French bulldogs, with their marble-like eyes and pleated faces, are beloved by celebrities and ordinary people alike.

Really, really beloved. In the United States, Frenchies didn't even rank in the American Kennel Club's top 30 most popular breeds in 2007. Last year, they were No. 4. In Britain, they ranked 76th in 2005. Now they're in second place and on track to snag the top spot from the Labrador retriever by the end of this year, according to that nation's Kennel Club.

But French bulldogs, as dogs go, are also quite unhealthy.

They're one of the brachycephalic breeds — dogs whose human-selected large heads and flat faces make them prone to certain ailments. The difficulty these breeds have breathing through their smushed noses is so severe that several airlines refuse to fly them in cargo. 

United joined those carriers this week, two months after a French bulldog suffocated in the overhead compartment of one of its planes, where the animal had been placed by a flight attendant.

"These dogs are kind of a dream for people who want to do research on pathology, on disease, in dogs," said Dan O'Neill, a senior lecturer at the Royal Veterinary College in London. "Because they've got lots of problems."

That's bad for Frenchies, of course, but O'Neill says it has also become a crisis for what he calls "dogdom" — precisely because of their astronomical rise. That trend will mean more ailing animals at veterinary clinics, costlier bills for owners and more castoffs in shelters, not to mention a major incentive for unscrupulous breeders to churn out puppies with little concern for their health or welfare, he added.

"These dogs came out of nowhere in 10 years," said O'Neill, the lead author of a new study on the breed's demographics and disorders. "They are unhealthy, but it's their rising popularity that makes it a huge issue."

To get a better picture of this burgeoning pooch population's health in Britain, O'Neill and other researchers pulled records on all dogs treated at more than 300 clinics in 2013. They ended up with 2,228 French bulldogs and some revealing data points.

Of the puppies born that year and seen in those clinics, 1.46 percent were Frenchies — up from just 0.02 percent in 2003, which the authors call an "unprecedented" growth for a single breed. What's more, the French bulldogs' median age in 2013 was 1.3 years, compared to about 4.5 for all dogs. That indicates many were acquired quite recently.

Despite their youth, 72 percent had some sort of disorder. Some of the most prevalent were common canine issues such as diarrhea or ear infections. But several were "conformational" disorders, or maladies related to the physical appearance that fanciers have decided French bulldogs should have.

The ailments included skin fold dermatitis, a stinky and uncomfortable bacterial infection that develops between the dogs' wrinkles, and corneal ulcers, a painful condition that can result from eyes so bulging that they don't fully close when a dog blinks. Not surprisingly, five of the 25 most prevalent problems were upper respiratory disorders.

"That would not be the case with dogs overall," O'Neill said. And the Frenchies' youthfulness gave "a very rosy-eyed view" of their breed's health, he added. "When these dogs reach middle age, these values are going to rise dramatically."

Doing this kind of analysis would be challenging in the United States, where there's no central source that collects clinical data from veterinary practices. (O'Neill designed the one used in Britain, VetCompass, and said he's unsuccessfully pitched it in the United States.) But there's every reason to believe that American French bulldogs' results would be similar, O'Neill said, because the conformation standard for the breed is pretty much the same.

The health woes of brachycephalic dogs have gotten far more attention in Britain, where a critical BBC documentary on purebreds set off a national conversation a decade ago. Today, O'Neill chairs the Brachycephalic Working Group, a body of veterinarians, breed clubs, scientists and animal charities focused on trying to improve flat-faced dogs' welfare as well as reduce demand for them. The new study provides the group with valuable data on French bulldogs' problems, he said.

"We're certainly not pillorying owners because they have chosen this breed. If they've already got the breed, we want to help them," O'Neill said. But, he added, "Perhaps the next time, don't get this breed. There are other beautiful dogs out there."

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