Why chilli and tea can cool you down on a hot day
On hot days, ice-cream and beer are out — and chilli and tea are in.
It sounds like a Jerry Seinfeld bit from the ‘90s: “Did you ever notice that people from hot countries have the hottest food and drinks? They’re already hot — do they want to get hotter? What’s the deal with that?!”
On the face of it, downing hot food and drinks in hot weather does sound like something that would confound and delight a stand-up comedian.
But it can actually be a lot better at cooling you than cold food and drinks.
Sweat, baby, sweat
“Sweaty wreck” is not a fun state to be in, but your body is actually doing you a favour (as hard as that is to believe when there’s a steady trickle into your butt crack) by trying to cool itself down.
Optimum human body temperature is about 37 degrees Celsius. Obviously, the external temperatures vary wildly from that number, so our bodies have a range of tricks to keep themselves within their preferred zone.
A minor cooling mechanism prompts tiny muscles under your skin to pull your hairs flat to stop them trapping heat. But the major cooling mechanism is, of course, sweat — us humans are one of the few animals who sweat through our skin, an adaptation we probably developed to become ruthlessly efficient persistence hunters.
When your nervous system senses rising temperatures, it triggers a type of sweat gland called eccrine glands to release the salty stuff. There are sweat glands pretty much all over your body (a second type of sweat gland, apocrine glands, is responsible for the sweat that causes BO) and you have somewhere between 2 to 4 million of them.
Even though it doesn’t feel like it, you sweat all the time —you just might not notice because the sweat evaporates right away, or because it’s reabsorbed back into your body. If you live in a hot climate, your body can sweat up to two to three litres per hour (turning that butt crack trickle into a torrent).
Sweat cools you by evaporating from your skin and taking heat away with it. The humidity of the air is a crucial factor here: humid air is already saturated with moisture, and is worse at carrying sweat from your skin. That’s why you always overhear people in elevators awkwardly small-talking about how they prefer dry, higher heat to humid, lower heat.
What you eat makes you sweat
Heat isn’t your body’s only sweat trigger: anxiety or stress can make you sweat even when it’s freezing, while hot and spicy foods can bring on what’s known as gustatory sweating.
So why do hot foods have this reaction even though they’re not literally hot? It’s because the chemical ingredients that make foods spicy (notably one compound called capsaicin) trick your nerve endings into thinking they’re experiencing actual heat. That’s why that bowl of curry makes your mouth feel like it’s actually being burned, and why it makes you sweat.
(A similar principle makes mint taste cool — your nerves react to the menthol in it the same way they do to cold temperatures.)
So on a hot day, eating hot foods can make you feel cooler by making you sweat more, and by raising your body temperature — lowering the temperature difference between you and the surrounding air.
It’s tempting to reach for a bowl of ice-cream to give yourself an immediate cool-down, but funnily enough, that can raise your body temperature over longer periods: ice-cream has a lot of tasty fat in it, and your body needs more energy to digest that fat — and creating all that energy will raise your body temperature.
What you drink makes you sweat
A hot mug of tea on a hot day will produce more sweat: not because hot drinks raise your core temperature by any significant amount, but because they activate heat receptors located along your digestive tract, which in turn activate sweating.
So a hot drink can cool you down, but rigorous studies have suggested there’s a big catch to all this: that extra sweat has to be able to evaporate for it to have any cooling effect.
“On a very hot and humid day, if you’re wearing a lot of clothing, or if you’re having so much sweat that it starts to drip on the ground and doesn’t evaporate from the skin’s surface, then drinking a hot drink is a bad thing,” Dr Ollie Jay, a Sydney-based expert in how bodies regulate temperature, told Smithsonian magazine.
“The hot drink still does add a little heat to the body, so if the sweat’s not going to assist in evaporation, go for a cold drink.”
So knocking back a hot chocolate before bed isn’t going to help if you’re dripping with sweat. However, if you’re in conditions where you can sweat efficiently you should favour a hot drink, Dr Jay advised ABC Health.
Intriguingly, in those sweat-friendly conditions an ice-cold bevvy mightn’t help you feel any cooler, because drinking it will shut down the switch on your body’s sweating mechanism (which is thought to lie somewhere in the stomach).
And speaking of ice-cold bevvies, a frosty beer might not have the cooling effect you expect either: alcohol causes your blood vessels to widen, particularly the vessels close to your sin (a process called vasodilation), which warms up your body. That’s why alcohol can make you flushed, and why it’s (falsely) believed alcohol can ward off chilly temperatures.
So on hot days, ice-cream and beer are out — and chilli and tea are in.