both make the signs worse, and a dog that cannot breathe freely cannot pant effectively to cool itself, which is why flat-faced breeds are at higher risk of heatstroke.
When is a flat-faced dog's breathing an emergency?
If Loud, laboured breathing with the head stretched out, refusing to lie down.
Stop all activity, move the dog to a cool, air-conditioned room and call a vet straight away.
If Fainting or collapse, or gums or tongue turning grey or blue.
Go to the nearest 24-hour vet now. Keep the dog cool and calm on the way. Fainting is one of the life-threatening events BOAS can cause. PLOS ONE (2017)study
If Heavy panting, drooling, hot skin or vomiting on a hot day.
Treat as heatstroke: start cooling at once with cool water and moving air, then go to a vet. Merck Veterinary Manual
How do you care for a dog with BOAS?
Ask your vet to grade your dog's breathing, and discuss surgery early. Day to day, the aim is to keep the airway's workload low.
- Use a harness that does not pull on the neck, never a collar and lead. VCA Animal Hospitals
- Keep the dog lean: obesity raises BOAS risk and worsens the signs. PLOS ONE (2017)study
- Walk only in the coolest hours, keep exercise gentle, and avoid heat and humidity; use air-conditioning in summer. VCA Animal Hospitals
- Keep stress and over-excitement low, especially with visitors, fireworks and travel. VCA Animal Hospitals
- Ask about surgery to widen the nostrils, shorten the soft palate and remove everted saccules; it works best before two years of age. VCA Animal Hospitals
- Do not breed from dogs with marked breathing difficulty. VCA Animal Hospitals
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Questions owners ask
Is it normal for a Pug to snore?
- It is common, but it is not healthy. Snoring and snorting are the mildest signs of BOAS, a narrowed airway caused by the flat face. Many flat-faced dogs that snore also tire easily and overheat. Ask your vet to assess your dog's breathing, especially before an Indian summer.
Can BOAS be cured with surgery?
- Surgery cannot change the skull, but it can widen the nostrils, shorten the overlong soft palate and remove tissue blocking the larynx, which often improves breathing a great deal. Dogs operated on before two years old do better. Keeping the dog lean and cool still matters afterwards.
Why do flat-faced dogs overheat so easily?
- Dogs cool themselves mainly by panting, and a blocked airway makes panting hard work and less effective. Flat-faced dogs had about twice the odds of heat-related illness in a large UK study. Heat and humidity also make BOAS signs worse, so Indian summers and monsoons are risky.
Which breeds get BOAS?
- Mainly flat-faced breeds: the French Bulldog, Bulldog, Pug, Pekingese, Shih Tzu, Japanese Chin, Boxer and Boston Terrier. The flatter the face and the thicker the neck, the higher the risk, and obesity increases it further. Not every dog of these breeds is affected.
Keep reading
Related terms
More in health conditions
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- Bloat (GDV)Bloat, or gastric dilatation-volvulus (GDV), is when a dog's stomach fills with gas and twists on itself, cutting off its blood supply. It mainly affects large and giant deep-chested breeds. Unproductive retching, a swelling belly, drooling and restlessness are the signs. It is a surgical emergency that can kill within hours.
- Canine distemperCanine distemper is a serious viral disease of dogs that can attack the skin, airways, gut and nervous system. It spreads in droplets from coughing, sneezing and barking, and through body fluids. There is no specific cure, and some dogs do not survive even with treatment. The D in the DHPPi vaccine prevents it.
- Canine parvovirusCanine parvovirus, or parvo, is a highly contagious virus that attacks a dog's gut and immune system. It spreads through infected faeces, survives a long time in the environment and hits unvaccinated puppies between 6 weeks and 6 months hardest. Vomiting and bloody diarrhoea can kill within days, and it is prevented by the core vaccine.
- Cat fluCat flu is the everyday name for an upper respiratory infection in cats. More than 90% of cases are caused by feline herpesvirus, feline calicivirus or both. Cats sneeze, have runny eyes and nose and may stop eating. Most recovered cats remain carriers, and stress can bring the virus back. Vaccination usually prevents severe disease.
- Cherry eyeCherry eye is when the tear gland inside a dog's third eyelid slips out of place and shows as a smooth, red, cherry-like lump in the inner corner of the eye. It is common in young Bulldogs, Beagles, Shih Tzus and Pugs, and needs a vet, usually for surgery to put the gland back.
- Chronic kidney diseaseChronic kidney disease (CKD) is a slow, lasting loss of kidney function, common in older cats and also seen in older dogs. Early on there are often no signs; later a pet drinks and urinates more, eats less and loses weight. It cannot be cured, but a kidney diet, water and regular checks can slow it.
- DehydrationDehydration means a pet's body has lost more water than it has taken in, through heat, panting, vomiting, diarrhoea or illness. Early on the gums turn sticky; then the skin loses its spring and the eyes sink. A mildly dehydrated pet needs water and a watchful eye; a weak, vomiting or collapsing one needs a vet now.
- Dental diseaseDental disease in pets is mostly periodontal disease: plaque bacteria inflame the gums (gingivitis) and then destroy the tissue and bone holding the teeth (periodontitis). It is the most common disorder vets diagnose in dogs, and very common in cats. Bad breath, tartar and red gums are the early signs. Daily brushing prevents most of it.
- Diabetes in petsDiabetes mellitus is a lifelong condition in which a dog or cat cannot make or use enough insulin, so sugar builds up in the blood. Signs are drinking and peeing more, hunger and weight loss. Most diabetic pets live well on insulin injections given at set times with meals, and some cats go into remission.
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Sources
Each source was opened and read on the date shown. How Petym checks its sources
- University of Cambridge Department of Veterinary Medicine: About BOAS (Cambridge BOAS research group) (opens in a new tab)
- VCA Animal Hospitals: Brachycephalic airway syndrome in dogs (updated 30 July 2025) (opens in a new tab)
- Merck Veterinary Manual: What to do in a dog or cat emergency (opens in a new tab)
- PLOS ONE (2015): Impact of facial conformation on canine health: brachycephalic obstructive airway syndrome, Packer and others (opens in a new tab)
- Scientific Reports (2020): Incidence and risk factors for heat-related illness in UK dogs (opens in a new tab)
- PLOS ONE (2017): Conformational risk factors of BOAS in pugs, French bulldogs and bulldogs, Liu and others (opens in a new tab)