Dog Heatstroke: Why "Never Use Cold Water" Is Wrong

Heatstroke kills dogs in Hong Kong every summer. And the single most repeated piece of first aid advice online, "never use cold water, cool them slowly with tepid water", is wrong.

In this article

• Why Hong Kong humidity makes heatstroke worse
• What are the signs, and which ones mean go now?
• Dog heatstroke first aid: the first 10 minutes
• Three things that make it worse
• Which dogs are most at risk?
• How do I prevent heatstroke?
• Frequently asked questions

Why Hong Kong humidity makes heatstroke worse

Dogs shed heat mainly by panting, and panting only works because moisture evaporates. It is the same reason you feel cooler when a breeze hits damp skin.

That is the problem here. When the air is already close to saturated, very little evaporates, so a dog can pant hard and still shed almost no heat. In Hong Kong, 30°C at 85% humidity is considerably more dangerous for a dog than 33°C in dry air. The thermometer will not tell you that.

Dogs also cannot sweat the way we do. There are a few sweat glands in the paw pads and they contribute very little. So a day you would describe as "not that bad" can already be past what your dog can handle.

What are the signs, and which ones mean go now?

The early signs get mistaken for an ordinary tired dog. Telling them apart from the emergency signs is often the whole difference.

Clinically, a rectal temperature above 40°C is treated as heatstroke, and above 41.1°C organ damage becomes a real risk. Use a pet thermometer if you own one. If you do not, do not delay cooling in order to find one.

Dog heatstroke first aid: the first 10 minutes

RVC research into heatstroke cases arriving at UK veterinary practices found that only 21.7% of dogs had been actively cooled before being transported, and of those, only around 24% had been cooled using currently recommended methods. Most owners spend the most valuable ten minutes doing the least useful thing: carrying the dog to the car.

The order that works:

1. Get them out of the heat. Shade, airflow or air conditioning.
2. Get them wet. Cold tap water is fine. Soak the whole dog, concentrating on the belly, armpits, inner thighs and paw pads, where blood vessels sit closest to the skin. For a young, healthy dog, cold water immersion is safe and effective. For an older dog, or one with heart or breathing problems, use water that is simply cooler than the dog and rely more on airflow.
3. Add moving air. A fan, the air conditioning, an open car window on the move. Evaporation is what carries heat away. Wet fur with no airflow does very little.
4. Offer water, never force it. An alert dog can drink small amounts of cool water. Give nothing by mouth to a dog that is vomiting or not fully conscious.
5. Stop at around 39°C. The temperature carries on dropping after you stop, and overshooting is its own problem.
6. Go to the vet regardless. Even a dog that looks completely recovered can develop kidney failure and clotting problems over the following 24 to 72 hours.

Three things that make it worse

Cooling slowly with tepid water. This comes from older human first aid thinking, the idea being that cold water constricts blood vessels and traps heat in the core. In dogs, that concern is not supported by substantial evidence. Faster cooling is associated with better outcomes.

Draping a wet towel over the dog. A wet towel left sitting on a dog quickly becomes a layer that holds heat in. Wet towels have been shown to cool far less effectively than immersion, or than soaking combined with moving air. If you are going to use towels, put them under the dog rather than over, and change them constantly.

Driving first and cooling on arrival. Half an hour in Hong Kong traffic is normal. Half an hour of a temperature that is still climbing can be the reason a dog does not make it. The RVC guidance is blunt about this: cool first, transport second.

Which dogs are most at risk?

• Flat-faced breeds: Pugs, French Bulldogs, Pekingese, Boston Terriers, Shih Tzus. Their airway structure makes panting a much poorer cooling system, and they are the recognised highest-risk group.
• Senior dogs, whose temperature regulation and heart and lung function have declined.
• Overweight dogs, where body fat insulates and slows heat loss.
• Thick, double-coated breeds such as Huskies, Chow Chows and Samoyeds, which were not built for a subtropical climate.
• Dogs with existing heart or respiratory disease.

If your dog falls into any of those groups, your margin in summer is much narrower than you think. "He usually copes fine" is not a safe way to judge it.

How do I prevent heatstroke?

Prevention is far easier than the alternative. The ones that matter most in Hong Kong:

• Change the time, not the length. Move summer walks to early morning or after dark. Skip the middle of the day even when it is overcast.
• Test the pavement with the back of your hand. Hold it against the ground for five to seven seconds. If you cannot, neither can their paws. It is a rough test, but a useful one.
• Carry water, even on short walks.
• Sort out airflow in a small flat. If the air conditioning is off, they need a fan and a genuinely cool spot to choose. A closed-up flat can be more dangerous than outdoors.
• Never leave a dog in a car, windows down or not, however quick you think you will be.
• Use cooling wear to help them dump heat. Cool-touch fabric works on the same evaporation principle described above, topping up a cooling system that humidity has already blunted.

Cooling vest

Clay Cooling Vest

Wet it and evaporation pulls heat off your dog while you walk. Sizes M to 3.5XL, so it fits large breeds and flat-faced dogs alike.

From HK$168 See the vest →

Sun hat

Clay Cooling Dog Hat

Keeps direct sun off the top of the head, with a removable air mesh pad and reflective trim. Three colours, sizes S to 2XL.

From HK$108 See the hat →

For smaller dogs and cats there is a cooling bandana from HK$88. The full range sits in Cooling.

Frequently asked questions

Is cold water really safe for a dog with heatstroke?

Yes. The Royal Veterinary College states that the idea that cold water constricts blood vessels and traps heat is not supported by substantial evidence in dogs, and was carried across from older human first aid advice. Cold water immersion is safe and effective for young, healthy dogs. For older dogs or those with heart or lung problems, use water cooler than the dog combined with moving air.

How long does it take to cool a dog down?

There is no fixed number, because it depends on the starting temperature and the method. Work to a temperature rather than a clock: stop at around 39°C, since it keeps falling after you stop. Without a thermometer, cool continuously on the way to the vet rather than waiting.

My dog seems fine after cooling. Do I still need a vet?

Yes. Kidney failure, liver damage and clotting problems triggered by heatstroke can appear 24 to 72 hours later, by which point they are much harder to treat. Get them seen the same day even if they are walking around normally.

Should flat-faced dogs go outside at all in summer?

They should, but on a very different schedule. Flat-faced breeds have airway structures that make panting a much less effective cooling system, and they are the recognised highest-risk group. Walk early morning and after dark, keep it short, carry water, and watch for the early signs. Talk to your vet about your individual dog.

Does cooling wear actually work, or is it just for show?

It works, within its limits, and those limits are prevention. Cool-touch fabric moves heat away by evaporation, the same mechanism a dog uses when panting, which is exactly the system humidity blunts. Once heatstroke signs are present, cool with water and airflow immediately. Clothing will not do that job.

This article is general information and does not replace veterinary diagnosis. If you suspect heatstroke, start cooling and contact your vet.
Sources: Royal Veterinary College VetCompass, "Cool first, transport second"; Cornell University College of Veterinary Medicine, Heatstroke: A medical emergency.