Zoovet Veterinary Technical Series — Vol. III — Air transport of brachycephalic dogs
Global reference guide — Zoovet Travel Technical Series, Volume III
Zoovet Travel — Veterinary Clinical Unit and International Export Advisory, Peru
Correspondence: info@zoovettravel.com
Vol. III — 2025Over the last fifteen years, veterinary consultations related to the air transport of brachycephalic breeds have increased in parallel with the popularity of these breeds. According to O'Neill et al. (2018), the French Bulldog moved from a marginal breed in the United Kingdom to one of the most registered, with all that this implies for the international mobility demands of their owners.
The airline industry response has been gradual but sustained: progressive hold restrictions first; in some cases extension of limitations to the cabin thereafter. The declared rationale in every case is the same: the greater respiratory vulnerability of these breeds to the conditions of the aeronautical environment. That vulnerability has a genuine physiological basis, which is the central subject of this review.
The correct question is not "can brachycephalic dogs fly?" but "under what conditions, with what level of risk, and in which specific dog?" Answering that question with rigour requires first understanding why these animals represent a group with differential physiology in the context of air transport.
Pathophysiological basis — peer-reviewed published science
In clinical practice, brachycephalic patients with signs consistent with BOAS present a variable combination of upper airway resistance and dynamic airway compromise that cannot be understood without grasping its anatomical origin. The shortening of the facial skeleton, artificially selected over decades of breeding, has reduced the bony scaffold but not the soft tissues that occupy it: the nasal mucosa, soft palate, tongue and tonsils remain in a space that can no longer accommodate them (Liu et al., 2017).
The result is a multilevel obstruction documented with precision in the literature: stenotic nares, aberrant intranasal turbinates, elongated and hypertrophic soft palate, relative macroglossia and, in the most advanced cases, secondary laryngeal collapse (Krainer & Dupré, 2022). Liu et al. (2016) quantified using whole-body barometric plethysmography that nasal and oropharyngeal respiratory resistance in brachycephalic dogs is significantly greater than in mesocephalic breeds, even at rest and without physical exertion.
Figure 1. Anatomical components of BOAS — from conformation to functional obstruction (synthesis from published literature)
Reduction of the nasal aperture. Increases resistance to airflow at the first point of entry. Correlates with functional BOAS score in field studies (Lilja-Maula et al., 2024).
Intranasal bony growths that partially occlude the nasal passage. Frequent in Pugs and Bulldogs. Documented by CT in multiple case series (Krainer & Dupré, 2022).
The most studied component. Eivers et al. (2023) described histological changes in the soft palate tissue of brachycephalic dogs including muscle hypertrophy and oedema, contributing to dynamic obstruction during inspiration.
Chronic consequence of sustained intra-laryngeal negative pressure. Represents the final progression stage of BOAS. In these cases the surgical prognosis is more guarded (Krainer & Dupré, 2022).
Packer et al. (2015) established that the risk of BOAS increases continuously with the degree of brachycephaly, measured through the craniofacial ratio (CFR). In their study — considered a methodological reference in the field — the probability of functional BOAS exceeded 50% in dogs with a CFR below 0.20, a value characteristic of extreme Pugs and Bulldogs.
This progressiveness has direct implications for assessing flight risk: not all brachycephalic dogs have the same level of respiratory compromise. A Boston Terrier with wide nares and a non-elongated palate has a very different risk profile from a Pug with grade III BOAS. Airline policies, however, do not discriminate by individual severity: they classify by breed, introducing clinically significant variability that can only be resolved through individual veterinary assessment.
Rigas et al. (2024), in a cohort of more than 14,000 French Bulldogs, Pugs and English Bulldogs under primary veterinary care in the United Kingdom, documented that the prevalence of signs compatible with BOAS varies considerably by breed and diagnostic methodology. This variability reaffirms the impossibility of assigning a uniform risk level to all dogs of a given breed.
Commercial aircraft maintain a cabin pressure equivalent to an altitude of approximately 1,800 to 2,400 metres above sea level (approximately 565–750 mmHg), representing a reduction in the partial pressure of oxygen of the order of 15–20% relative to sea level. In a healthy normocephalic dog, this level of relative hypoxia is well tolerated through minor ventilatory adjustments. In a brachycephalic dog with pre-existing multilevel obstruction, the same hypoxia adds to an already compromised system.
Published evidence in human medicine has documented the effects of moderate altitude hypoxia in patients with upper airway obstruction; however, direct extrapolation of these findings to the canine species is not validated in the available veterinary literature. Specific data on the physiological response of brachycephalic dogs to cabin hypoxia under real aeronautical conditions are scarce. What is documented in veterinary studies is that animals with moderate to severe BOAS present increased upper airway resistance and ventilatory compromise even at rest and at sea level (Liu et al., 2016; Mitze et al., 2022). If a reduction in ambient PO₂ is added to that compromised baseline state, greater ventilatory demand would be expected on general physiological grounds; however, the clinical magnitude of that effect in flight has not been quantified in controlled studies with the species.
Dogs lack efficient sweat glands for dissipating body heat. Their primary thermoregulatory mechanism is panting — a process that depends on ventilation of the upper airway mucosa to facilitate evaporation and heat exchange. Davis, Cummings & Payton (2017) demonstrated that brachycephalic dogs are significantly less efficient at thermoregulation through this mechanism, and that the combination of brachycephaly and overweight further increases the difficulty.
In the context of air transport, this is relevant for two reasons. First, hold temperatures are not uniformly controlled during all phases of the flight, including loading and runway waiting. Second, the stress of transport per se increases metabolic heat production, demanding greater thermoregulatory efficiency precisely when the system is least able to provide it.
O'Neill, James et al. (2020), in an epidemiological study on heat-related illness episodes in dogs under primary veterinary care in the United Kingdom, identified over-representation of brachycephalic breeds — particularly English Bulldogs, French Bulldogs and Pugs — among documented cases. This study was conducted under terrestrial ambient conditions and does not address the aeronautical environment. Its relevance to the present analysis is indirect: the data suggest that these animals present reduced tolerance to thermoregulatory demands under heat conditions, which constitutes a plausible antecedent but not direct evidence of greater risk in the specific context of air transport.
Transport-associated stress — separation from the owner, unfamiliar environment, noise, vibration, confinement — activates the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system, with documented effects on heart rate, respiratory rate and tissue oxygen consumption. In a brachycephalic dog with diminished functional ventilatory reserve, the increase in metabolic demand induced by stress sharpens the discrepancy between oxygen supply capacity and tissue demand.
In a brachycephalic dog with pre-existing multilevel obstruction, the increase in metabolic demand induced by stress sharpens the discrepancy between oxygen supply capacity and tissue demand. Mitze et al. (2022), in their review of published clinical evidence on BOAS as a systemic problem, note that animals with moderate to severe forms may present signs consistent with chronic hypoxia; the authors reference prior primary evidence on haematological alterations in brachycephalic dogs, though the original studies quantifying these alterations are not within the scope of that review and exceed the bibliographic scope of this document. The assertion of chronic baseline hypoxia and elevated haematocrit as a consistent finding in the brachycephalic population should be understood, in the context of this analysis, as a description of what has been reported in recent clinical reviews, not as a primary datum verified in this document.
| Aeronautical factor | Mechanism in the brachycephalic dog | Differential: cabin vs hold |
|---|---|---|
| Reduced PO₂ (equivalent altitude 1,800–2,400 m) |
Greater respiratory effort on an already obstructed system; potential desaturation in individuals with severe BOAS | Equivalent in both compartments on modern aircraft with standard pressurisation; no verified difference in PO₂ |
| Temperature | Thermoregulatory demand via panting in a low-efficiency system (Davis et al., 2017) | Cabin: controlled temperature ~18–24°C. Hold: may vary during loading, runway waiting and on older aircraft types |
| Transport stress | ↑ HR, ↑ RR, ↑ O₂ consumption; aggravates supply/demand discrepancy in individuals with baseline hypoxia | Cabin: owner presence may reduce stress level. Hold: no visual or auditory contact with owner |
| Carrier confinement | Postural restriction; forced resting position may increase dynamic obstruction if neck extension is not permitted | Cabin: carrier under seat, owner access. Hold: sealed container, no access |
| Flight duration | Greater cumulative exposure to all preceding factors; relevant on long-haul routes | Both compartments equally affected by duration; the differential factor is access to supervision |
| Sources: Liu et al. (2016, 2017); Davis et al. (2017); Mitze et al. (2022); O'Neill et al. (2020). The "cabin vs hold" column reflects the general state of available knowledge; technical characteristics vary between aircraft types. | ||
The distinction between transport in the passenger cabin and transport in the cargo hold is the central axis of airline policies regarding brachycephalic dogs, and has technical justification. It is not purely an administrative distinction.
In the cabin, the animal travels in a carrier placed under the owner's seat, in a temperature-regulated environment and in direct presence of the responsible party, who can detect signs of respiratory distress in real time and intervene (alert crew, reposition the animal, open the carrier if the situation requires it). This capacity for continuous supervision is qualitatively different from the hold situation.
In the hold, the animal is in a container without visual or auditory contact with the owner. If a respiratory distress episode occurs, no one with clinical decision-making capacity has immediate access.
The United States Department of Transportation (DOT, 2024) animal incident reports, publicly accessible since 2005, document losses, injuries and deaths of animals during air transport on US carriers. Their review has been noted in the specialist literature as the instrument that motivated policy changes at North American airlines during the 2010–2020 decade regarding brachycephalic breeds. The raw data from these reports are available at transportation.gov/airconsumer; their detailed quantitative analysis exceeds the scope of this document and requires direct access to primary records for any claim of prevalence or proportion.
The IATA Live Animals Regulations (LAR, 2024) establish the international technical framework for the transport of animals on commercial aircraft, including specifications for containers, ventilation and minimum dimensions. The LAR constitute the technical basis on which each airline builds its specific operational policy. They do not themselves prohibit the transport of brachycephalic breeds, but do establish container requirements — including the requirement for additional space for these breeds in airlines that still accept them in the hold — that reflect the need to maximise ventilation (IATA, 2024).
Since 2005, US regulation (49 U.S.C. §41721; 14 C.F.R. Part 235) has required US commercial airlines operating aircraft with more than 60 seats to file monthly reports on incidents involving the loss, injury or death of animals during transport. These data are public and accessible on the DOT portal (transportation.gov). Their systematic review was the instrument that allowed the over-representation of brachycephalic breeds in adverse events to be identified, motivating policy changes at North American airlines during the 2010–2020 decade (DOT, 2024).
The FAA does not establish breed-specific restrictions for in-cabin transport on aircraft, but does regulate the general safety requirements applicable to pet containers and their stowage under the seat (FAA, 2023). Cabin temperature and pressurisation conditions are regulated by the FAA as part of the airworthiness standards of commercial aircraft.
| Airline | Hold (cargo) | Passenger cabin | Operational notes |
|---|---|---|---|
| LATAM Airlines | PROHIBITED | PERMITTED (weight+carrier limit) | Explicit list of breeds prohibited in hold includes Pug, Pekingese, Bulldog, Shih Tzu, Lhasa Apso, Boston Terrier, Boxer, Griffon, Shar Pei, Chow Chow, among others. Permitted in cabin if size and weight requirements are met. LATAM.com policy (2024). |
| Iberia | PROHIBITED / SEVERE RESTRICTION | PERMITTED (≤ 8 kg with carrier) | Brachycephalic breeds not accepted in hold. In cabin, combined weight of animal + carrier ≤ 8 kg. Policy consistent with IAG group. |
| Lufthansa | PROHIBITED since January 2020 | PERMITTED (≤ 8 kg total) | Hold ban in force since 1 January 2020. Breed list includes: Pug, Bulldog, Boston Terrier, Boxer, Griffon, Pekingese, Shih Tzu, Chow Chow, Shar Pei, among others. May be transported via Lufthansa Cargo as air freight under specific conditions. Source: Lufthansa.com (2024). |
| KLM | PROHIBITED (no exceptions for 4 most extreme breeds) | PERMITTED | English/French Bulldog, Boston Terrier and Pug: absolute hold ban. Other brachycephalic breeds: accepted in hold with one-size-larger carrier. In cabin with no breed restriction if dimensions are met. Source: KLM.com (2024). |
| Emirates | PROHIBITED | PROHIBITED since December 2020 | Permanent total embargo since December 2020 for all brachycephalic breeds in any compartment. One of the most restrictive policies in the industry. |
| British Airways | PARTIAL RESTRICTION | Assistance animals only | Does not accept Bulldogs, Pugs or Pekingese. Other brachycephalic breeds in hold with larger carrier. BA does not allow companion pets in cabin (only assistance animals). |
| United Airlines | PROHIBITED | PERMITTED | No brachycephalic breed accepted in hold. Cabin permitted if under-seat carrier requirements are met. Hold transport programme suspended since 2021 for most routes. |
| American Airlines | PROHIBITED | PERMITTED | Cargo programme fully suspended. Brachycephalic breeds accepted in cabin if size and weight requirements are met. |
| Delta Air Lines | PROHIBITED | PERMITTED | No brachycephalic breed in hold. Cabin: accepted under standard size conditions. Stable policy since 2018. |
| Sources: official airline websites, explorewithlora.com (cross-verification August 2025), PetTravel.com, Starwood Pet. Policies may change without notice. Always verify directly with the airline. This table does not constitute certification of current policy. | |||
The global pattern is consistent: the aviation industry trend is to prohibit hold transport of brachycephalic breeds and permit cabin transport under size and weight conditions, with notable exceptions (Emirates) that prohibit it in both compartments. This trend responds to accumulated incident data, not to arbitrary preference.
Given that BOAS is a continuum and not all brachycephalic breeds carry the same risk profile, evaluation of individual factors is essential to contextualise the risk of a specific flight for a specific animal.
The clinically weightiest factor. An animal with functional BOAS grade I has a very different profile from one with grade III with laryngeal collapse. Assessment using functional grading systems — such as that described by Liu et al. (2016) using plethysmography — allows severity to be objectified, though it is not always available in primary care settings.
Davis et al. (2017) documented that excess weight significantly increases thermoregulatory difficulty and respiratory burden in brachycephalic dogs. Liu et al. (2017) confirmed the association between higher body condition score and greater functional BOAS severity. An obese brachycephalic dog has a consistently higher flight risk than one at ideal weight.
Young animals — under 1 year — have airways still developing; geriatric animals may have accumulated secondary BOAS lesions (laryngeal collapse, systemic hypertension) that worsen the risk profile. Airlines establish minimum transport ages (generally 8–16 weeks) for reasons of physiological maturity.
Cumulative exposure to stress factors and reduced PO₂ increases with flight duration. Flights with stopovers present additional periods of loading, runway waiting and changing environmental conditions, especially during hold handling.
Hall, Carter & O'Neill (2022) documented that heat-related illness episodes in high-risk breeds show marked seasonality, with peaks during months of higher temperature. Tarmac heat during loading and pre-departure waiting represents an additional risk factor in summer or on tropical routes.
Animals that have undergone corrective BOAS surgery (rhinoplasty, palatoplasty) may present an improved risk profile relative to their pre-operative state, although the literature does not allow precise quantification of the magnitude of this improvement in the specific context of air transport.
Description of practices — not prescriptive or individualised
Pre-flight veterinary assessment of a brachycephalic dog aims to document the animal's baseline respiratory status, identify modifiable risk factors and provide the owner with the information needed for an informed decision. It is not an administrative formality.
In published clinical practice, pre-flight assessment of brachycephalic animals has included evaluation of resting respiratory rate and effort, auscultation of the upper airway and thorax, evaluation of body condition and weight, and review of the clinical history for previous episodes of respiratory distress, syncope or BOAS signs. Lilja-Maula et al. (2017) described a clinical grading system that in their study context was supplemented with exercise tests to objectify the functional severity of BOAS. The description of these components reflects what is documented in the literature; their application in each specific case is the exclusive decision of the responsible veterinarian and cannot be derived from this document.
Some airlines and organisations such as IPATA have developed Brachycephalic Fit-To-Fly assessments, the objective of which is to discriminate, within the "brachycephalic breed" category, individuals with severe BOAS that contraindicate flight from those with mild-to-moderate compromise in which risk can be managed. These assessments have not been universally adopted by airlines.
Brachycephalic dogs present a physiology that can be compromised by the conditions of the aeronautical environment — reduced PO₂, variable temperature, stress and confinement — proportionally more so than normocephalic breeds. This differential risk is not uniform within the group: it depends on individual BOAS severity, body condition, age, flight duration and the capacity for supervision during transport.
The global airline trend — prohibiting hold transport and permitting cabin transport under controlled conditions — reflects precisely this risk asymmetry between the two compartments: the cabin offers direct supervision and regulated temperature; the hold does not. This is not a perfect response to the problem, but it is one with coherence with the available evidence.
The scientific literature does not contain a well-founded prohibition on air transport of all brachycephalic breeds under all conditions. What does exist is an evidence base that justifies differentiated caution, individual assessment and a systematic approach that considers the specific animal, airline, route and travel conditions.