The most striking thing about Sidney’s mouth, which has been hoisted wide open with rope, is his teeth. They are in unusually good condition for a four-year-old bulldog. His incisors, while gappier than a row of gravestones, are a brilliant white and his tusk-like canines gleam like polished ivory under the surgical lights. Further down the dog’s jaw, however, the picture is less healthy. Sidney can’t breathe properly. He has been put under at Battersea Dogs & Cats Home for an operation that may help.

As Sidney waited in a holding pen at the animal home’s hospital, he and Frankie, a similarly affected French bulldog two doors down, could be heard snorting and gasping, even at rest. They suffer from brachycephalic obstructive airway syndrome (BOAS), which is estimated to affect half of all brachycephalic (flat-faced) dogs, most notably bulldogs, French bulldogs and pugs. Shaun Opperman, Battersea’s veteran head vet, has scrubbed up for an operation he now performs with alarming regularity.

What follows is gory, but Opperman is keen to reveal – in bloody detail – what happens when pet trends fuelled by social media combine with decades of unnatural selection to create a cycle of cruelty, unregulated trade, abandonment and early death. As breathless breeds become more popular and the animals age, vets warn the cycle is about to get much worse. “This is a calamity waiting to happen,” says Dan O’Neill, a BOAS expert and a veterinary epidemiologist at the Royal Veterinary College in Hertfordshire.

Q&A What sort of health problems do brachycephalic dogs have? Show Breeds such as pugs, bulldogs, French bulldogs and boxers are prone to a range of health problems, many of which are related to their short skulls and other characteristic features.

Breathing problems Brachycephalic breeds often have narrow nostrils, deformed windpipes and excess soft tissues inside their nose and throat – all of which can lead to difficulties with breathing, which can also lead to heart problems. The dogs are also prone to overheating.

Dental problems

The shortened upper jaws of squashed-faced dogs means their teeth are crowded, increasing the risk of tooth decay and gum disease.

Skin disorders The deep folds around the dogs’ faces, such as the characteristic wrinkles of a bulldog, also bring problems as they are prone to yeast and bacterial infections. Eye conditions The head shape and prominent eyes of brachycephalic breeds means the dogs are at risk of eye conditions including ulcers. Among the causes of eye ulcers is that brachycephalic dogs often cannot blink properly and have problems with tear production, while eyelashes or nasal folds can also rub the surface of their eyes.

Birth problems

Brachycephalic breeds can have difficulties giving birth naturally because of the disproportionate size of the puppies’ heads, meaning that caesarean sections are often necessary. According to recent research more than 80% of Boston terrier, bulldog and French bulldog puppies in the UK are born in this manner.

The problem for the big three “brachy” breeds is that they are too cute for their own good. Breeders have selected the animals with the biggest eyes and the funniest faces to meet demand among fickle owners. French bulldogs, known as Frenchies, have enjoyed – or endured – a startling spike in popularity, with their puppies selling for several thousand pounds. Their little faces, pointy ears and clownish personalities dominate dog Instagram, where more than 20m posts bear the #frenchbulldog hashtag. Celebrity owners have included Madonna, Lady Gaga and David Beckham.

The Kennel Club, which records puppy registrations, counted almost 37,000 French bulldogs in 2018, compared with only 1,007 10 years earlier. Pug and bulldog numbers, meanwhile, roughly doubled in the same decade, up to about 10,000 each last year. Beyond the Kennel Club’s books, the breeds’ true populations are likely to be several times higher.

But scrunched skulls and snouts leave little room for breathing. “The skeletal features have changed, but the soft tissues haven’t adapted with them,” Opperman explains, poking Sidney’s pink, fleshy soft palate, right at the back of the roof of his mouth. It is too big, occupying the space where air that arrives from the nose should flow freely into the windpipe and lungs. Opperman uses a long clamp with a tight curve at its end to grab a chunk of Sidney’s palate. He then reaches for a cauterising tool and runs it along the clamp, cutting away at the palate.

Shaun Opperman, Battersea’s head vet, and Emily Friend, a veterinary nurse, remove tissue from Sidney’s throat and nose. Such operations are becoming increasingly common, Opperman says. Photograph: Jill Mead/Guardian

The acrid smell of burnt flesh fills the room as smoke curls out of the dog’s mouth. Within a few minutes, Opperman has cut out a 3cm morsel of meat, which he drops on a surgical tray. He reaches for a curved needle and removes the clamp. Blood-soaked gauze stuffed down Sidney’s throat has to be replaced while Opperman stitches the cut.

“We tend to normalise this condition,” Opperman says. Last year, Battersea performed 62 BOAS surgeries, versus seven in 2015. This reflects growing numbers of the three affected breeds at the home, which took in 40 French bulldogs alone last year (up from eight four years earlier), abandoned by often naive owners. “We tend to say: ‘Oh, it’s a French bulldog – it’s normal for them to breathe like that,’” Opperman says. “But if your child sounded like that after a walk in the park, you’d have him straight down to A&E.”

“Eleven blade, please.” Emily Friend, a veterinary nurse, hands Opperman the correct scalpel for the next part of Sidney’s surgery. The team have lowered his jaw and now turn to his nose. It is also squashed, its little nostril flaps acting like closed doors. “You should be able to see inside,” Opperman says. “Imagine trying to breathe like that.”

Dogs sleep with closed mouths. But some animals with BOAS find ways to prop them open to survive the night, using furniture or toys as wedges. If not, they can wake up repeatedly with startled snorts. Extreme sleep deprivation is common, leading to even less exercise than their airways allow anyway. This can result in obesity, which only worsens the condition, making sleep harder. Vets report seeing dogs so tired that they nod off in consultations while still standing.

Some animals with BOAS find ways to prop their mouths open to survive the night, using furniture or toys as wedges

Before Sidney’s surgery, Frankie, the French bulldog, was in theatre. However, as Opperman tried to inject the anaesthetic into his shaved paw, he panicked, flinching and showing his teeth. He will come back another day. Opperman, who has worked at Battersea for 27 years, thinks stress may have brought forward the dog’s perpetual background fear of suffocation. “Pain is one thing,” he says. “But if you’re short of breath it inspires panic and dread. It’s an emotional discomfort.”

Scalpel in hand, Opperman reaches towards Sidney’s nose. He cuts out what he calls a “Trivial Pursuit wedge” from the middle of each nostril flap, preserving its edge but reducing its size in a way that leaves those doors ajar. Blood drips and pools on the floor as Opperman stitches the cuts as quickly as he can.

Despite the final indignity of castration, which ends his 40 minutes in theatre (neutering is a standard procedure for dogs in Battersea’s care), Sidney has escaped more extreme BOAS complications and procedures. Opperman will often cut out tonsils to clear more space. Further obstructions can exist behind the nostrils, which can sometimes be cleared with more invasive laser surgery.

BOAS dogs can suffer from oxygen starvation, leading to fainting and other problems. The constant fight to draw in air can also create a destructive negative pressure inside the animals. Over time, this weakens harder structures such as the larynx, causing them to narrow or even collapse, further obstructing the airway.

Reality TV star Pete Wicks has become an advocate for brachycephalic dogs since the unexpected death of his French bulldog, Ernie (not pictured). Photograph: Ken McKay/ITV/Rex/Shutterstock

If they don’t become obese, BOAS dogs can become starved of food as well as oxygen; the fleshy throat obstructions can make eating and swallowing difficult, causing frequent regurgitation. The buildup of pressure, meanwhile, can pull at the digestive tract, drawing out fleshy folds and even pulling up the stomach into the chest, causing reflux.

Surgery can prevent this decline, particularly while dogs are still young, but it isn’t always successful or even sensible. “If you’ve got a young, skinny dog with laryngeal collapse or worse, who is already really struggling, we do talk with owners about putting them to sleep,” says Jane Ladlow, a specialist surgeon at the Queen’s Veterinary School hospital at the University of Cambridge.

Euthanasia due to BOAS is thought to be rare; Battersea says it has taken the decision only twice. But Opperman expects the problem to get worse as more French bulldogs, in particular, arrive in his care. “It was 60 operations last year and I suspect we’ll get to 100 this year – and who knows after that,” he says. “We’re typically a couple of years behind the trends. What’s fashionable now becomes a vet bill in two years’ time.”

Pete Wicks remembers first spotting a French bulldog in Shoreditch, east London, more than five years ago. The star of The Only Way Is Essex and Celebs Go Dating had also followed the exploits of a French bulldog called Herby on Made in Chelsea.

“I was the same as everyone else – I liked the way they looked and thought: ‘That’s a cool dog,’ but didn’t know much about it,” Wicks says. In 2014, he bought a puppy from a breeder for £4,000. Ernie, a “proper geezer”, appeared with Wicks on TV and on his Instagram, where Wicks has more than 1 million followers. The dog had become one of the growing army of Frenchies that now fill our parks and social media feeds. “You go into a pub now in London and you’re going to see at least one Frenchie,” Opperman says.

Scientists have long studied the “baby schema” effect, by which humans are drawn to animals with infantile features, including big eyes, flat, round faces and a general podginess. But the power of the influencer may have as much to do with the Frenchie’s rise. Some of the influencers are dogs themselves; Manny the Frenchie, an eight-year-old based in Chicago, has 1.1 million Instagram followers, as well as a range of merchandise including tote bags and iPhone cases.

Insurance premiums for the dogs can be high ... an operation for BOAS can easily come to £3,000

In 2016, Ernie died due to a heart problem. Wicks doesn’t think it was related to his breathing. Distraught and moved to learn more about the breed, he was shocked to discover the level of suffering the dogs can endure. He now works with dog charities to expose some of the ways in which unscrupulous suppliers are meeting rising demand. But until new legislation kicks in that is due to ban the sale of puppies and kittens by anyone who has not bred them, buying a Frenchie is easy. At the time of writing, there are 430 adverts for Frenchies on the listings site Gumtree, ranging in price from £300 to £5,000. Many may be healthy and listed by good breeders, but there is nothing to stop deals taking place in pub car parks, no questions asked.

Puppy farms in Britain and eastern Europe are meeting demand. The worst among them are selecting for extreme features, worsening the deformities that cause BOAS, as well as conditions that affect eyes and skin. Dogs Trust, Britain’s largest dog welfare charity, quarantines and rehomes puppies seized at ports. Linda Goodman, the founder of Cariad, a campaign to end puppy farming, says social media are to blame for “crucifying” the breeds. “People are still so set on having them that it kind of bypasses them that they are buying into cruelty,” she says.

The Kennel Club, which recently launched a BOAS assessment and grading system in partnership with Ladlow at Cambridge, advises would-be owners still intent on getting a brachy dog to use registered breeders or rescue homes. No buyer should get a puppy from a private seller without first observing the dog’s home and parents and checking for breathing problems. Existing owners concerned about their dog’s breathing should see a vet.

‘We tend to normalise this condition,’ Opperman says. ‘But if your child sounded like that after a walk in the park, you’d have him straight down to A&E.’ Photograph: Jill Mead/Guardian

After Ernie’s death, Wicks vowed only to home rescue Frenchies. He now uses social media to raise awareness and promote the #adoptdontshop hashtag (24m posts and counting). He got Eric, now three, from Dogs Trust, after he was smuggled from Lithuania. He also has Peggy, an 18-month-old Frenchie who had to have an eye removed after it got ulcerated – another common problem in the breed. Wicks pays about £300 a month to insure the animals. Premiums for the dogs can be high; an operation for BOAS can easily come to £3,000.

Vets are still establishing the scale of the problem, but the Royal Veterinary College, the UK’s largest referral hospital, now has a dedicated BOAS unit with eight surgeons. They carried out about 200 airway operations last year. At Cambridge, Ladlow says her team performs up to four a week. “We could triple that if we wished,” she says.

The Kennel Club, which has been accused in the past of perpetuating unhealthy traits, says it is tackling the problem from the top, by challenging show breeders to select dogs with better airways. Ladlow says she has already started to notice quieter kennels at dog shows. Beyond the canine elite, the club is working with charities to raise awareness, increase diagnoses and challenge advertisers to stop glorifying affected breeds. It promotes healthier breeds such as the norfolk and norwich terriers. But, as Opperman points out, the healthiest dogs tend to be mongrels.

The best Sidney can hope for is an easier life. As his testicles and chunks of his throat and nose lie in the theatre ready for disposal, he shakes his head suddenly as he starts to come round. Opperman slides the breathing tube from his mouth. Air begins to flow through his widened nostrils. “All right, sweetheart, you’re all right,” the vet tells the dog. A few days later, kennel staff report that Sidney is recovering well and showing early signs of improvement. They will soon put him up for adoption.