Every summer, well-meaning owners pop into a shop 'just for a minute' and leave their dog in the car with a window cracked. It feels harmless. It very often isn't. Dogs can suffer fatal heatstroke in cars far faster than most people expect, and by the time it's obvious something is wrong, it can be too late to act.
This guide covers the numbers behind why cars are such effective ovens, why the usual precautions don't work, how to spot heatstroke, and — because this is the question people actually need answered in the moment — what to do, step by step, if you see a dog in a hot car right now.
How fast does a car actually heat up?
On a day that feels like a pleasant 22°C outside, the inside of a parked car can reach around 47°C in under an hour, and much of that rise happens in the first ten to twenty minutes. Glass lets sunlight in freely but traps the heat that bounces back off the seats and dashboard, so the temperature climbs steadily even with no direct sun on the car itself.
You can check what a given outside temperature does to the inside of a vehicle using our /hot-car-dog-temperature calculator. It's a genuinely sobering exercise — plug in a normal spring or summer day and watch how quickly 'warm' becomes 'dangerous'.
Why cracked windows and shade don't make it safe
A window left an inch or two open makes almost no measurable difference to how hot a car gets. It allows a tiny amount of air exchange but does nothing to stop the greenhouse effect building up inside. The same goes for parking 'in the shade' — the sun moves, shade disappears, and a car that was shaded when you parked can be in full sun twenty minutes later.
There is no safe amount of time to leave a dog alone in a car in warm weather, including weather that doesn't feel hot to a person standing outside. The only reliable way to keep a dog safe is not to leave them in the car at all.
Signs of heatstroke in dogs
Heatstroke can develop quickly and escalate from mild distress to a genuine emergency within minutes. Flat-faced breeds (French Bulldogs, Pugs, Bulldogs and similar), older dogs, overweight dogs, and those with thick coats or existing heart or airway problems are at much higher risk, but any dog can be affected.
- Heavy, rapid panting that doesn't settle
- Drooling more than usual, or thick, ropey saliva
- Bright red or very pale gums
- Wobbliness, disorientation or collapse
- Vomiting or diarrhoea
- Seizures, in severe cases
What to do if you see a dog in a hot car
This is the part people most want a clear answer to, so here it is, in order.
- Call 999 and ask for the police. In an emergency involving an animal in immediate danger, the police — not the RSPCA — have the power to act quickly, including forcing entry if necessary. The RSPCA has no legal power of entry to a vehicle and cannot break in themselves.
- Also call the RSPCA on 0300 1234 999 to log the incident and get advice, especially if the situation isn't immediately life-threatening. In Scotland contact the Scottish SPCA, and in Northern Ireland the USPCA.
- Note the car's registration, make, model and colour, and the time you found the dog.
- If you're near shops, ask staff to make a tannoy announcement asking the owner to return to their vehicle urgently.
- Stay with the dog if you safely can, and keep monitoring how they're doing while help is on the way.
- Take photos or video of the dog and the situation, and get contact details from any witnesses — this matters if the incident is investigated later.
- Only consider breaking a window as an absolute last resort, if the dog is showing severe signs of heatstroke or collapse and there is no other way to help in time. Doing so could technically be treated as criminal damage, so speak to the police first if you possibly can, and be prepared to explain and show evidence of why you acted.
Cooling first aid while help arrives
If you're able to get to the dog, move them into shade or a cooler space straight away. Offer small amounts of cool (not ice-cold) water to drink if they're conscious and able to swallow normally. Pour or sponge cool water over their body, particularly the belly, armpits and paws, and use air movement — a fan, or simply the car's air conditioning — to help evaporation along.
Avoid ice or very cold water, which can constrict blood vessels near the skin and actually slow heat loss from the body's core. The aim is steady cooling, not shock cooling. Get the dog to a vet as quickly as possible even if they seem to be recovering — heatstroke can cause damage that isn't obvious straight away, including to the kidneys, liver and blood clotting.
The law in the UK
Leaving an animal in a situation likely to cause suffering is an offence under the Animal Welfare Act 2006 in England and Wales, and under equivalent legislation in Scotland and Northern Ireland. Owners can face fines, disqualification from keeping animals, or prosecution if a dog suffers or dies as a result of being left in a hot car.
You can find printable awareness posters for your car window, workplace or local shop using our /hot-car-poster resource — a small, practical way to remind other dog owners of the risks before they get in the car.
Prevention is simpler than rescue
The easiest fix is also the most obvious one: if you can't take your dog into wherever you're going, leave them at home. Plan dog-friendly stops on hot days, keep water and a shade option in the car for genuine emergencies like breakdowns, and build in the habit of asking 'where does my dog go?' before every short errand, not just long journeys.
When to speak to your vet
Any dog who has been in a hot car and shown signs of distress, even briefly, should be checked over by a vet, ideally the same day. Heatstroke can cause internal problems that only show up hours later, and early treatment makes a real difference to outcome. If you're ever unsure whether a dog's symptoms need urgent attention, it's always safest to call your vet straight away rather than wait and see.