Dogs cannot cool themselves through sweat glands the way humans do; they dissipate body heat primarily through panting and, secondarily, through radiation and convection (Bruchim et al., 2017). For this reason, when ambient temperature and humidity rise or during intense exercise, heat production can exceed the capacity to shed it, and heatstroke develops. Heatstroke is a life-threatening veterinary emergency that can progress to multi-organ damage. This article examines the signs of heatstroke, the first aid an owner can provide, and which dogs are at greater risk, in the light of current scientific literature.
Emergency Signs — Don't Lose Time
Heavy, noisy breathing, excessive drooling, vomiting, bloody diarrhea, weakness, confusion or disorientation, seizures, and collapse are signs of severe heatstroke (Cornell Riney Canine Health Center; Bruchim et al., 2017). If you see these signs, begin cooling the dog immediately and reach a veterinarian urgently.
1. What Is Heatstroke, and Why Are Dogs Vulnerable?
Dogs have no functional sweat glands; they shed more than 70% of their body heat through radiation and convection, and the remainder through evaporation via panting (Bruchim et al., 2017). These mechanisms become inadequate when ambient temperature approaches body temperature or when humidity is high. When the heat load exceeds the capacity to dissipate it, body temperature rises to dangerous levels and cellular-level damage begins. Despite early cooling and supportive care, mortality in severe cases is approximately 50% (Bruchim et al., 2017).
2. How Common and Deadly Is It?
In United Kingdom primary-care veterinary data (2016), the incidence of heatstroke among 905,543 dogs was 0.04%, with a case fatality rate of 14.18% (Hall et al., 2020a). In the emergency-care data from 2022, the country's hottest year on record, the incidence rose to 0.23% and the event fatality rate to 26.56% (Beard et al., 2024). This increase shows that the burden of heatstroke is growing alongside a warming climate and that prevention is becoming ever more important.
3. A Common Misconception: Heatstroke Doesn't Happen Only in "Hot Cars"
In public perception, heatstroke is most often identified with dogs left forgotten in vehicles. Yet the data show the opposite: of the UK cases with a known trigger, 74.2% were exercise-related (exertional) and only 5.2% were associated with confinement inside a vehicle (Hall et al., 2020b). In other words, a run, a game, or an intense walk on a hot day is the biggest trigger. The same risk pattern has also been independently confirmed in the Australian population (Tripovich et al., 2023).
4. Which Dogs Are at Greater Risk?
Heatstroke can affect any dog, but some dogs are markedly more vulnerable (Hall et al., 2020a; 2022):
| Risk Factor | Finding |
|---|---|
| Brachycephalic (short-nosed) conformation | 2.10 times higher risk than mesocephalic dogs (Hall et al., 2020a) |
| High-risk breeds | Chow Chow, Bulldog, French Bulldog, Dogue de Bordeaux, Greyhound, Pug (Hall et al., 2020a) |
| Body weight | Risk increases in dogs over 50 kg (Hall et al., 2020a) |
| Advanced age | ≥12 years, 8.87 times the risk of a fatal course (Hall et al., 2022) |
The anatomical reason for the elevated risk in brachycephalic dogs is the upper airway obstruction (brachycephalic obstructive airway syndrome, BOAS) caused by their short skull conformation. Increased airway resistance and a reduced evaporative surface impair heat dissipation through panting (Packer et al., 2015). Surgical correction has been shown to improve the heat response to exercise, which supports this mechanism (Žgank et al., 2023).
5. Signs: Three Grades of Severity
According to the VetCompass clinical grading tool (856 cases), the most frequent findings are respiratory change (68.7%) and lethargy (47.8%) (Hall et al., 2021). The signs are divided into three grades:
| Grade | Findings | Fatality rate |
|---|---|---|
| Mild | Respiratory change, lethargy | 2.2% |
| Moderate | Digestive signs (vomiting/diarrhea), single seizure, episodic collapse | intermediate value |
| Severe | Neurological impairment, gastrointestinal bleeding, coagulation disorder | 56.8% |
The difference in fatality between mild and severe cases (2.2% versus 56.8%) clearly demonstrates why early diagnosis saves lives (Hall et al., 2021).
6. First Aid: "Cool First, Transport Second"
Survival is 97% in mild cases and 43% in severe heatstroke. For this reason, active cooling should be started on the spot, before taking the dog to the clinic (Royal Veterinary College, 2021). Recommended cooling methods (Hall et al., 2023):
- Young and healthy dogs: immersion in cold water is the most effective method.
- Older or unwell dogs: evaporative cooling by pouring water over the dog and providing airflow (fan/air conditioning) is preferred.
In the field, only 24% of dogs are cooled with the recommended method, while 51% are treated with the less effective wet-towel method (Hall et al., 2023). Applying the correct method changes the outcome.
Limit: This section covers only the first-aid cooling that an owner can perform. Decisions about medication, fluid therapy, and dosage belong to the veterinarian. Once you have started cooling, get the dog to a veterinary clinic without delay.
7. Why Can It Be Fatal?
Heatstroke can progress to multi-organ damage in the kidneys, liver, digestive system, and cardiovascular system, and to disseminated intravascular coagulation (DIC) (Bruchim et al., 2009). In hospitalized dogs, acute kidney injury, DIC, and neurological impairment are the principal complications that determine survival; biomarkers such as serum heat shock protein 72 (HSP72) may carry prognostic value (Bruchim et al., 2016). This picture makes clear why early and correct intervention is critical.
8. Prevention
- Restrict exercise during hot and humid hours; move walks to the early morning or late evening.
- Provide constant shade and fresh drinking water; never leave a dog in a parked vehicle.
- Minimize heat exposure in brachycephalic, older, and obese dogs.
- Support cooling and adequate water intake; daily water needs vary with the animal's body weight.
VetKriter Daily Water Requirement Calculator
Calculate your dog's daily water requirement based on its body weight; during hot periods, adequate water intake is the first line of defense against heat stress.
Calculate Water Requirement9. References
- Beard, S., Hall, E. J., Bradbury, J., Carter, A. J., Gilbert, S., & O'Neill, D. G. (2024). Epidemiology of heat-related illness in dogs under UK emergency veterinary care in 2022. Veterinary Record, 194(11), e4153.
- Bruchim, Y., Horowitz, M., & Aroch, I. (2017). Pathophysiology of heatstroke in dogs – revisited. Temperature, 4(4), 356-370.
- Bruchim, Y., Loeb, E., Saragusty, J., & Aroch, I. (2009). Pathological findings in dogs with fatal heatstroke. Journal of Comparative Pathology, 140(2-3), 97-104.
- Bruchim, Y., Segev, G., Kelmer, E., Codner, C., Marisat, A., & Horowitz, M. (2016). Hospitalized dogs recovery from naturally occurring heatstroke; does serum heat shock protein 72 provide a prognostic biomarker? Cell Stress and Chaperones, 21(1), 123-130.
- Cornell University College of Veterinary Medicine, Riney Canine Health Center. (n.d.). Heatstroke: A medical emergency.
- Hall, E. J., Carter, A. J., & O'Neill, D. G. (2020a). Incidence and risk factors for heat-related illness (heatstroke) in UK dogs under primary veterinary care in 2016. Scientific Reports, 10, 9128.
- Hall, E. J., Carter, A. J., & O'Neill, D. G. (2020b). Dogs don't die just in hot cars – Exertional heat-related illness (heatstroke) is a greater threat to UK dogs. Animals, 10(8), 1324.
- Hall, E. J., Carter, A. J., Bradbury, J., Barfield, D., & O'Neill, D. G. (2021). Proposing the VetCompass clinical grading tool for heat-related illness in dogs. Scientific Reports, 11(1), 6828.
- Hall, E. J., Carter, A. J., Chico, G., Bradbury, J., Gentle, L. K., Barfield, D., & O'Neill, D. G. (2022). Risk factors for severe and fatal heat-related illness in UK dogs – A VetCompass study. Veterinary Sciences, 9(5), 231.
- Hall, E. J., Carter, A. J., Bradbury, J., Beard, S., Gilbert, S., Barfield, D., & O'Neill, D. G. (2023). Cooling methods used to manage heat-related illness in dogs presented to primary care veterinary practices during 2016–2018 in the UK. Veterinary Sciences, 10(7), 465.
- Packer, R. M. A., Hendricks, A., Tivers, M. S., & Burn, C. C. (2015). Impact of facial conformation on canine health: Brachycephalic obstructive airway syndrome. PLOS ONE, 10(10), e0137496.
- Royal Veterinary College. (2021). The RVC urges owners of hot dogs to "cool first, transport second".
- Tripovich, J. S., Wilson, B., McGreevy, P. D., & Quain, A. (2023). Incidence and risk factors of heat-related illness in dogs from New South Wales, Australia (1997–2017). Australian Veterinary Journal, 101(12), 490-501.
- Žgank, Ž., Nemec Svete, A., Lenasi, H., Vodičar, J., & Erjavec, V. (2023). The effect of the surgical treatment of brachycephalic obstructive airway syndrome on the thermoregulatory response to exercise in French bulldogs: A pilot study. Frontiers in Veterinary Science, 10, 1229687.