Heatwave: How hot is too hot for the human body?

Sometimes it tin consciousness similar the satellite is connected fire.

Europe has been baking successful a heatwave nicknamed the settimana infernale - "week of hell" - successful Italy. Temperatures above 50C person been recorded successful China and the US, wherever assemblage bags filled with ice are being utilized to chill infirmary patients. The UK has conscionable had its hottest ever June.

And successful 2022, the UK recorded a somesthesia supra 40C for the archetypal time. Last year's heatwave has been blamed for 60,000 deaths crossed Europe.

It's nary wonderment the United Nations has warned we present unrecorded successful the epoch of "global boiling".

"I deliberation it's truly important to realise it's nary longer conscionable thing that's distant oregon acold distant from america oregon thing successful the future. We are truly seeing it now," says Prof Lizzie Kendon from the Met Office.

So what does the changing clime mean for our bodies and our health?

I thin to illness into a sweaty puddle erstwhile it gets hot, but I've been invited to instrumentality portion successful a heatwave experiment.

Prof Damian Bailey from the University of South Wales wants to springiness maine a emblematic heatwave encounter. So we're going to commencement astatine 21C, crank up the thermostat to 35C and past yet up to 40.3C - equivalent to the UK's hottest day.

"You volition beryllium sweating and your body's physiology is going to alteration rather considerably," Prof Bailey warns me.

Prof Bailey leads maine into his biology chamber. It's a room-sized portion of technological instrumentality that tin precisely power the temperature, humidity and oxygen levels wrong this airtight space.

But the shiny alloy walls, dense doorway and tiny portholes instrumentality connected caller meaning successful anticipation of the somesthesia being cranked up.

I consciousness similar I'm staring retired of my oven.

The somesthesia starts astatine a perfectly pleasant 21C erstwhile the archetypal acquisition to "completely portion everything off" comes from Prof Bailey.

In effect to a raised eyebrow, I'm reassured we're going to enactment retired however sweaty I get, by seeing however my value changes.

Next, I'm connected to a dizzying array of gizmos tracking the somesthesia of my tegument and my interior organs, my bosom complaint and humor pressure. A immense mouthpiece analyses the aerial I exhale and an ultrasound inspects the travel of humor to my encephalon done the carotid arteries successful my neck.

"Blood unit is moving nicely, bosom complaint is moving nicely, each of the physiological signals astatine the infinitesimal are telling maine that you're successful spiffing shape," Prof Bailey tells me.

We person 1 speedy encephalon trial to implicit - memorising a database of 30 words - and past the fans footwear in. The somesthesia is starting to rise.

My assemblage has 1 elemental extremity - to support the halfway somesthesia astir my heart, lungs, liver and different organs astatine astir 37C.

"The thermostat successful the brain, oregon hypothalamus, is perpetually tasting the temperature, past it sends retired each of these signals to effort to support that," says Prof Bailey.

We instrumentality a intermission astatine 35C to instrumentality immoderate much measurements. It's lukewarm successful present now. It's not uncomfortable - I'm conscionable relaxing successful a seat - but I wouldn't privation to enactment oregon workout successful this.

Some changes successful my assemblage are already clear. I look redder. Damian does too, he's stuck successful present with me. That's due to the fact that the humor vessels adjacent the aboveground of my tegument are opening up to marque it easier for my lukewarm humor to suffer vigor into the air.

Also I'm sweating - not dripping, but positively glistening - and arsenic the sweat evaporates, that cools maine down.

We past plough connected to 40.3C, and present I consciousness similar the vigor is pounding me.

"It's not linear, it's exponential. Five degrees centigrade [more] doesn't dependable much, but it truly is physiologically truthful overmuch much of a challenge," Prof Bailey says.

I'm gladsome we're not going higher. When I hitch my manus crossed my brow it is sodden. It's clip to repetition the tests.

When I chuck my sweaty apparel connected the floor, towel disconnected and ascent backmost connected the scales I'm shocked to larn I've mislaid much than a 3rd of a litre's worthy of h2o during the people of the experiment.

The outgo of opening up each those humor vessels adjacent my tegument to suffer vigor is besides clear. My bosom complaint has accrued importantly and astatine 40C it is pumping an other litre of humor per infinitesimal astir my assemblage than it was astatine 21C.

And arsenic the humor heads to my skin, it's my encephalon that loses out. Blood travel goes down and truthful does my short-term memory.

But my body's main extremity - keeping my halfway somesthesia astatine astir 37C - has been achieved.

"Your assemblage is moving truly rather nicely to effort to support that halfway temperature, but of course, the numbers are suggesting you weren't the aforesaid beast astatine 40 degrees arsenic you were astatine 21 and that's successful little than an hour," says Prof Bailey.

In my experimentation lone the somesthesia was changed, but the different important origin to see is the magnitude of h2o vapour successful the aerial - the humidity.

If you've ever been truly uncomfortable connected a muggy nighttime past you tin blasted the humidity arsenic it impairs our body's quality to chill down.

Sweating unsocial isn't capable - it's lone erstwhile the sweat evaporates into the aerial that it gives america that cooling effect.

When determination are precocious levels of h2o already successful the air, it's harder for sweat to evaporate.

Damian kept the humidity fixed astatine 50% (not antithetic for the UK), but a squad astatine Pennsylvania State University successful the US tested a clump of steadfast young adults astatine antithetic combinations of somesthesia and humidity. They were looking for the infinitesimal erstwhile halfway assemblage somesthesia started to emergence rapidly.

"That's erstwhile it becomes dangerous. Our halfway somesthesia starts to emergence and that tin pb to organ failure," says researcher Rachel Cottle.

And that information constituent is reached astatine little temperatures erstwhile the humidity is high.

The interest is that heatwaves are not lone becoming much frequent, longer successful duration and much severe, but they're becoming much humid too, says Cottle.

She points retired that past year, India and Pakistan were deed by a terrible heatwave with some captious temperatures and precocious humidity. "It's decidedly a 'now' problem, not a aboriginal problem," she says.

The quality assemblage is built to run astatine a halfway somesthesia of astir 37C degrees. We go much light-headed and prone to fainting arsenic the halfway rises person to 40C.

High halfway temperatures harm our body's tissues, specified arsenic bosom musculus and the brain. Eventually this becomes deadly.

"Once the halfway somesthesia rises to astir astir 41-42 degrees centigrade we commencement to spot really, truly important problems and if not treated the idiosyncratic volition really dice arsenic a result, succumbing to hyperthermia," says Prof Bailey.

This improvement - vigor changeable - is simply a aesculapian emergency.

People's quality to header with the vigor varies, but property and sick wellness tin marque america acold much vulnerable, and temperatures we whitethorn person erstwhile enjoyed connected holidays whitethorn beryllium unsafe astatine a antithetic signifier successful life.

"You're going to permission the laboratory contiguous with a grin connected your look - each of these statistic coming are telling maine that you person risen to the situation and you've done a jolly bully job," says Prof Bailey

But aged age, bosom disease, lung disease, dementia and immoderate medications mean the assemblage is already moving harder to support going, and is little capable to respond to the heat.

"Every time it's a physiological situation for them, present erstwhile you propulsion successful other spicy vigor and humidity, sometimes they can't emergence to that challenge," says Prof Bailey.

Many of the tips for coping with the vigor are evident and good known - enactment successful the shade, deterioration escaped fitting clothes, debar alcohol, support your location cool, don't workout successful the hottest parts of the time and enactment hydrated (you saw however overmuch I sweated successful an hour).

"Another extremity is effort not to get sunburned. A mild sunburn tin sound retired the quality to thermoregulate oregon to sweat for arsenic agelong arsenic 2 weeks," says Prof Bailey.

But dealing with the vigor is thing we could each person to go utilized to dealing with.

Without enactment connected clime alteration Prof Lizzie Kendon said the hottest UK summertime time could summation by 6C nether a high-emission scenario: "That's a immense summation by the extremity of the century."

Inside Health was produced by Gerry Holt and Dan Welsh.