Dog heat stress: early signs and the cool-down that works

Quick answer

Most dogs that develop heatstroke were not shut in a car. They were out being walked or played with by an owner who did not think it was that hot. Veterinary studies of dogs presented with heat-related illness have consistently found exercise, not confinement, to be the most common trigger.

A dog cools itself almost entirely by evaporating water from its airway. That is a narrow margin at the best of times, and it disappears in humid air, in a flat-faced dog, in a heavy coat, and in a dog carrying extra weight. The early signs appear well before collapse, and recognising them is the whole game.

Comfortable panting is quiet, rhythmic and stops when the dog rests. Panting that gets louder and does not settle is the first warning.

• Heat illness is a spectrum. Heat stress, then heat exhaustion, then heatstroke, and it can move through all three in minutes.
• Cool the dog first, then travel. Cooling on the way is better than cooling on arrival.
• Pour cool water over the dog continuously and get air moving. Do not drape wet towels and leave them on.
• Brick-red gums, thick ropey drool, wobbliness or vomiting mean stop everything and start cooling now.
• Any dog that has had a heat episode needs veterinary assessment even if it looks recovered, because the serious damage declares itself over the following days.

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Never leave a dog in a parked car, a conservatory, a caravan, a greenhouse, a horsebox or a crate in the sun, not even briefly and not with the windows cracked.

A closed vehicle in sunshine behaves as a solar collector. The interior air temperature climbs steeply within minutes and keeps climbing, and a cracked window makes almost no difference to the rate. A dog in that space has no way to cool itself because the air it is panting into is already hotter than its own body, so evaporation stops working. This is one of the few situations where the animal has no escape route at all.
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Decide in 60 seconds

How a dog actually loses heat

A dog generates heat constantly, and in warm conditions it has only a few routes to shed it.

Radiation and convection from the body surface work only while the surroundings are cooler than the dog. On a hot day they stop working, and on a very hot day they run backwards and the dog gains heat from its environment.

That leaves evaporation, and dogs evaporate from the respiratory tract. Air is drawn in through the nose over moist turbinates, water evaporates and carries heat away, and the air leaves through the mouth. This is why an overheating dog pants with an open mouth and a wide, long, flat tongue: it is maximising the wet surface area the air passes over.

Two things break this system.

The first is humidity. Evaporation is driven by the difference between the water content of the airway surface and the water content of the air. In humid air that gradient is small, so the same panting effort removes far less heat. This is why owners are caught out on muggy days that do not feel extreme.

The second is airway obstruction. Panting is work, and work makes heat. A dog that has to fight to move air is generating extra heat in order to lose heat, and if the airway is narrow enough that trade goes negative. This is the core problem for flat-faced breeds and for any dog with laryngeal paralysis.

Paw pads sweat a little, which is why a dog on cool tiles or wet grass benefits, but the contribution is small and cannot be relied on.

Which dogs are already behind before they start

Flat-faced breeds.

French bulldogs, English bulldogs, pugs, boxers, Boston terriers, shih tzus, Pekingese and their crosses have the same amount of soft tissue as a longer-nosed dog packed into a shorter skull. Narrow nostrils, a long soft palate and a narrowed windpipe all restrict airflow, and the effort of panting causes swelling that restricts it further. Some of these dogs are in trouble on a day their owners describe as pleasant.

Overweight dogs.

Fat is an insulator and it adds mechanical load to the chest and abdomen, so the same walk costs more heat production and the heat escapes more slowly. Weight is the single most modifiable risk factor here.

Thick double coats.

Huskies, malamutes, chows, Newfoundlands, German shepherds and Bernese mountain dogs carry an insulating undercoat that does its job in both directions. A blown, matted or ungroomed undercoat is worse than a well-maintained one because it traps a still layer of hot air against the skin.

Large and giant breeds.

Heat is produced in proportion to body mass and lost in proportion to surface area. Bigger dogs have less surface per kilogram, so they heat up faster and cool down slower.

Dogs with laryngeal paralysis.

Classically older Labradors and other large breeds. The laryngeal cartilages fail to open properly, so the dog cannot move enough air, and the first presentation is often a heat crisis on a warm walk. The tell is a change in the bark and a harsh raspy noise on breathing in.

Dogs with heart or respiratory disease, puppies, and seniors.

All have less reserve. Puppies also have poor judgement about when to stop.

Any dog that has had heatstroke before.

Previous episodes are a recognised risk factor for another one.

Dogs that have just travelled somewhere hotter.

Acclimatisation is a real physiological process that takes weeks. A dog flown or driven from a cool climate into a hot one has none of it.

The stages, in the order they appear

Heat stress.

The dog pants harder and more constantly than the activity warrants. It seeks shade, lies on tiles or in wet grass, drinks more, slows down, or starts lagging behind on the lead. Some dogs become restless and unsettled instead of slowing. This stage is entirely reversible and it is where you want to be acting.

Heat exhaustion.

Panting is now loud and laboured, and it does not stop when the dog rests. The tongue is wide, long and flat, sometimes hanging further out than you have seen before. Saliva becomes thick and ropey rather than watery. Gums turn a bright brick red as blood is shunted to the skin. The heart rate is fast, the dog looks glazed, and coordination starts to go. Vomiting and diarrhoea often appear at this point, and there may be blood in either.

Heatstroke.

Staggering, weakness in the hindquarters, collapse, tremors, seizures, and loss of consciousness. Gums that were brick red change to pale, grey, blue or muddy as circulation fails. Pinpoint bruising may appear in the gums, the belly or the inside of the ears, which reflects a clotting failure. At this stage the dog is in multi-organ trouble and every minute of delay costs.

A dog can move from the first stage to the last in a very short time, and a dog can also be found already in the last stage without anyone having seen the first two.

Cool first, then travel

This is the most important practical change in heatstroke advice, and it is the opposite of what many owners instinctively do.

The damage in heatstroke is done by the length of time the body spends above its tolerable temperature. Every minute spent driving with an uncooled dog on the back seat is a minute of continuing injury. Start cooling where you are, keep cooling in the car, and let the veterinary team continue it on arrival.

Use cool water, continuously, and move air over the dog.

Running cool tap water over the whole dog, or immersing the body in cool water while keeping the head clear, both work. Hosing is fine. The important part is that the water keeps flowing and taking heat with it, and that air is moving over the wet coat. A garden hose plus a breeze beats a bucket poured once.

The old advice to use only tepid water, on the theory that cold water causes the skin vessels to clamp shut and trap heat, has not held up for dogs. Cool water applied continuously cools faster and is what current veterinary emergency guidance supports.

Do not drape wet towels and leave them on the dog.

This is the single commonest cooling mistake. A wet towel left in place quickly reaches the dog's own temperature and then behaves as an insulating blanket that stops airflow reaching the coat. If you use towels, keep replacing them with freshly cooled ones every couple of minutes, or better, pour water over the dog and leave the coat wet and exposed to moving air.

Get the dog off hot ground.

Into shade, onto cool tiles, onto wet grass, or into the footwell of an air-conditioned car. Tarmac and paving radiate heat upward for hours after the sun has moved.

Offer water, do not force it.

A conscious dog that wants to drink should be allowed to drink cool water freely. Never pour water into the mouth of a dog that is collapsed, semi-conscious or vomiting, because it goes into the lungs.

Know when to ease off.

Vets stop active cooling before the temperature reaches normal, because a cooled body keeps losing heat for a while afterwards and overshooting into hypothermia causes its own problems. You will not have a thermometer reading in most cases, so the practical rule is to cool hard while the dog is clearly overheated, ease off as it improves, and tell the veterinary team exactly when you started and stopped.

Call ahead while you cool.

Someone else phones the practice, describes the situation and asks them to prepare. Do not stop cooling to make the call.

Water available at both ends of the walk, and an honest look at body weight, prevent more heat emergencies than any gadget.

What else looks like this

Fever.

An infected dog has a raised temperature too, but the mechanism is opposite: the body has deliberately moved its target upward. A feverish dog is usually dull, off food and often shivering rather than seeking cool surfaces, and there is no heat exposure or exertion in the history. This matters because human fever medicines are wrong for both situations in dogs and dangerous in their own right.

Airway obstruction crisis.

A flat-faced dog or a dog with laryngeal paralysis can go into respiratory distress from excitement alone. There is loud upper-airway noise, and the dog may go blue rather than brick red. Heat and obstruction usually occur together, and both are treated as emergencies.

Heart failure.

Coughing, exercise intolerance and laboured breathing that has been building over weeks, with the collapse happening at low effort. Gums are pale or blue rather than brick red.

Pain or anxiety.

Both cause panting without heat. The context tells you: a panting dog in an air-conditioned room after a car journey is anxious, not overheated. Pain-related panting usually comes with a reluctance to move a particular part.

Poisoning and metabolic emergencies.

Some toxins and some metabolic conditions raise body temperature and cause tremors, and they can look identical from the outside. This is one of several reasons a dog that has had a heat episode should be seen rather than simply watched.

The days afterwards

A dog can look normal within an hour of a bad episode and still be seriously ill.

Heat injures the lining of the gut, the kidneys, the liver, the clotting system and the brain, and those injuries declare themselves over the following one to three days. Bloody diarrhoea, reduced or absent urination, jaundice, bruising, ongoing dullness, disorientation or difficulty breathing after an episode are all reasons to go back immediately.

This is why the veterinary answer to "he seems fine now" is still to bring the dog in. Blood tests and monitoring during that window are what catch the acute kidney injury and the clotting failure while they are still treatable.

What never to do

Do not give paracetamol, ibuprofen, aspirin or any other human medicine. They do not lower temperature in heatstroke because the problem is not a raised set point, and they cause serious poisoning in dogs.

Do not shave a double-coated breed to keep it cool. The undercoat insulates against incoming heat as well as outgoing, and shaving exposes skin to sunburn and can permanently damage regrowth. Brush the undercoat out instead so air can move through it. Clipping a matted coat is a separate matter and does help.

Do not use a tight-fitting muzzle on a warm day. A muzzle that holds the mouth closed prevents panting. Only a basket muzzle that allows the mouth to open fully and the tongue to extend is acceptable in warm weather.

Do not put a dry cooling coat on a dog. These work by evaporation and must be soaked and re-soaked, and a dry one is simply an extra layer of insulation.

Do not exercise to a schedule. The walk that was fine last week is not automatically fine today.

Do not assume shade is enough for a tethered or crated dog. Shade moves, and a crate in a garden becomes a solar oven when the sun swings round.

Do not rely on a fan alone for a dog that is already in trouble. Moving hot air over a dry coat does very little. Wet the dog first.

Do not delay cooling in order to get to the vet faster.

When to get help

Go immediately, cooling as you go, for collapse, staggering, seizures, unresponsiveness, vomiting or diarrhoea during or after heat exposure, blood in vomit or stool, or gums that are brick red, pale, grey or bruised.

Go the same day for any dog that has been noticeably overheated, even one that appears to have recovered, and for any flat-faced dog that had a breathing crisis in the heat.

Book an assessment before summer for any dog with a flat face, a changed or hoarse bark, noisy breathing, exercise intolerance, or a previous heat episode. Those are the dogs whose next hot day is the risky one, and much of that risk can be reduced in advance.

Bring the timeline: what the dog was doing, for how long, the temperature and humidity, when the first sign appeared, when you started cooling, what you used and for how long, whether there was vomiting or diarrhoea and whether it contained blood, whether the dog has urinated since, and any medication given. A short video of the breathing before you left is genuinely useful.

Recovery means an alert dog, drinking normally, urinating normally, with a settled breathing pattern and no blood in the stool.