are challenging themselves

to stay underwater

for as long as possible.

Some go for half a day

while others

manage to spend

an entire week fully submerged.

What would happen

to your body

if you tried this challenge.

Would your skin fall off?

On today's challenge,

we're going to find out.

In 2006,

David Blaine challenged himself

to be underwater

for a full seven days.

He trained with the Navy SEALs

to lose 23 kg (50 lb),

so his body

would require less oxygen.

But we're dropping you

into this challenge

right away,

with no training at all.

Is this something

you'd be able to handle?

The moment you go underwater,

you'd use less oxygen and

therefore could stay

submerged longer.

As your heart slowed down,

your blood would be diverted

to essential organs that

need oxygen the most,

like your brain,

heart and,

kidneys.

This shunting

is called

peripheral vasoconstriction.

Okay, you're thirty seconds in.

At this point,

you would want to breath again.

You could keep holding your breath

for two minutes

if you're trained for

underwater emergencies but,

past that time,

you'll need to be

assisted by a breathing device.

If you're a free diver,

you'd be able to keep going

for more than 10 minutes.

To do so,

you would have expelled

carbon dioxide out of your lungs

by hyperventilating.

Okay, now that your body

is saturated with oxygen

you'd want to avoid any activity

in order to slow down

your heart rate.

Just stay still as much as possible.

After a five-minute

exposure to water,

your skin would prune,

especially your fingers and toes.

These aquatic wrinkles happen

because of the narrowing

of blood vessels in your skin.

This shrinking

is called digital vasoconstriction

But,

this is nothing

you haven't experienced before.

Let's keep going.

If you spent these

past twenty minutes

without any breathing device

there's a high chance

you'd experience brain damage.

The steady build-up of

carbon dioxide in your blood

would turn it

into an acidic brew.

Muscle spasms

and disorientation could follow,

as well as

a racing heart

and ultimately,

death.

So, to avoid all that,

you'll need a scuba tank

if you have

any hope of

finishing this challenge.

Okay, now that you have some

pure oxygen,

you think this challenge

will be easier right?

Well,

I'm not that sure.

After seven hours

of soaking,

you could suffer from hypothermia.

If the water temperature

drops below

your body temperature

would dip down to

or lower.

You'd start to shiver,

and your pulse would be weak

The cold would

affect your organs,

especially your heart

and nervous system.

You could eventually

go unconscious.

With no warm-up,

hypothermia can lead

to your entire respiratory system

shutting down

and your death.

So for your survival,

the water temperature

should be kept around

Okay, after 24 hours of

of underwater life.

you'll notice some bubbles

forming on your skin.

These are known as vesicles.

They develop because

water becomes trapped

between your outer

and middle layers of skin.

They will continue to form

the longer you stay in the water,

and eventually burst.

And now,

as you finally

finish this challenge,

and get out of the water,

your skin

would start to

peel away

from the popped vesicles.

You'd need medical attention

immediately

as you'd likely have

a severe headache

along with other health issues.

Okay sure,

you managed to make it

out of this challenge alive but

it definitely wouldn't be worth it.

If you want to relax,

I've heard

that withstanding the cold

can enhance your well-being.

Want to give it a try?

Okay,

we'll see what that challenge brings

on another episode of