Heat Stress in Dogs and Cats: Spotting It, Stopping It

A healthy adult dog can go from "panting heavily on a walk" to collapse in a very short space of time. Most owners in tropical Asia will never see it themselves — but the ones who do almost always say afterwards that they wish they'd recognised the early signs sooner. This guide is the early signs, and then the emergency protocol, which has changed in the last few years in a way most consumer pet articles have not caught up with.

One thing to fix straight away. The single most common assumption about heatstroke in dogs is that it is a hot-car problem. It is not, or at least not mainly. In UK primary-care veterinary records covering more than 900,000 dogs, exercise was the trigger in roughly three-quarters of heat-related illness events; confinement in a vehicle accounted for around one in twenty. Independent surveillance data reached a very similar split. Hot walks, not hot cars, are where this actually happens — which matters enormously in a city where the walk is available every single day of the year.

A second finding from the same body of research is worth carrying with you as a new arrival. UK dogs developed heat-related illness at surprisingly modest ambient temperatures, with a median around 17°C on event days — a figure researchers attribute largely to lack of heat acclimatisation. Your dog, three weeks off a flight from Britain, is precisely that unacclimatised animal, standing in a climate several categories warmer.

Why dogs and cats overheat differently

Neither species sweats meaningfully. Both have sweat glands only in the paw pads, and their contribution to whole-body cooling is negligible. At ordinary ambient temperatures, dogs shed most of their heat passively — by radiation and convection from the body surface. The catch is that those routes depend on the air being cooler than the dog. As ambient temperature climbs towards body temperature, passive heat loss stops working and evaporation becomes the dominant mechanism available. That is the physiological reason a hot day is not merely "more of" a mild day; it is a different regime.

Evaporation, for a dog, means panting. Panting is more sophisticated than it looks: air is drawn in through the nose, across the moist maxilloturbinates, and out through the mouth, and a dedicated structure called the lateral nasal gland supplies water onto those surfaces for evaporation. The blood draining that region is cooled in the process, which is part of how a panting dog protects its brain. It is an elegant system and it has one obvious dependency — the air has to be able to accept more water vapour.

Which is where humidity comes in. Evaporation depends on the vapour-pressure gradient between wet respiratory surfaces and the surrounding air; as the air approaches saturation, it can absorb less, and panting sheds less heat for the same effort. This is why veterinary heat research uses wet bulb globe temperature — a measure that folds in humidity, radiant heat and air movement — rather than the number on a thermometer. It is also why 32°C at 85% humidity on a Singapore afternoon is not the same animal as 32°C in dry heat.

An honest caveat: the mechanism is well established, but we have deliberately not given you a humidity percentage at which panting "stops working". Dog-specific thresholds of that kind circulate widely online and we could not trace any of them to a primary source. There is also no validated environmental heat index for dogs, whatever the charts on social media suggest. Treat humidity as a serious multiplier, not as a number you can look up.

Cats are usually better at managing heat than dogs, partly because they self-regulate — find the shade, find the tile, stop moving — and partly because they are rarely walked on a lead at one in the afternoon. Dogs do what their owner does, which is the whole problem. Cats also use a cooling route dogs do not: grooming spreads saliva into the coat, where it evaporates. Research published in 2018 found that cats' tongue papillae are hollow and wick saliva deep into the fur, and estimated that saliva evaporation from fur accounts for up to about a third of a cat's evaporative water loss. It is a real mechanism, though it was measured in a very small number of animals.

What cats do not do is pant routinely. Open-mouth breathing in a cat is not the feline equivalent of a dog panting after a run; it is a sign to take seriously, whether the cause is heat, pain, stress or heart and airway disease.

The warning signs, in rough order of severity

Early — slow down, get to shade and water:

• Panting harder than usual for the conditions
• Looking for shade, lying down on cool surfaces
• Excessive drooling
• Bright red gums or tongue

Mid — stop the walk, start cooling, call the vet:

• Refusing to move, dragging behind
• Glassy or unfocused eyes
• Heavy, laboured panting that doesn't slow with rest
• Wobbliness or unsteadiness

Emergency — cool now, then go straight to the vet:

• Vomiting or diarrhoea, particularly if bloody
• Collapse
• Disorientation, seizure, loss of consciousness
• Pale, blue-tinged or very dark gums

Do not treat the first list as background noise because your dog "always pants". The gradient from mild to severe is where the outcome is decided: UK research found survival was very high among dogs with mild heat-related illness and dramatically lower among those who reached severe heatstroke. Meanwhile, the recorded case fatality rate for heat-related illness across UK primary care was around 14%, and around 27% among dogs presenting to emergency practice. This is not a rare, dramatic disease that happens to other people's dogs. It is common, and it kills a meaningful fraction of the animals it reaches.

The emergency protocol: cool first, transport second

Read this section before you need it. This is stabilise-and-transport guidance, not treat-at-home guidance. Nothing here replaces a vet, and a dog that has had heatstroke needs veterinary assessment even if it looks fine once cooled.

The guiding principle used in veterinary emergency medicine is cool first, transport second. Cooling begins where the animal is, and continues on the way, rather than waiting until you arrive at a clinic. The reasoning is straightforward: how far the body temperature rises and how long it stays there drive the damage, and delay to treatment is a documented risk factor for death — one referral study found dogs whose admission was delayed beyond 90 minutes had roughly twice the relative risk of dying.

What to do:

1. Stop everything and get the animal out of the heat. Shade, indoors, air conditioning, in front of a fan — whatever is nearest.
2. Get water onto the dog, and keep getting water onto the dog. Use whatever water you have, as long as it is cooler than the animal. Pour it over the body rather than dabbing it on. Do not spend time looking for water of an ideal temperature.
3. Get air moving over the wet coat. A fan, an open car window on the way, air conditioning on full. Water without airflow is doing half the job.
4. Ring the vet while this is happening so they are ready, and go.
5. Offer water to drink but do not force it, and do not pour water into the mouth of a collapsed or semi-conscious animal.

The cold water question, honestly. You will find plenty of pet websites — some of them recent — saying never to use cold or iced water, on the theory that it causes surface blood vessels to constrict and traps heat in the core. Veterinary researchers who study canine heatstroke now describe that advice as unsupported by the evidence, and note that it appears to trace back to a single experimental study from 1980. Worse, it has been documented to cause real harm by delaying cooling while owners search for warmer water. Current emergency guidance describes cold water immersion as appropriate for young, healthy dogs, and pouring water combined with air movement as the preferred approach for older dogs or dogs with existing health problems. The practical instruction from the researchers themselves is simple: use whatever water is available, provided it is cooler than the dog.

Two caveats that are not contested. If you immerse a dog, its head must be supported and kept clear of the water — aspiration is a genuine risk, particularly in flat-faced breeds and in any animal that is not fully conscious. And immersion is not a substitute for going to the vet; it is what you do on the way.

What not to do:

• Do not wrap or cover the dog in wet towels. This is the most commonly used method and one of the least effective — a towel laid over the body can trap heat rather than release it. If you have towels, use them to carry water, not as a blanket.
• Do not rely on ice packs. They perform poorly as a whole-body cooling method compared with water plus airflow.
• Do not put alcohol on the paw pads. It has fallen out of favour on grounds of toxicity, tissue damage and simple ineffectiveness.
• Do not keep cooling indefinitely. Overshoot into hypothermia is a real complication; veterinary sources generally stop active cooling in the region of 39.4°C. If you are not measuring temperature — and most owners are not — this is another reason the animal needs to be with a vet quickly rather than in your bathroom for an hour.

And then go, even if it looks better. Heatstroke causes injury that unfolds over the following day or two: acute kidney injury, disseminated intravascular coagulation, gastrointestinal damage that presents as bloody diarrhoea, neurological signs, and cardiac arrhythmias. Veterinary sources emphasise monitoring across at least the first 24 hours precisely because complications have a delayed onset. An animal that perked up in the car is not a resolved case.

That management is not cheap. A severe heatstroke case in Singapore or Hong Kong means intravenous fluids, bloodwork, clotting checks and usually a night or more in hospital — nights that are quoted in the hundreds, and considerably more in intensive care. It is exactly the kind of bill that makes people wish they'd sorted insurance out on a quiet afternoon rather than in a waiting room. If you haven't looked at it yet, our guide to pet insurance in tropical Asia covers how cover works here, with city-specific write-ups for Singapore and Hong Kong — and it's honest about the pets for which it isn't worth buying.

Breeds and individuals at higher risk

The intuitive list — pugs, bulldogs, French bulldogs, Persians, Himalayans — is real but incomplete, and the research is more interesting than the folklore.

In a large UK primary-care study, brachycephalic dogs had roughly twice the odds of heat-related illness compared with mesocephalic dogs. But bodyweight above 50kg carried a larger effect than skull shape did, and other elevated-risk breeds included the Chow Chow (by a wide margin, though on a small sample), the Greyhound and the Golden Retriever — a thick-coated dog, a lean sighthound and a perfectly ordinary family dog, none of them flat-faced. Being twelve or older, being heavier than average for the breed, and being purebred rather than crossbred all raised the odds too. In a separate analysis, obesity was associated with roughly double the risk of dying once heatstroke occurred.

Brachycephaly also mattered more in some scenarios than others: its effect was largest for environmental and vehicular heat exposure and smallest for exertional cases. Put crudely, a flat face is worst when the animal cannot escape the heat.

The honest summary is that heatstroke is multifactorial. Flat faces, thick coats, large body mass, excess weight, age at either extreme, and existing heart or airway disease all stack, and a dog with none of them can still get into trouble on the wrong afternoon.

If you have one of these animals, the rule isn't "be careful in summer." There is no winter here. The rule is: you have a year-round consideration, and your daily routines should reflect it.

Older dogs are worth singling out, because heat stress and joint pain look identical from the other end of the lead. Both show up as a dog that slows, stops, or refuses to go further. If yours is doing that and you can't tell which it is, start with the time of day — then read our guide on joint supplements and what the evidence supports, which covers how to separate the two before you spend anything.

Prevention in an air-conditioned expat life

The version of this problem that catches expats is specific. You live in an air-conditioned flat, you work in an air-conditioned office, and your dog spends twenty-two hours a day at 24°C. That is not acclimatisation — it is the opposite. An animal that lives permanently in cooled air is arguably less prepared for the two hours it spends outside than one that experiences a gentler gradient, and the transition from a cold lift lobby to a 33°C pavement is abrupt in a way it never was in London.

None of which is an argument for switching the air conditioning off. It is an argument for taking the outdoor two hours seriously.

• Walk early and late. Before around 8am and after around 7pm through the hottest stretches. This is the single highest-value change, because exertion is the dominant trigger.
• Pavement check. If you can't hold the back of your hand on it for five seconds, it's too hot for paws — and the radiant heat coming off it is going into the dog too.
• Shorten and flatten the route on bad days. Substitute sniffing and shade for distance. A dog does not need a fixed daily mileage; it needs stimulation.
• Fresh water everywhere — at home, in the bag, in the car.
• Never leave a pet in a parked car. Not for "two minutes", not with the windows cracked. It is the minority cause of heatstroke but it remains an entirely avoidable one.
• Watch the enclosed spaces you don't think of as hot. A car park lift lobby with no air conditioning, a stairwell, a store room, a balcony that gets afternoon sun, a bathroom with the door shut. The recorded feline cases are overwhelmingly this kind of confinement, including at least one published series involving tumble dryers.
• Balconies and rooftops. A shaded balcony at 9am is a sun trap at 2pm, and a cat that went out there voluntarily may not be able to get back in.
• Air conditioning when you're out, for indoor pets that aren't acclimatised — particularly cats and small dogs.

None of these are exotic. All of them are the difference between a pet that lives well in this climate and one that has a near-miss every wet season. If you have only just arrived, our guide to the first thirty days sets out how the acclimatisation period should actually be paced, and the wider picture of what changes for a temperate-climate animal is in our primer on pet health in tropical Asia.

If your move is to or from the Gulf rather than South-East Asia, the same physiology applies in a drier heat — a Dubai summer is every bit as dangerous for a temperate-climate dog, and the drier air changes the arithmetic of evaporation without removing the risk. The import paperwork is a different beast entirely, though, and DubaiExpat covers it properly in their guide to moving a pet from the UK to Dubai.