Our bodies have one real way of cooling down in the heat, and it's sweat. Not the sweat sitting on the skin, but the evaporation of it. As sweat lifts off, it carries heat away with it. The UK Health Security Agency puts it plainly: once the air around you is warmer than your skin, sweating is more or less the only tool your body has left.

Now take that tool away. When the air is already thick with moisture, the sweat has nowhere to go. It just sits there instead of evaporating. Your baby is still sweating, still losing fluid, but getting almost none of the cooling in return. That is why a muggy 24°C can be harder on a small body than a dry 30°C, and it's exactly the sort of day that catches us all out.

There's a reason forecasters talk about how hot it "feels" rather than the bare temperature. The measure that safety bodies, the military and sports scientists actually use to judge heat risk is called wet bulb globe temperature, and it weights the three ingredients very unevenly on purpose.

One example shows how much difference the moisture makes. At around twenty per cent humidity, conditions don't tip into genuinely dangerous until roughly 40°C. Push the humidity up to eighty per cent and that danger point drops to about 31°C. Same sun, same little body, nine degrees of difference, and the only thing that changed was how much water was in the air.

Babies get into trouble faster than adults, and it isn't because they're delicate. They're small, so they carry a lot of surface area for their size and they gain heat quickly. During sleep their temperature control quietens down. And then the big one: they can't do a single thing about it. They can't push off a cover, shuffle into the shade, ask for a drink or tell you they feel dreadful. They rely completely on us to notice for them.

They can't tell you, so it helps to know what you're actually looking for.

Any one of these on its own isn't a crisis, but together they're a clear cue to cool your baby down and get somewhere cooler.

The old rule about dressing a baby in one more layer than you're wearing quietly falls apart in humidity. On those days it's about moisture and moving air, not warmth. Light, loose clothing in cotton rather than synthetics. A fan is genuinely useful, but for keeping the air in the room moving, not pointed straight at your baby, and do bear in mind that once the air itself is warmer than they are, a fan is only shifting hot air about. Offer feeds more often too. Breastfed babies especially will want them, and that's precisely as it should be.

This is the part where I'm meant to tell you a good sun shade solves all of the above. It doesn't, and I'd rather be straight with you.

What direct sun does add is a genuine radiant heat load on top of everything else, separate from the air temperature, plus the UV itself, which a baby's skin has no business being exposed to. That part a proper shade really does handle. SnoozeShade blocks up to 99 per cent of the sun's UV, and it's made from an air-permeable mesh, so unlike a blanket it doesn't trap air. On the sun side of the problem, it does its job well.

What it cannot do, what nothing draped over a pram can do, is cool air that's already too hot. It isn't air conditioning and I've never pretended it is. On a dangerously hot, humid day the honest answer isn't a clever bit of kit. It's the cooler hours of the morning or the evening, or simply staying in. A shade protects your baby from the sun. It doesn't turn a hot day into a safe one, and none of us should let it talk us into false confidence.

Years before I made the first SnoozeShade, my daughter had a febrile convulsion. Anyone who has watched their child have one knows the particular fear it leaves behind, the way you never quite stop watching for them getting too hot. So the days that worry me most aren't the bright, dry, obviously hot ones. Everyone's careful on those. It's the grey, sticky, twenty-four-degree afternoon that doesn't look like anything much at all. Check the humidity, not just the temperature. And on the day your baby's body is telling you one thing while your phone insists on another, believe your baby.