Run the same breathing exam, at the same registry, on three flat-faced breeds. You get 7.7% affected out of 117 Boston Terriers, 27.2% out of 232 Bulldogs and 29.9% out of 425 French Bulldogs.
That gap is what this page is about. It is not a claim that the breed is fine, and you will have three reasons to hold it loosely by the end. But it is real, measured the same way in all three, and almost nothing written about flat faces makes room for it.
The breed sits 23rd in the United States and has held that place since 2023.
Three weight classes, and no height
Most standards give a range; this one gives brackets. The American standard sorts the breed into three, and a dog is shown in its class: “Under 15 pounds; 15 pounds and under 20 pounds; 20 pounds and not to exceed 25 pounds.” Twenty-five pounds is the ceiling, and there is no floor.
Height gets no mention anywhere in the document, so the band in the panel above is our dataset’s rather than the standard’s, and the split between the sexes is our estimate rather than a measured one.
The head is where the standard commits itself. The muzzle is “short, square, wide and deep”, and “not exceeding in length approximately one-third of the length of the skull”. Hold that fraction: the measured version of it turns out to be the most surprising thing on this page.
The tail clause is unusually loose for a flat-faced breed: “straight or screw”, with both allowed.
How long they live, and why we cannot tell you
We would normally give you two or three measured lifespans here. For this breed we can give you none, and the reason is worth more than a guess.
The UK primary-care datasets that anchor most of our health writing barely contain this dog. In 2022, 1,603 Boston Terriers were registered with the UK Kennel Club, against 11,667 Bulldogs and 42,538 French Bulldogs. So when British researchers built life tables for eighteen breeds from 30,563 dogs, this one did not make the cut.
The largest UK longevity study, 584,734 dogs and 155 purebreds, may well hold a row for the breed. If it does, that row sits in a supplementary table we could not open, and we will not print a number we have not read.
What that paper does give is the skull-shape comparison. Flat-faced breeds reached a median of 11.2 years across 88,103 dogs. Medium-muzzled breeds reached 12.8 years across 267,753, and long-muzzled breeds 12.1 across 66,369. Dogs of all kinds sat at 12.5. That is the class this dog belongs to, which is not the same as a figure for the dog.
What is actually known about the character
Every breed sentence has a ceiling on it. A study of 18,385 dogs, 2,155 of them genotyped, concluded that “Breed explains just 9% of behavioral variation in individuals.” Nine parts in a hundred. The rest is the puppy, the household and the years.
Then the specific gap. The paper everybody cites for breed-level aggression is a C-BARQ comparison (an owner questionnaire with validated scoring), and it needed at least 45 dogs before a breed could appear. It ran two separate recruitments: 11 breeds through clubs and 33 through the open web. We read both tables, name by name. The Boston Terrier is in neither.
So when a page ranks this breed for biting, snapping or guarding, it is not reading that study, because that study has no row to read. We searched for a replacement and came back empty. Where the familiar character claims do come from is the breed standard, a club describing what it aims at. That is a target, not a measurement, and the two get confused constantly.
The first year and a half
Adolescence has been measured, and the study is stranger than the headlines suggest. It carries two different groups of young guide dogs. The first, 285 dogs, was scored for trainability by carers at 5, 8 and 12 months; 8 months was the trough. A separate group of 93 dogs was asked to sit on command at 5 and 8 months only. That is where the odd finding lives: they ignored the person who raised them while still obliging a stranger.
Owner complaints track the same shape. A British puppy cohort peaked at the 12-month survey: 513 owners of 1,219, or 42.1%, reported at least one unwanted behaviour, dropping to 29.9% by 18 months. Neither study enrolled this breed.
Three dates belong in this breed’s first eighteen months, and none are behavioural.
| Age | What is due |
|---|---|
| 9–15 months | when early-onset cataract, if present, becomes visible |
| 12 months | earliest age a breathing grade can be given |
| once, any age | BAER hearing test, if the breeder has not done it |
The middle row is the scheme’s rule. Grading starts at 12 months and the check is meant to be repeated every two years for a breeding dog.
The breed finishes growing early and is far too small for any of our large-breed growth warnings to apply. Keeping it lean is not cosmetic, though: see below.
Across their life
Nothing here is a diagnosis, and most Boston Terriers will meet almost none of it. Take it as a list of things worth raising while the dog is well.
One structural warning first. Because this breed is scarce in UK vet records, most of what follows leans on volunteered North American screening registries rather than on population data. When researchers followed 93 X-rayed dogs through the decision to submit or not, only 49 films were ever sent, and clean ones went in 8.2 times as often as bad ones. Every percentage below is therefore flattering, and each should be read as a lower bound.
The breathing figures, put side by side
BOAS stands for brachycephalic obstructive airway syndrome, soft tissue crowding an airway built shorter than its contents.
Two organisations grade it, both using the exam Cambridge developed. Here is what each has recorded.
| Source | Boston Terrier | Bulldog | French Bulldog |
|---|---|---|---|
| OFA register, % graded affected | 7.7% of 117 | 27.2% of 232 | 29.9% of 425 |
| Cambridge exercise test, % grade 0 | 37.5% of 104 | 15.2% | 10% |
| Cambridge exercise test, % clinically affected | 26.9% of 104 | 51.2% of 201 | 58.9% of 214 |
Read across the top row and the breed looks to be in a different league; read down the column and the reassurance thins out fast.
The registry row comes from the OFA’s breed statistics, and it is 117 dogs, few enough that a couple of dozen more submissions could move it several points, and all of them dogs an owner already believed would pass.
The test rows come from a Cambridge team who recruited 107 Boston Terriers and fully assessed 104 between 2021 and 2023. Grade 0 took 39 dogs (37.5%), grade I 37 (35.6%), grade II 27 (26.0%) and grade III one dog (0.96%). Grades II and III are the clinically affected end, and that is 28 dogs, 26.9% of the sample. Their own verdict is careful: “Boston Terriers appear to be less severely affected by BOAS than the most popular extreme brachycephalic screw-tailed breeds.”
Less severely affected. Not unaffected. The comparison column comes from the same team’s earlier work on 604 dogs of the three heavier breeds, where 51.2% of 201 Bulldogs and 58.9% of 214 French Bulldogs were affected, with 189 Pugs worst at 64.6%.
The windpipe tells the same story more cleanly. Tracheal hypoplasia is a windpipe narrow along its whole length rather than pinched at one point. Of 240 Boston Terriers graded, 0.4% were abnormal and 2.1% equivocal. The Bulldog figures are 6.0% abnormal and 7.1% equivocal of 2,338. One caution on the ranking: only five breeds are listed for this test at all, because only flat-faced breeds submit for it.
It is not the muzzle, and that is the surprise
The obvious explanation is that this breed simply has more nose. The measurements say otherwise.
Craniofacial ratio is muzzle length divided by skull length: the smaller the number, the flatter the face. The Cambridge paper quotes the published average for this breed at 0.14, and states plainly that this is less than the French Bulldog at 0.19 and the Bulldog at 0.22. By the measure everyone reaches for, Boston Terriers are the flattest-faced of the three.
That ratio still matters within the breed, where shorter-muzzled dogs were likelier to be affected. It fits the study that established the relationship across 700 dogs and a second group of 154, whose finding was blunt: BOAS “only occurred in dogs whose muzzles comprised less than half their cranial lengths.” Every dog in this breed is far inside that line.
So what is different? The neck, and the bulk behind it. Neck girth ratio divides neck circumference by chest circumference, and Boston Terriers came in at 0.62 for clear dogs and 0.63 for affected ones. The equivalent pairs are 0.66 and 0.70 in Bulldogs, 0.67 and 0.70 in French Bulldogs, and 0.67 in Pugs whether affected or not. This is a similar face on a much lighter frame: median body condition 5 out of 9, mean weight 7.8 kg across a range of 4.2 to 15.8.
Inside the breed, the strongest single risk marker was narrowed nostrils: odds ratio 2.51 (95% CI 1.18–5.85, p = 0.02). Body condition score did not reach significance here (p = 0.15), unlike in the heavier breeds, but that sample was lean to start with, so it is no argument for letting a Boston Terrier get fat. Our guide to judging a dog’s weight by hand is the practical end of it.
Two limits on all of it. Owners volunteered, mostly at shows and breeder health days, and the authors say straight out that “It remains difficult to determine the true prevalence of BOAS from an unbiased sample population within a breed.” And a broader survey of 898 dogs across fourteen flat-faced breeds, including 107 Boston Terriers, found shape explaining only about a fifth of who was affected.
That second study also graded the breed, and it is not a clean bill. It sorted breeds by the share scoring a clean zero, and put this one in the middle band: “A number of other breeds were defined as a moderate risk of BOAS with between 25–50% of dogs being Grade 0; the Griffon Bruxellois, Boston Terrier, Dogue de Bordeaux, King Charles Spaniel and Shih Tzu.” Middle, next to the Shih Tzu, not in the cleanest band with the Pomeranian and the Chihuahua.
The grade you can now ask for, and a page that argues with itself
Official certification opened to this breed in April 2026, when the OFA announced that thirteen more breeds “have been added to the list of breeds eligible for exams and official RFGS certification”, the Boston Terrier among them. The registry file already held 117 graded Boston Terriers by then, so some of that grading predates certification: OFA ran the exam on more breeds than it issued certificates for. Scroll further down the same page and you find a sentence that has not been retired: “The screening program is currently open to Pugs, Bulldogs, and French Bulldogs.”
Both are live at the same moment. The April update is newer, so we treat it as the current position, and we flag the older line because you will find it and wonder which to believe. The scale itself runs 0 to III: at the clean end a dog “is clinically unaffected and free of any respiratory signs of BOAS”, and at the other it “is clinically affected and has severe respiratory signs of BOAS.”
Eyes: the breed’s biggest measured problem
Here the news runs the other way. Of 10,425 eye examinations held by the OFA for this breed, 8.4% were abnormal, the largest sample and the largest finding in the breed’s whole registry file. It ranks 35th among the breeds listed for that exam. We could not confirm how long that list is, so for scale: the Pomeranian sits 216th on it, at 1.8% of 2,826.
Cataract is the part with the most work behind it, and there are two of them. They look similar and they are not the same disease.
Early-onset, or juvenile, cataract arrives in puppyhood. A 2007 DNA study compared 22 affected Boston Terriers with 40 that were clear or had the later form. It pinned the early disease on a single recessive variant in a gene called HSF4, and concluded that “the 2 forms of cataract in this breed are therefore genetically discrete conditions.” A cheek-swab test has existed ever since. Cloudiness and sight loss usually show between 9 and 15 months.
Late-onset cataract typically appears at three to six years. No genetic test exists for it. Two DNA-clear parents do not protect a puppy against it, and that is the most misunderstood point in this section.
For how common cataract is in total, the best figure available is North American: 1,693 of 15,241 Boston Terriers, 11.11%, in a specialist ophthalmology database. Those are dogs taken to an eye specialist, so it is not the breed’s true rate.
The DNA test itself now has registry numbers: 804 dogs tested, 97.0% clear and 3.0% carriers, second among the breeds submitting for it. A carrier is healthy. Two carriers bred together are how affected puppies happen.
A note on the ulcers you will read about elsewhere. The eyes sit in shallow sockets, and every breed guide warns about scratched corneas. We could not find a measured rate for this breed. An English study of 104,233 dogs found corneal ulceration in 834 of them, 0.80% overall, and put the Pug highest at an odds ratio of 19.05, then the Boxer at 12.12 and the Shih Tzu at 10.04. This breed is in none of its tables, which is evidence it is rare in Britain, not evidence it is safe.
Birth: the number where this breed is worst of all
If you are considering breeding, read this before anything else on the page. A survey covering 22,005 litters from 13,141 bitches across 151 breeds counted 48 of 52 Boston Terrier litters delivered by caesarean section, 92.3%. Only two other breeds passed 80%: the Bulldog at 248 of 288 (86.1%) and the French Bulldog at 65 of 80 (81.3%).
This breed is top of that list. Fifty-two litters is a small count and the reporting came from breed club members, who are not a random sample of breeders, but no amount of sampling bias turns 92.3% into a normal delivery rate. Surgery is the route, and it should be budgeted for rather than hoped against.
Hearing, and what the white markings do and do not mean
The standard requires white: a “white muzzle band, white blaze between the eyes, white forechest”, with a solid black, brindle or seal dog disqualified from the ring for lacking them.
People reasonably ask whether that white brings deafness with it, as it does in some breeds, and the honest answer is that nobody has shown it here. The standard reference on inherited deafness lists this breed among those with “high prevalence rates” but attaches no figure to it. The piebald link itself has been demonstrated in a specific set of breeds: Dalmatian, English setter, English cocker spaniel, border collie, Australian cattle dog and Jack Russell terrier. This one is not among them.
What we do have is a count. Of 4,318 BAER hearing tests recorded for the breed, 1.2% were abnormal, ranking it 17th among the breeds that submit. BAER measures the brainstem’s electrical answer to a sound, and it is the only way to catch a puppy deaf in one ear, which behaves normally at home. Ask whether it was done.
The tail gene, and where this breed parts company
The screw tail is a variant in a gene called DVL2, which helps lay out the skeleton in the embryo. Researchers who genotyped 177 dogs from screw-tail breeds included 65 Boston Terriers. Every dog carried two copies except six of them: four with one copy, two with none.
That detail is the whole point. The variant “was fixed in Bulldogs and French Bulldogs”, meaning no unaffected line exists there to breed toward. Here it runs at an allele frequency of 0.94: high, but not total. It fits a standard that permits a straight tail as readily as a screw one.
The same variant tracks with malformed vertebrae, and the imaging numbers are far too thin to lean on. That paper never says how many Boston Terriers were scanned; it gives only a penetrance of “45–100%” for chest malformations across its three breeds together. A 2024 review of the published scans turns up one relevant study. Of 175 neurologically normal dogs checked for narrowing of the spinal canal in the chest, 18.8% were affected: 39% of 41 English Bulldogs, 28.3% of 60 French Bulldogs, 0% of 68 Pugs and 0% of the six Boston Terriers. Six dogs is a hint, not a result, and that pug row, on 68 dogs, is the better reminder that this one is not really about screw tails.
Either way, a malformed vertebra on a scan is not a disease. Weakness, wobbling or pain in a young dog is a same-week appointment whatever its tail looks like.
Joints, teeth, and the rest of the file
A placing is only worth as much as the number of breeds ranked, and OFA lists only breeds whose owners actually submit. Where we could not confirm how long a list is, the table says so.
| Test | Evaluated | Abnormal | Placing |
|---|---|---|---|
| Eyes | 10,425 | 8.4% | 35th; list length unconfirmed |
| Dentition | 92 | 15.2% | 13th; list length unconfirmed |
| Hips | 598 | 12.5% | 103rd of 219 |
| Patellas | 5,405 | 4.9% | 38th; list length unconfirmed |
| Hearing (BAER) | 4,318 | 1.2% | 17th; list length unconfirmed |
| Windpipe | 240 | 0.4% (+2.1% equivocal) | 4th of 5 |
| Breathing grade | 117 | 7.7% | 4th, behind the Pug, Bulldog and French Bulldog |
| Cataract DNA | 804 | 3.0% carriers | 2nd of the few breeds that submit |
Read the breathing row the right way up: the three breeds placed above it all scored worse, so 4th here is the good end.
Three rows need a sentence each.
Dentition at 15.2% is on 92 dogs. Ninety-two. Crowded, rotated or missing teeth follow a shortened jaw, so the finding is believable, but a figure built on that few evaluations is not the breed’s rate, and we will not quote it as one.
Hips at 12.5% of 598 put the breed 103rd of the 219 breeds ranked: the middle of the field, and a long way from the Bulldog’s 70.8%. Dysplasia is graded from a radiograph, and a dog can score badly on film yet walk normally for life.
Patellas at 4.9% of 5,405 is the biggest joint sample the breed has. The largest English study of kneecap dislocation covered 210,824 dogs and found it in 1.30% (95% CI 1.21–1.39), the Pomeranian highest at an odds ratio of 6.5. This breed is missing from that paper’s tables too.
What to ask a breeder for
This is the shortest useful part of the page. The breed club asks its members for four things. Three are the American registry’s requirements. The fourth the club adds itself:
- an eye exam by a board-certified ophthalmologist, annually
- a patella examination, every two years
- a BAER hearing test, once in the dog’s lifetime
- the DNA test for early-onset juvenile cataract, once in the dog’s lifetime
Since April 2026 you can ask for a fifth: a dated breathing grade on both parents. Every one of these is a document rather than a photograph or a promise.
What we could not verify
A lifespan for this breed. The largest UK study holds one in a supplementary table we could not open, and no life table covers the breed. We would rather leave the row blank than fill it from a content farm.
Any temperament ranking. The breed is absent from both recruitment arms of the standard cross-breed survey. We read both breed tables in full.
A daily exercise figure. Nothing measures it. For a dog where exertion is what exposes a marginal airway, a fixed minute count would be worse than none.
That the muzzle explains the better breathing. We went looking for that mechanism and the measurements refused it. Neck girth and overall build are the candidates left standing, and nobody has tested either directly.
Whether the breathing advantage will last. Certification only opened to the breed in 2026, and 117 graded dogs are too few and too recent to read a trend from.
What the 7.7% would look like at scale. One hundred and seventeen dogs is the thinnest evidence carrying the most weight on this page. It points the same way as a separate 104-dog exercise-tested sample, which helps, and neither is large. If you take one caveat away, take that one.