Why flat faces are the problem
Brachycephalic animals have a shortened skull but a normal volume of soft tissue, which narrows the airway. Many have some degree of brachycephalic obstructive airway syndrome — stenotic nostrils, an elongated soft palate, a narrow windpipe. Dogs cool themselves mainly by panting, and panting through a restricted airway is both less effective and more tiring. Add the heat, noise and stress of a hold flight and a dog that copes fine at home can decompensate quickly. The restrictions exist because carriers have recorded a disproportionate share of in-transit deaths in these breeds.
Which animals count
The usual dog list includes English and French bulldogs, pugs, boxers, Boston terriers, shih tzus, Pekingese, Lhasa apsos, Cavalier King Charles spaniels, bull mastiffs and Japanese chins. On the cat side it typically covers Persians, Himalayans, Exotic Shorthairs and Burmese. Every airline publishes its own list and they do not match, so a breed banned by one carrier may be accepted by another. Crossbreeds are frequently included where the flat-faced parentage is visible, and staff at check-in can make that call on the day.
What carriers do in practice
Responses fall into three groups. A number of airlines refuse snub-nosed breeds in the hold outright, all year and on every route. Others allow them only outside a seasonal embargo or below a ground-temperature threshold at departure, transit and arrival airports. A third group accepts them in the cabin, where the animal stays in a temperature-controlled space with you, but not as checked baggage or cargo. Policies change, so get the current rule in writing from the airline for your specific route rather than relying on a forum post or a booking agent.
Reducing risk when you do fly
If a carrier accepts your dog, most will require a crate one size larger than the measurements alone suggest, with extra ventilation. Book direct flights to avoid a second loading cycle, and choose departure times when the ground temperature is lowest — early morning or overnight in warm months. Skip sedation: veterinary guidance is consistent that sedatives depress breathing and interfere with temperature regulation, which is exactly the wrong combination here. A pre-flight examination focused on airway function tells you whether the animal is a reasonable candidate at all.
Routes that avoid the hold
Where the answer is no, the realistic alternatives are ground and sea. Road transport works well within a continent, including specialist pet ground-transport operators who drive climate-controlled vans over long distances. Some ferry and cruise routes carry pets in cabins or in kennels, which suits crossings such as the English Channel or transatlantic sailings. Relocation companies can also route via a country where the airline’s policy differs. If none of these fits, delaying the move until a cooler season is a legitimate option rather than a failure.