A study looking at the health impacts selective breeding has had on French Bulldogs has shown they have a higher risk of developing 20 common disorders than other dog breeds.

Researchers found they are 42 times more likely to suffer from narrow nostrils and 30 times more likely to develop obstructive airways syndrome, compared with other breeds.

The research, published in Canine Medicine and Genetics, was carried out by the Royal Veterinary College, U.K. It looked at health data on 2,781 French Bulldogs and 21,850 dogs of different breeds.

French Bulldogs are a small and stocky breed of dog, with broad, square-shaped heads. They are characterized by their short noses and wrinkled skin around their face and shoulders. A previous preference for these features by kennel clubs and owners has led to French Bulldogs being selectively bred to the point where they suffer many health problems.

They are known to have spine malformations, breathing issues and skin problems. Generally, they are not able to reproduce naturally, requiring artificial insemination and often cesarean section to give birth.

Their popularity is huge, however. In March it was announced that French Bulldogs are now the second most popular dog breed in the U.S.

In the latest study, Dan O'Neill and colleagues looked at 43 health conditions on a veterinary database, comparing the proportion of French Bulldogs diagnosed with those of other breeds.

Their findings showed that French Bulldogs were slightly less likely to be diagnosed with health conditions overall. However, they were significantly more likely to develop 20 of the 43 conditions studied. These include narrowed nostrils, obstructive airways syndrome, ear discharge and skin dermatitis.

Stock image of a French Bulldog. Scientists in the U.K. have found the breed is more likely to develop 20 health conditions compared with other types of dog. Getty Images

"These results identified ultra-predispositions with worryingly higher odds in French Bulldogs for several disorders, suggesting that the health of French Bulldogs has diverged substantially from, and may be lower than, the health of the wider non-French Bulldog population," the team wrote.

"Many of these predispositions are closely associated with the conformational extremes that define the French Bulldog breed. Shifting the typical conformation of the French Bulldog population towards a more moderate phenotype is proposed as a logical opportunity to reduce the serious health issues endemic in the French Bulldog breed."

The researchers also found French Bulldogs were likely to suffer from obesity, lameness and undesirable behaviors. This, the authors say, means breeding towards a healthier appearance could improve the health profile of French Bulldogs overall.

The Kennel Club in the U.K. recently changed its breed standard to favor dogs with longer noses, and away from those with flatter faces. One breeder in the Netherlands is currently working to "reengineer" the French Bulldogs face by selecting those with longer muzzles in order to improve the health of the breed overall.

"Achieving meaningful changes to the typical look of French Bulldogs over time requires buy in from breeders and kennel clubs who publish breeding standards, but the biggest responsibility lies with owners who ultimately can demand dogs with more moderate features," O'Neill said in a statement.

"The Kennel Club have recently updated the breed standard for the French Bulldog to move further away from elements of extreme conformation with evidence of health ill-effects. This is a very positive step to prioritize the health of dogs over human desires for how these dogs look and we must now continue this evolution of the breed towards a more moderate conformation."