Brachycephalic (snub-nosed)
Short-muzzled breeds like bulldogs, pugs or boxers, with higher breathing risk under heat and stress. Many airlines restrict or refuse them in the hold, sometimes by season: check the breed list before planning.
Many airlines simply do not accept snub-nosed breeds in the hold, and several embargo them partially or by season, so the same dog may fly in spring and not in high summer. The reason they give is breathing risk under heat and stress. Of the three Spanish airlines we track, the only one publishing hold conditions excludes them outright. Check your airline's own breed list before planning anything, because the lists are not identical.