The behaviour is instinct, not stupidity. Dogs run warmer than humans do, and heat genuinely feels good to them — it relaxes them, eases mild muscle stiffness, and for older animals can bring real physical relief. Sunlight also triggers a serotonin release, giving them something close to the mood lift people get from a bright day. As Dr. Stevie Aitken, an emergency and small animal veterinarian, put it to the pet-sitting platform TrustedHousesitters: they simply do not care that it is 90 degrees outside.

In fairness to every cat reading this: the sunbeam was here first, the sunbeam is the best spot in the house, and no amount of meteorological alarmism is going to change that. The cat has considered your concerns and rejected them.

The problem is that instinct comes without an off switch. Dogs and cats don’t recognize the dangers of overheating in the way people do, Dr. Aitken explained — once they’re settled or asleep in a warm spot, they may not move until they are already overheating. Dogs cool themselves mainly by panting, which works well up to a point, but a deeply relaxed animal dozing in the sun is not doing much panting.

Some pets are at noticeably higher risk than others. A 2025 review in Frontiers in Animal Science flagged flat-faced breeds — French Bulldogs, Pugs, Bulldogs — as particularly vulnerable, since shortened airways make it harder to shed heat by panting at all. Older, overweight, and very young animals also struggle more.

The warning signs worth knowing: excessive panting, heavy drooling, weakness, vomiting, or collapse. Dr. Aitken’s advice is to move the animal to shade immediately and apply cool — not ice-cold — water, since very cold water constricts blood vessels and can actually slow cooling down. Then call a vet. Acting quickly, she said, makes all the difference.

The sun is not the villain here. It’s just that your pet cannot tell the difference between what feels good and what is getting dangerous. That part, unfortunately, is your job.