Everyone watches the thermometer in summer. Fewer people watch the humidity, and that's the gap where dogs get caught out. A dog can overheat on a day that doesn't even feel that hot to you, simply because the air's too wet for their cooling system to work properly.
Here's what's going on, who needs the closest eye kept on them, and what actually helps.
Panting is the whole system, not a backup plan
Dogs don't sweat the way we do. Panting is their main way of shedding heat — moving air over a wet tongue and airway so moisture evaporates and takes warmth with it. It's an efficient system on a dry day.
On a humid day, it isn't. The air's already carrying a lot of moisture, so there's less room for more to evaporate off your dog. The panting looks the same from the outside. Underneath, it's doing a fraction of the work.
Who needs watching closest
Some dogs run into trouble faster than others. According to the RSPCA, the dogs most at risk of overheating are:
- Dogs with existing health conditions — unfit or overweight dogs, and those with heart or respiratory disease, heat up faster and take longer to cool down
- Flat-faced (brachycephalic) breeds — a VetCompass study by Nottingham Trent University and the Royal Veterinary College found breeds like bulldogs, French bulldogs and pugs are at higher risk of heatstroke, because their shorter snouts make panting far less effective
- Thick-coated dogs — losing heat through the body is harder with a heavy coat, or when they're dressed in doggy clothes
Worth knowing: the RSPCA also flags that these dogs can struggle even in relatively mild spring weather, especially straight after a cold winter, before anyone's coat or fitness has adjusted to warmer conditions.
The signs to watch for
The RSPCA lists these as the key warning signs of a dog overheating:
- Heavy panting and difficulty breathing
- Excessive drooling
- Lethargic, drowsy, or uncoordinated movement
- Collapse or vomiting
If you see any of this, don't wait to see if it passes. Get your dog into shade, offer water, and start cooling them down.
What actually helps
On the walk itself. Blue Cross recommends walking at cooler times of day and checking the ground temperature with the back of your hand before setting off — if it's too hot for you, it's too hot for their paws. Worth noting their advice for evening walks too: humidity often climbs after dark, so a cooler-feeling evening isn't automatically a safer one.
Rest and shade. Blue Cross suggests limiting exercise altogether above 20°C, and being even more cautious with overweight or flat-faced dogs, who can struggle at lower temperatures than that.
Cooling tools. Paddling pools, damp towels underneath (never draped over the body — the RSPCA is clear this can trap heat rather than release it), frozen treats, and water-activated cooling coats all help. The coats work on the same evaporation principle as panting, which is exactly why they stop being as effective in properly humid conditions too.
If it goes further. The RSPCA's advice is "cool first, transport second." Get your dog out of the heat, pour cool (not icy) water over their neck, stomach and thighs — avoiding their head — and fan them, before heading to the vet with the windows down or the air-con on.
The takeaway
Heat gets the headlines, but it's the muggy days that catch dogs out, because the one tool they have for cooling down works so much less well when the air's already saturated. Keep a closer eye on flat-faced, overweight, older and thick-coated dogs in particular, and don't wait for obvious signs before offering shade, water and rest.
Topping up fluids matters here too — a dog working harder to cool down is losing water faster, often before you'd notice. That's the gap Better Hydration is built to close: a quick top-up on the days their cooling system is under the most strain.
If your dog shows signs of heatstroke, this is an emergency — cool them down and get to a vet straight away. This is general guidance, not a diagnosis.
Sources: RSPCA – Heatstroke in dogs · RSPCA – Dogs die on hot walks · RVC VetCompass – flat-faced breeds and heatstroke risk · Blue Cross – Top tips for keeping your dog cool in summer