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The American poet Ogden Nash said, “Happiness
is having a scratch for every itch.”

But while scratching can feel pretty good,
we all know what happens next.

When considering scratching an itch, it may
be better to follow the old Yiddish proverb:

“A quarrel is like an itch; the more you
scratch, the more it itches.”

There are plenty of things that cause that
irritating, unpleasant, itchy sensation.

But why do we itch in the first place?
[OPEN]
The itch sensation, also known as pruritus,
is not the most pleasant thing, but it evolved

for a good reason.
Stretched out, your skin covers about 20 square
feet, the biggest organ you have.

Your other organs on the inside are protected
by your immune system, but, skin is your first

line of defense, the wall that guards the
human realm, exposed to the elements, and

it’s got a unique way to deal with different
types of threats.

Where there’s an itch, there’s a desire
to scratch, often an unconscious desire.

This reflex likely prompted our outdoor-dwelling
ancestors to remove parasitic threats and

other irritating things like thorns and allergens.
And much like yawning, being itchy is thought
to be contagious, as some of you may be noticing

right about now.
We are social animals, dcB.B.so watching some
infested tribe mate get their scratch on could

have given us a head start to get rid of those
parasites.

So, we know the purpose of itch.
But what happens inside our bodies that makes
it feel different from other sensationsffevv

like pressure or heat?
Turns out, we don’t know all the pieces
to the itch puzzle yet.

Up until about a decade ago scientists thought
itch was just a dialed down, less intense

version of pain.
When something makes contact with our skin,
nerve endings in the epidermis–the outermost

layer of our skin– relay this information
through electrical and chemical messages,

up the spine and to the brain.
Different stimuli activate different nerve
pathways and cause different sensations in

our brains.
Light touch might feel nice.
A punch to the face will probably hurt.
We now know that there’s special itch-specific
circuitry in our nervous systems, involving

its own chemicals and cells.
And we share one universal response to itching:
scratching.

And boy does it feel good.
But, why?
Scratching, is technically a form of pain.
I mean, the name of a small wound that breaks
the skin *is* a* scratch.

Scratching causes a low-level pain signal
to the brain that masks and overrides the

itch signal, which is why slapping, pinching,
and pressing itchy regions also gives you

relief.
Remember that the next time your mom tells
you not to scratch.

Your brain responds to pain by triggering
the release of chemicals at the irritated

site, which tunes down the painful sensation.
One of those relief-providing chemicals is
serotonin, a neurotransmitter.

But that serotonin also makes it easier for
the itch signal to be re-triggered again.

So, the itch nerves fire again and you get
even itchier!

Scientists call this constant loop of itching
and scratching the “itch-scratch cycle”–very

clever–and it can be maddening.
In extreme cases, damage to itch-sensing nerves
can cause itching without an actual stimulus,

and this is the kind of itch that scratching
can’t help.

People who have recovered from shingles, a
virus infection that affects your nervous

system, can be left with an unexplainable,
never-ending itch once the rash recedes.

One women had such an itchy scalp after healing
from shingles that she scratched straight

through to her brain.
So, what can the rest of us do to avoid scratching
a`n itch?

Itchy ailments have been documented throughout
history, and humans have found some pretty

clever ways to find relief.
The Greeks and Romans had mineral baths and
animal fat.

The Persians used silver.
Menthol soothed itchy skin in ancient China,
and camphor, a chemical from Evergreen trees

historically used to make explosives, has
been soothing itchy skin since the 13th century.

Today we also have anesthetics, which numb
the skin of all feeling, counterirritants

like capsaicin, extracted from chili peppers,
and antihistamines and steroid creams, just

to name a few.
But since itchiness can be caused by so many
things there isn’t a one-size-fits all remedy.

Luckily, with so many treatments to choose
from, at least you don’t have to start from

scratch.
If you’re itchy, just remember: Unlike beauty,
itch doesn’t run only skin deep.

It’s a sensation that reaches from the epidermis
to the brain.

The origins of that itch you’re feeling
right now extend way back on the evolutionary

tree, and we’ve only scratched the surface
of knowing

how it all works.
Stay Curious.
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這裡癢那裡癢!到底為什麼會發癢?! (Why Do We Itch?)

124 分類 收藏
April Lu 發佈於 2019 年 3 月 15 日
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