Dog Heatstroke: Signs, First Aid and Prevention

By INVIROX Training Team · Published 2026-10-20 · 7 min read

Why dogs overheat faster than people

Dogs have very few sweat glands, essentially limited to their paw pads. Their main cooling mechanism is panting, which moves air over wet surfaces in the mouth and airway to lose heat by evaporation.

That system works well in dry moving air and poorly in humidity, because evaporation slows when the surrounding air is already saturated. It is why a humid 26 degree day can be more dangerous than a dry 30 degree one, and why owners are frequently caught out by weather that does not feel extreme.

It also means a dog cannot cool down while continuing to exert themselves. A dog who is running is generating heat faster than panting can remove it, and a dog who will not stop, which describes most retrievers with a ball, is a dog who will keep going past the point of safety.

The signs, in the order they appear

The gum colour is the most useful single check most owners never make. Lift the lip: healthy gums are pale pink and moist. Brick red gums mean the dog is struggling to shed heat. Pale, grey or blue means circulatory trouble and is a critical emergency.

First aid, the first ten minutes

What you do in the first few minutes matters more than almost anything that happens afterwards.

1. Stop everything and get the dog into shade or, better, indoors with air moving.
2. Pour or spray cool water over them, concentrating on the neck, armpits, groin and paws where blood vessels run close to the surface.
3. Keep air moving over the wet coat. A fan, an open car window, or simply fanning with anything to hand.
4. Offer small amounts of cool water to drink. Do not force it and do not let them gulp a large volume at once.
5. Call the vet and start travelling. Continue cooling in the car with the windows down or air conditioning on.
6. Do not stop cooling because they seem better. Internal temperature lags behind appearance.

Current veterinary guidance favours cool water rather than ice water, and specifically advises against packing a dog in ice. Very cold water on the skin can constrict surface blood vessels and slow heat loss from the core, which is the opposite of what you need.

Every dog who has shown more than early signs needs to be seen by a vet even if they appear to recover. Heatstroke causes internal damage that presents hours later, and the dog who looks fine in the car can be in serious trouble that evening.

The dogs at highest risk

• Flat-faced breeds. Bulldogs, French Bulldogs, Pugs and Boxers have compromised airways and overheat dramatically faster than other dogs.
• Thick double-coated breeds, particularly northern types in warm climates.
• Overweight dogs, for whom the same activity generates more heat.
• Very young and very old dogs, whose temperature regulation is less efficient.
• Dogs with heart or airway conditions.
• Dark-coated dogs in direct sun.
• Any dog who will not self-regulate, which describes most ball-obsessed retrievers and working breeds.

The last item deserves emphasis because it cuts across the others. A fit young Labrador in perfect condition is at high risk precisely because they will keep chasing a ball long after they should have stopped. With those dogs, the owner has to be the off switch.

→ Related reading: matching activity to the dog and the day

Prevention is almost entirely timing

Nearly every case is preventable, and the prevention is unglamorous.

1. Walk early and late. On a warm day, before eight in the morning and after eight in the evening, and skip the middle entirely.
2. Test the pavement with the back of your hand for seven seconds. If you cannot hold it there, it is too hot for paws.
3. Carry water on every warm walk, and offer it more often than you think is necessary.
4. Cut the duration and the intensity, not just one of them. A short walk at a fast pace is still a lot of heat.
5. Provide deep shade and a heavy water bowl that cannot be knocked over in the garden.
6. Never leave a dog in a car, even briefly, even with windows cracked, even in the shade.

Humidity deserves its own line. Check it alongside temperature, because a humid day in the low twenties can be more dangerous than a dry day considerably warmer, and most people only look at the temperature.

→ Related reading: training through a hot summer

Cooling equipment, honestly assessed

The shaving row is the one people get wrong most often with good intentions. A double coat provides insulation in both directions and protects skin from sun. Removing it on a Husky or a Golden Retriever generally makes them hotter rather than cooler, and regular de-shedding of the undercoat is the better answer.

→ Related reading: managing a double coat properly

Cars, and the number that matters

This gets its own section because it remains the most common way dogs die of heat, and because the numbers are worse than people believe.

On a 22 degree day, the interior of a parked car can exceed 45 degrees within an hour, with most of that rise happening in the first twenty to thirty minutes. Parking in shade slows it and does not prevent it, because shade moves. Cracking the windows makes very little difference.

There is no safe duration and no safe version of this. If the dog cannot come with you, they stay at home.

If you find a dog in a car showing signs of distress, call the police or the relevant emergency service rather than acting alone, and stay with the vehicle until someone arrives.

After a heat incident

A dog who has had heatstroke once is more susceptible afterwards, which changes how you manage the rest of the summer.

• Follow the vet's guidance on rest, which is usually several days of very light activity.
• Watch for delayed signs over the following forty-eight hours: lethargy, appetite change, dark urine, continued vomiting.
• Be considerably more conservative for the rest of the season.
• Expect a lower heat tolerance going forward and plan walks accordingly.
• Mention the episode at every future vet visit, because it is relevant history.

The reassuring part is that dogs who are cooled early and treated promptly usually recover fully. The determining factor is almost always how quickly cooling started, which is why knowing the first ten minutes is worth more than knowing anything else in this article.