The thing nearly every heat campaign gets wrong
Ask anyone what causes heatstroke in dogs and they will say a parked car. The Royal Veterinary College went through the records of dogs presenting to primary care practices and found that 74.2% of cases were exertional — caused by exercise. Cars were a small minority.
Worse, it does not take a heatwave. In that UK data the average case happened at a wet bulb globe temperature of 16.5°C, which is about 62°F. Not a red-alert day. A pleasant one, with a dog running.
So the useful question is not "is it hot out". It is "what am I about to ask this particular dog to do". That is what this page weighs.
Why the dog matters more than the weather
A flat face is not a cosmetic difference. Compared with dogs of ordinary muzzle length, the RVC found brachycephalic dogs at:
| All flat-faced | Bulldog | French bulldog | |
|---|---|---|---|
| Heatstroke from exercise | 1.3× | 3.7× | 3.0× |
| From hot weather | 2.4× | 7.5× | 3.2× |
| In a vehicle | 3.1× | 16.6× | 6.7× |
The breed columns are against a labrador. A bulldog in a car is not slightly worse off than a labrador in a car — it is sixteen times more likely to end up at a vet with heatstroke.
The mechanism is simple. Dogs shed heat by panting, which is evaporation happening across the surfaces of the airway. Shorten the airway and squash it, and you have removed most of the radiator. Add a thick coat, extra weight, or a heart or airway condition and you take away more of it.
Why humidity hurts them more than it hurts you
You sweat over your whole body. A dog evaporates from its airway and a little from its paws. Both systems fail as the air gets wetter, because evaporation slows when the air is already carrying water — but the dog has far less spare capacity to lose. 85°F at 30% humidity and 85°F at 80% are different days for you and very different days for a dog.
The feels-like number on this page is the US National Weather Service heat index, which was built for people. It is the best-validated way to combine heat and humidity that exists, and it understates the problem for dogs. Read it as a floor.
The pavement chart everyone shares
You have seen it: 77°F air means 125°F asphalt, 87°F air means 143°F. Those figures get quoted everywhere, and they are worth a second look. A one-degree rise in air temperature, from 86 to 87, is shown moving the asphalt eight degrees. Surfaces do not behave like that. What actually drives surface temperature is how long the sun has been on it, what it is made of, and what color it is — not the air reading.
Which is why the practical test beats the chart. Washington State University's teaching hospital puts it like this: press the back of your hand flat on the pavement and hold it for seven seconds. If you have to lift it, do not walk your dog on it.
Evening walks feel like the safe option and often are not. Asphalt has been absorbing sun all day and gives it back for hours after sunset. Early morning is the genuinely cool window.
What it looks like when it is going wrong
- Panting that has turned loud, frantic and open-mouthed rather than steady, and does not settle when they stop.
- A tongue that is very wide, very red, or hanging further than usual.
- Drooling much more than normal, or thick ropey saliva.
- Wobbling, stumbling, sitting down and refusing to move — the point at which this is an emergency.
- Vomiting or diarrhea on a hot walk.
- Gums that are brick red, or gray or blue.
If you are seeing the bottom half of that list, stop reading and go to what to do about heatstroke. Cooling comes before driving, and the method most websites still recommend is the wrong one.
Taking a dog somewhere hot
The dog that lives in it copes better than the dog that arrives into it. Acclimatisation is real and it takes days to weeks, so the first few days of a trip south are the risky ones, not the middle.
- Plan the first three days as if the dog were unfit, because for that climate it is.
- Walks at first light. Not evening — see the pavement section.
- Book accommodation with air conditioning, and check it works before the dog is in the room.
- Carry more water than you think and a bowl they will actually drink from.
- Find the nearest emergency vet on the first day and put it in your phone. Doing that at 2pm on day four while a dog is collapsing is not the moment.
- If the dog is flat-faced, take the table above seriously when choosing where to go at all.