Brachycephalic obstructive airway syndrome
The breathing disorder that comes with a flat face — narrowed nostrils, an overlong soft palate and a cramped throat that together make ordinary air hard to move.
A shorter muzzle does not come with a shorter set of soft tissue. The nose, palate and throat of a flat-faced dog are folded into a skull bred progressively shorter, so the airway is pinched at several points at once. Owners often hear the snoring and the snorting as breed character rather than as a dog working hard to breathe.
Severity runs from mild to life-threatening, and vets can measure it: a graded walk test before and after exercise puts a number on how much the airway is costing the dog. Surgery to widen the nostrils and shorten the soft palate helps many. Heat makes all of it worse, because panting is how a dog sheds heat and BOAS is a limit on panting.