Dogs in a heatwave: recognising heatstroke, what to do, how to prevent it

Every summer, vets in France see a stream of dogs arriving in respiratory distress, overheated, sometimes unconscious. A heatwave is not just uncomfortable for our four-legged companions: it is a life-threatening emergency, with real mortality, documented by the most recent veterinary studies. Here is what science says about heatstroke in dogs — and how to save your dog's life.

Why are dogs so vulnerable to heat?

Unlike humans, dogs do not have sweat glands all over their body. Their temperature regulation relies almost entirely on three very limited mechanisms:

• Panting: it gets rid of heat through evaporation from the tongue and upper airways. Very effective in dry air, it stops working once humidity goes above 70%.
• Paw pads: the only part of the body with a few sweat glands. Their tiny surface area limits their effect.
• Skin vasodilation: a little heat escapes through the skin, but a thick coat (and the undercoat in Nordic breeds) blocks this transfer.

The result: a dog's normal body temperature (38–39 °C) can climb within a few minutes during exercise in the heat, or when shut in an overheated space.

Heatstroke: thresholds and effects on the body

Understanding the temperature stages is essential to judge how urgent it is:

• 38–39 °C: normal temperature.
• 39.5–40.5 °C: moderate hyperthermia. The dog pants heavily and looks for shade.
• 40.5–41.5 °C: established heatstroke. Risk of multiple organ failure.
• > 42 °C: damage to the brain, kidneys and liver, disseminated intravascular coagulation (DIC). Rapid death without intervention.

Above 41 °C sustained for more than 30 minutes, the body's cell proteins denature, just like egg white cooking. The damage to some organs is irreversible.

The figures: very real mortality

The most recent veterinary studies document high mortality from heatstroke in dogs:

• A major Royal Veterinary College study (Hall et al. 2020, Scientific Reports) of 905 cases of canine heatstroke in the UK reports a mortality rate of 14.2%.
• The landmark Israeli study Bruchim et al. 2006 (JAVMA) of 54 dogs with severe hyperthermia found a mortality of 50% when heatstroke was diagnosed late.
• The time between the first signs and the start of cooling is the single most important factor for the outcome.
• Contrary to popular belief, Hall et al. 2020 shows that parked cars account for only 13% of cases: most heatstroke happens during physical activity in hot weather (74% of cases).

High-risk breeds and profiles

Not all dogs cope equally with heat. Risk factors identified by the RVC's VetCompass programme:

• Brachycephalic (flat-faced) breeds: French Bulldog, Pug, English Bulldog, Boxer, Cavalier King Charles Spaniel. Their airway anatomy makes panting ineffective. Risk 2 to 3 times higher.
• Overweight or obese dogs: fat insulation makes hyperthermia worse. Risk twice as high.
• Older dogs (> 8 years): reduced heart, lung and temperature-regulating capacity.
• Puppies under 6 months: immature temperature regulation.
• Long-haired or thick-coated breeds: Husky, Malamute, Pyrenean Shepherd, Newfoundland.
• Black dogs: absorb more of the sun's radiation.
• Dogs with an existing heart or respiratory condition.

Recognising the signs: the severity scale

Heatstroke progresses in stages. Learn to recognise them:

Stage 1 — Warning (temp. 39.5–40.5 °C):

• Heavy, noisy panting, tongue hanging far out.
• Excessive drooling.
• The dog looks for shade and refuses to keep walking.
• Gums redder than usual.

Stage 2 — Emergency (temp. 40.5–41.5 °C):

• Ragged, noisy, sometimes painful panting.
• Bright red gums, then turning purple.
• Vomiting, sometimes bloody diarrhoea.
• Staggering, muscle weakness.
• Very fast, weak heartbeat.

Stage 3 — Life-threatening (temp. > 41.5 °C):

• Seizures.
• Loss of consciousness.
• Bleeding (gums, anus, urine).
• Cardiac and respiratory arrest imminent.

What to do in an emergency — minute by minute

Every minute counts. The outcome depends directly on how fast the dog is cooled. Follow this protocol endorsed by the British Veterinary Association:

Minutes 0–2: get out of the heat

• Move the dog to a cool, shady place (ideally air-conditioned).
• Lay it on its side and remove its collar and harness.

Minutes 2–15: active cooling

• Wet the dog with cool water at 15–20 °C (NOT ice-cold — water that is too cold causes vasoconstriction, which makes internal overheating worse).
• Focus on areas with lots of blood vessels: neck, armpits, groin, belly, paw pads.
• Keep the air moving with a fan or by fanning by hand.
• Offer small sips of water if the dog is conscious (never force it).

Minute 15+: getting to the vet is ESSENTIAL

• Even if the dog seems better, get to the vet as fast as you can. Internal damage (kidneys, liver, blood clotting) can appear 24–72 hours after the episode.
• Keep cooling on the way with damp cloths.
• Call the practice to let them know you are coming.

⚠️ NEVER: immerse the dog in ice-cold water (thermal shock), give aspirin, or force an unconscious dog to drink.

The persistent myth of the car “in the shade, windows open a crack”

The car remains one of the deadliest traps — and one of the most avoidable. Experimental measurements leave no doubt:

• On a 22 °C day, a car parked in the sun reaches 47 °C in 60 minutes (AVMA / Stanford study).
• On a 30 °C day, the inside of the car exceeds 50 °C in 30 minutes, even with the windows open a crack.
• Simply parking in the shade only slows this down by a few minutes: the sun moves and so does the shade.

The absolute rule: never leave an animal alone in a parked vehicle, whatever the season, time of day or duration. Not even for five minutes to pop into the shops.

The underestimated danger of tarmac

Tarmac acts like a radiator. When the air is 30 °C, the road surface can exceed 55 to 65 °C in full sun. At that temperature, a dog's paw pads — walking barefoot on the surface — suffer deep burns within seconds.

The 7-second test: place the back of your hand on the tarmac for 7 seconds. If you can't, your dog can't walk on it either. Go out early in the morning (before 8 am) or late in the evening (after 9 pm), sticking to grassy, shady surfaces.

10 golden rules to get through a heatwave safely

1. Fresh water at all times, always available and refreshed several times a day. Add ice cubes.
2. Several shady spots in the garden, and constant access to a cool indoor space.
3. No walks between 11 am and 6 pm during a heatwave alert.
4. The 7-second tarmac test before every walk.
5. No intense exercise (jogging, cycling, ball games) when temperatures peak.
6. Watch brachycephalic breeds and at-risk dogs extra closely.
7. Cooling mats and damp towels available in the rooms where your dog rests.
8. No animal in a parked car, EVER, under any circumstances.
9. Regular brushing to remove the dead undercoat and help air reach the skin.
10. In France, check Météo France's weather alerts: vigilance.meteofrance.fr and Santé Publique France's heatwave plan.

Conclusion: prepare for the heatwave

Heatstroke in dogs is not inevitable: it is almost always preventable. Recent studies remind us that 87% of cases happen outside a car — on a walk that goes on too long, during exercise in the sun, or when shut in a poorly ventilated room. Prevention rests on three pillars: know your dog (at-risk breeds, other health conditions), anticipate the conditions (weather alerts such as Météo France's in France) and act fast at the first signs. Fifteen minutes of properly done cooling can make the difference between life and death.