Brachycephalic obstructive airway syndrome (BOAS)

What it is

Brachycephalic obstructive airway syndrome (BOAS) is a breathing disorder of dogs with short skulls and flat faces. Breeding has shortened the skull, but the soft tissue inside the nose and throat has not shrunk to match. The result is a crowded nasal cavity and partial blockage of the throat (pharynx) and voice box (larynx)^[1].

Because air has to be pulled through a narrow airway, the dog has to work harder to breathe in. That effort sucks soft tissue further into the airway, the tissue thickens over time, and the cartilage of the larynx can collapse, which makes the blockage worse^[1]. The University of Cambridge describes BOAS as a progressive disorder that can impair a dog’s ability to exercise, play, eat and sleep^[4].

Several parts of the airway can be involved: narrowed nostrils, an over-long or thickened soft palate, overgrown nasal turbinates, enlarged tonsils, everted laryngeal saccules and laryngeal collapse^[2][3]. Excess weight makes it worse, because fat narrows the airway further. Obesity (a body condition score of 7 or more out of 9) is significantly associated with BOAS^[3].

Signs to look out for

Many owners see snoring and snorting as part of a flat-faced breed’s character. The BVA reports that vets find most owners of these breeds do not recognise breed-related health problems^[8]. Signs to watch for include^[2]:

• Noisy breathing. Snoring-type noise usually comes from the soft palate, and some dogs snore while awake. A high-pitched noise suggests a problem at the larynx. Some dogs are only noisy when excited, exercising, eating or stressed.
• Narrow nostrils, sometimes with the dog switching to mouth breathing after gentle exercise.
• Struggling with exercise, such as tiring quickly or open-mouth breathing.
• Struggling in heat. Affected dogs cannot cool themselves well and are at risk of heatstroke. Heavy panting, drooling and a racing heart are warning signs.
• Disturbed sleep, including pauses in breathing.
• Regurgitation or trouble eating, linked to swallowing problems and reflux.
• Blue tongue or gums, or collapse. These mean the dog is not getting enough oxygen and need emergency treatment.

How it’s diagnosed and treated

A vet will examine the dog and listen to its breathing at rest and after exercise. The Cambridge grading system uses a three-minute trotting test and grades dogs from 0 to III, with grades II and III counted as clinically affected^[2]. Some referral centres also use a non-invasive breathing chamber test, X-rays and CT scans, and an examination of the throat and nose under sedation or general anaesthetic to plan surgery^[2].

For breeding dogs, the Kennel Club and University of Cambridge run a Respiratory Function Grading scheme for French Bulldogs, Pugs and Bulldogs. Grade 0 means no breathing signs of BOAS, and the scheme advises that grade 3 dogs should not be bred from^[4].

Treatment starts with management: weight loss for overweight dogs, and avoiding heat and stressful situations^[3]. Weight loss may be suggested before surgery for obese dogs with mild to moderate signs^[3].

Surgery aims to open the airway. Depending on the dog, it can include widening the nostrils, shortening or thinning the soft palate, partly removing enlarged tonsils and removing everted laryngeal saccules. Some Pugs and French Bulldogs with severe nasal blockage are offered laser surgery to remove overgrown turbinates^[3]. The main risk is during recovery from anaesthetic, when swelling can block the airway, and there is also a risk of aspiration pneumonia from regurgitation^[3]. BOAS cannot be cured, but surgery can improve quality of life, and severe cases may need further surgery later^[3].

Published UK prices range from about £1,000 for a fixed-price package at one general practice group to £3,200 or more at referral hospitals, before consultations, imaging or complications (see the cost table).

Breeds most affected

French Bulldogs, Pugs and Bulldogs are the breeds most strongly linked with BOAS. In UK vet records from 2016, French Bulldogs had about 31 times the odds of a BOAS diagnosis compared with other dogs^[6].

A 2026 Cambridge study assessed almost 900 dogs from 14 other breeds. Pekingese (89% affected) and Japanese Chin (82%) had rates the researchers described as comparable to Pugs, French Bulldogs and Bulldogs. King Charles Spaniels, Shih Tzus, Griffon Bruxellois, Boston Terriers and Dogues de Bordeaux were at moderate risk. Staffordshire Bull Terriers, Cavalier King Charles Spaniels, Chihuahuas, Boxers and Affenpinschers were at mild risk, and no Pomeranians or Maltese were clinically affected^[5].

Flat-faced cats are also reported with BOAS. Persian cats can have narrow nostrils, compressed nasal bones and occasionally an over-long soft palate, although unlike dogs they are not reported to have a narrowed windpipe. A large UK study of Persians under vet care did not find clear evidence of extra breathing disorders compared with other pedigree cats, so the size of the problem in cats is less certain^[7].

How insurers treat it

Most policies exclude conditions that existed before cover started and illness that starts in the first 10 to 14 days^[13]. With BOAS, the dispute is often about when the condition “started”. In one ombudsman case, an insurer declined a claim for BOAS surgery because a vet had noted narrow nostrils three days into cover. The ombudsman decided the note described normal anatomy for the breed rather than a sign of illness and told the insurer to reconsider the claim, adding that an insurer wanting to exclude this kind of surgery should say so clearly in its terms^[14]. In another case, the insurer’s underwriting rules would have excluded the whole respiratory system because the dog coughed during the waiting period. The ombudsman again found for the owner, because the coughing had not been shown to be linked to BOAS^[15].

Some policies exclude hereditary and congenital conditions outright, and accident-only policies do not cover BOAS^[16]. If you have a flat-faced breed, read the exclusions section of the policy wording for any mention of breathing, respiratory, hereditary or brachycephalic conditions before you buy. Also check whether the vet fee limit is per year or per condition, because time-limited and maximum benefit policies cap how long or how much they pay for a single condition^[13].