Heatstroke in flat-faced dogs: which breeds are at risk

Flat-faced dogs are at higher risk of heatstroke because their skull shape can cause upper-airway abnormalities that make panting, a dog's main way of cooling down, less effective. In a UK study of 905,543 dogs, flat-faced (brachycephalic) dogs had 2.10 times the odds of heat-related illness of medium-skulled dogs, and Bulldogs, French Bulldogs and Pugs each had clearly higher odds than Labradors. The result was not the same for every flat-faced breed, as the sections below explain.

If you think your dog has heatstroke, this is an emergency. The Merck Veterinary Manual says signs include hot skin, vomiting, drooling, rapid panting, distress, uncoordinated movement, collapse or unconsciousness. VCA Animal Hospitals adds dry or sticky gums, abnormal gum colour, bruising in the gums, lethargy, disorientation and seizures. Move the dog out of the heat and take it to a vet right away. Heatstroke can kill: in the UK study, 14.18% of confirmed heat-related illness events were fatal.

Why are flat-faced dogs more prone to heatstroke?

Dogs cannot cool themselves by sweating the way people do. VCA explains that dogs have a relatively small number of sweat glands, in their footpads, and that panting is their primary way of regulating body temperature. Cornell says the same.

According to VCA, flat-faced dogs have skull bones shortened in length, which gives the face a pushed-in appearance and alters the soft tissues the bones support. Some of the changes cause breathing problems, together called brachycephalic obstructive airway syndrome (BOAS). VCA lists abnormally narrow nostrils, a soft palate too long for the mouth that partly blocks the entrance to the windpipe, a windpipe narrower than normal, collapse of the voice box cartilage, and small pouches in the voice box that turn outward or get sucked into the airway. Cornell says some or all of these can be present in one dog, causing varying degrees of breathing difficulty, and that the syndrome is seen most often in the English Bulldog, Pug, French Bulldog and Boston Terrier.

Mildly affected dogs have noisy breathing, especially with exercise, and most snort when excited and snore when relaxed, VCA says. Severely affected dogs tire easily and may collapse or faint after exercise. Signs are often worse in hot or humid weather, and affected dogs are more prone to overheating because their ability to pant and cool themselves is compromised. The authors of the large UK study give the same mechanism: the surface area of the nasal turbinates and effective ventilation allow heat to be lost by evaporation during panting, so flat-faced dogs have reduced ways of getting rid of heat (Hall et al. 2020).

One study tested this. Davis and colleagues exposed 52 flat-faced and 53 other healthy dogs to a cool treatment (about 21.8 °C, 62% relative humidity) and then a hot one (about 32.9 °C, 52% relative humidity), measuring breathing in a sealed whole-body plethysmograph. Flat-faced dogs had a greater increase in breathing rate in response to the heat, and the authors concluded they have a decreased capacity for thermoregulation (Davis et al. 2017, abstract).

Which flat-faced breeds have the highest heatstroke risk?

The largest study used VetCompass, a database of electronic records from UK vets. It covered 905,543 dogs in 2016 and found 395 confirmed heat-related illness events in 390 dogs (Hall et al. 2020). The illness was uncommon, affecting 0.04% of dogs, but 56 of the 395 events ended in death, a fatality rate of 14.18% (95% range 11.08 to 17.96). Of the 54 deaths where the manner was recorded, 35 were by euthanasia and 19 were unassisted.

Flat-faced dogs had 2.10 times the odds of heat-related illness of medium-skulled dogs (95% range 1.68 to 2.64). Long-skulled dogs showed no significant difference. Flat-faced breeds overall had an incidence of 0.08%, against 0.04% for all dogs.

The study compared each breed with the Labrador Retriever, the most common breed in the data after crossbreds. That makes the Labrador a yardstick, not a claim that Labradors carry no risk. An odds ratio compares groups of dogs in records: a ratio of 14 means odds about 14 times those of the comparison group. It is not the chance for any single dog.

Breed (compared with Labrador)	Odds ratio	95% range	Clear result?
Chow Chow	16.61	6.21 to 44.44	Yes
Bulldog	13.95	8.01 to 24.29	Yes
French Bulldog	6.49	3.62 to 11.63	Yes
Dogue de Bordeaux	5.31	1.99 to 14.21	Yes
Greyhound	4.26	1.88 to 9.70	Yes
Cavalier King Charles Spaniel	3.45	1.86 to 6.42	Yes
Pug	3.24	1.67 to 6.29	Yes
English Springer Spaniel	2.74	1.25 to 6.01	Yes
Golden Retriever	2.65	1.40 to 5.01	Yes
Boxer	2.26	0.95 to 5.34	No
Shih Tzu	0.47	0.18 to 1.24	No

Nine breeds had clearly higher odds. The authors name five of them as flat-faced: Bulldog, French Bulldog, Dogue de Bordeaux, Cavalier King Charles Spaniel and Pug. The other four were the Chow Chow, Greyhound, English Springer Spaniel and Golden Retriever, so heat illness is not only a flat-faced problem. The authors say the Chow Chow's range is very wide because of a relatively small sample, and that the Golden Retriever's thicker coat may be the tipping factor between it and the Labrador.

Do all flat-faced breeds have the same risk?

No. The authors report that the Lhasa Apso, Shih Tzu and Chihuahua had the lowest odds of the breeds analysed, even though the authors classify all three as flat-faced. None was a statistically clear result: the Shih Tzu's odds were 0.47 (range 0.18 to 1.24), the Chihuahua's 0.44 (0.17 to 1.18) and the Lhasa Apso's 0.24 (0.03 to 1.76).

The Boxer sits on the other side. The authors say it trended towards increased odds (2.26), but the range (0.95 to 5.34) includes 1, so the result is not clear. Crosses with a flat-faced breed had the lowest incidence of any skull-shape group, but not a significantly lower odds ratio (0.22, range 0.03 to 1.56); the authors suggest this may reflect the group being comparatively young and lighter.

A range that includes 1 means the study could not tell whether a breed is at higher or lower risk. "Not clear" does not mean "safe", and breeds with few cases give wide ranges.

Skull shape and survival. A follow-up VetCompass analysis of 856 events from 2016 to 2018 found that skull shape was not associated with whether a dog became severely ill, but it was associated with dying. In the final model, which also accounted for severity grade and age, flat-faced dogs had 3.01 times the odds of death of medium-skulled dogs (range 1.60 to 5.67). The authors conclude that the risk of death was greater for dogs with reduced capacity to thermoregulate, meaning older and flat-faced dogs (Hall et al. 2022).

Does hot, humid weather make it worse?

A Texas A&M College of Veterinary Medicine article says that as humidity increases, evaporation and the resulting heat exchange decrease, and that once humidity reaches about 85 percent, evaporative cooling is almost totally inhibited. Cornell says dogs are most at risk if they exercise in hot and humid weather.

For flat-faced dogs, VCA says signs of heat stroke can occur when the outside temperature and humidity are only moderately elevated. The Merck Veterinary Manual says some breeds, especially short-nosed breeds, can overheat from stress or excitement even on cool days.

The 2016 UK study's risk model did not include weather, and its authors note that a prediction model would need ambient temperature, humidity, activity levels, fitness and hydration. It shows which dogs are at higher risk, not the temperature at which a flat-faced dog becomes unsafe. None of the sources read for this article reports data on dogs in India.

News reports on India Meteorological Department warnings give some context for Kerala. Onmanorama reported a yellow warning for hot and humid weather from 7 to 9 April 2026, with maximum temperatures around 38 °C in isolated areas of Palakkad, and that the advice included not leaving children or pets in parked vehicles. A later report stated that Kerala's high humidity amplifies the felt temperature. These are news reports, not veterinary evidence.

How can I lower my flat-faced dog's heatstroke risk?

Keep the weight healthy. In Davis's study, body condition score was positively associated with body temperature regardless of environmental conditions or breed type, and was a greater determinant of body temperature than breed type. In the UK data, dogs at or above the average bodyweight for their breed and sex had 1.42 times the odds of heat-related illness (range 1.12 to 1.80), and the authors called a healthy bodyweight an important management tool. For feeding by weight and age, see the Pug diet chart and calculator and the index of breed diet charts.

Follow the airway advice. For mild cases, Cornell lists a healthy weight, minimising panting, avoiding excessive heat and humidity, controlled activity, minimising stress and using a harness instead of a neck collar. Cornell says more severe cases need surgical correction, and earlier intervention gives better outcomes. A vet can assess an individual dog.

Avoid the main heatstroke situations. Cornell advises never leaving a dog in a car unattended, avoiding strenuous exercise in hot and humid weather, providing shade and water, avoiding walks in the hottest part of the day and staying indoors during extreme heat and humidity. VCA says leaving a dog in a car with inadequate ventilation is the most common cause of heat stroke, and that body temperature can rise very rapidly, often within minutes.

This article is general education, not veterinary advice. See the disclaimer and the editorial policy.

Frequently asked questions

Are Pugs more likely to get heatstroke than other dogs?

In the UK VetCompass study, Pugs had 3.24 times the odds of heat-related illness of Labradors (95% range 1.67 to 6.29), a clearly raised result. Cornell lists Pugs among the breeds in which the airway syndrome is seen most often. These figures describe groups of dogs, not the chance for an individual Pug.

Can a flat-faced dog get heatstroke on a cool day?

The Merck Veterinary Manual says some breeds, especially short-nosed breeds, can overheat from stress or excitement even on cool days. VCA says signs of heat stroke in flat-faced dogs can occur when the outside temperature and humidity are only moderately elevated. Merck says heat stroke is an emergency.

What are the signs of heatstroke in a Pug or Bulldog?

The Merck Veterinary Manual lists hot skin, vomiting, drooling, rapid panting, distress, uncoordinated movement, collapse and unconsciousness. VCA lists elevated breathing rates, dry or sticky gums, abnormal gum colour, bruising in the gums, lethargy, disorientation and seizures. Merck says to take the pet to the vet right away.

Does extra weight raise a flat-faced dog's heatstroke risk?

In a study of 105 healthy dogs, body condition score was linked to higher body temperature in cool and hot conditions, and was a greater determinant of body temperature than breed type (Davis et al. 2017). In the UK data, dogs at or above their breed and sex average weight had 1.42 times the odds of heat-related illness. Cornell lists overweight as a heatstroke risk factor.

Sources

• Hall et al. (2020), Scientific Reports 10:9128. https://doi.org/10.1038/s41598-020-66015-8
• Hall et al. (2022), Veterinary Sciences 9(5):231. https://doi.org/10.3390/vetsci9050231
• Davis et al. (2017), JAVMA 251(10):1160. https://doi.org/10.2460/javma.251.10.1160
• VCA, brachycephalic airway syndrome. https://vcahospitals.com/know-your-pet/brachycephalic-airway-syndrome-in-dogs
• VCA, heat stroke in dogs. https://vcahospitals.com/know-your-pet/heat-stroke-in-dogs
• Cornell, BOAS. https://www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-topics/brachycephalic-obstructive-airway-syndrome-boas
• Cornell, heatstroke. https://www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-information/heatstroke-medical-emergency
• Merck Veterinary Manual, dog or cat emergency. https://www.merckvetmanual.com/special-pet-topics/emergencies/what-to-do-in-a-dog-or-cat-emergency
• Texas A&M (2020). https://vetmed.tamu.edu/news/pet-talk/hot-topic-keeping-your-pet-safe-as-temperatures-rise
• Onmanorama, 7 April 2026. https://www.onmanorama.com/news/kerala/2026/04/07/kerala-heatwave-warning.html
• Onmanorama, 23 April 2026. https://www.onmanorama.com/news/kerala/2026/04/23/kerala-heatwave-warning-palakkad-thrissur-kollam.amp.html