Why do we itch? - Emma Bryce
-
0:07 - 0:10You're standing at
the ready inside the goal -
0:10 - 0:14when suddenly, you feel an intense itch
on the back of your head. -
0:14 - 0:18We've all experienced the annoyance
of an inconvenient itch, -
0:18 - 0:23but have you ever pondered why
we itch in the first place? -
0:23 - 0:28The average person experiences
dozens of individual itches each day. -
0:28 - 0:30They can be triggered by all sorts
of things, -
0:30 - 0:32including allergic reactions,
-
0:32 - 0:33dryness,
-
0:33 - 0:35and even some diseases.
-
0:35 - 0:39And then there are the mysterious ones
that pop up for no reason at all, -
0:39 - 0:42or just from talking about itching.
-
0:42 - 0:46You're scratching your head right now,
aren't you? -
0:46 - 0:50Anyhow, let's take one of the most
common sources: bug bites. -
0:50 - 0:51When a mosquito bites you,
-
0:51 - 0:56it releases a compound into your body
called an anticoagulant -
0:56 - 0:59that prevents your blood from clotting.
-
0:59 - 1:01That compound,
which we're mildly allergic to, -
1:01 - 1:04triggers the release of histamine,
-
1:04 - 1:07a chemical that makes
our capillaries swell. -
1:07 - 1:09This enables increased blood flow,
-
1:09 - 1:12which helpfully accelerates
the body's immune response -
1:12 - 1:14to this perceived threat.
-
1:14 - 1:16That explains the swelling,
-
1:16 - 1:20and it's the same reason pollen
can make your eyes puff up. -
1:20 - 1:24Histamine also activates the nerves
involved in itching, -
1:24 - 1:28which is why bug bites make you scratch.
-
1:28 - 1:32But the itchy sensation itself
isn't yet fully understood. -
1:32 - 1:33In fact, much of what we do know
-
1:33 - 1:38comes from studying
the mechanics of itching in mice. -
1:38 - 1:41Researchers have discovered that
itch signals in their skin -
1:41 - 1:47are transmitted via a subclass of
the nerves that are associated with pain. -
1:47 - 1:53These dedicated nerves produce a molecule
called natriuretic polypetide B, -
1:53 - 1:57which triggers a signal that's carried
up the spinal cord to the brain, -
1:57 - 2:01where it creates the feeling of an itch.
-
2:01 - 2:04When we scratch, the action of our
fingernails on the skin -
2:04 - 2:10causes a low level pain signal
that overrides the itching sensation. -
2:10 - 2:15It's almost like a distraction,
which creates the sensation of relief. -
2:15 - 2:20But is there actually an evolutionary
purpose to the itch, -
2:20 - 2:23or is it simply there to annoy us?
-
2:23 - 2:28The leading theory is that our skin
has evolved to be acutely aware of touch -
2:28 - 2:32so that we're equipped to deal with risks
from the outside world. -
2:32 - 2:33Think about it.
-
2:33 - 2:37Our automatic scratching response
would dislodge anything harmful -
2:37 - 2:40that's potentially lurking on our skin,
-
2:40 - 2:41like a harmful sting,
-
2:41 - 2:43a biting insect,
-
2:43 - 2:46or the tendrils of a poisonous plant.
-
2:46 - 2:49This might explain why we don't
feel itching inside our bodies, -
2:49 - 2:51like in our intestines,
-
2:51 - 2:53which is safe from these external threats,
-
2:53 - 2:57though imagine how
maddening that would be. -
2:57 - 3:01In some people, glitches in the pathways
responsible for all of this -
3:01 - 3:06can cause excessive itching
that can actually harm their health. -
3:06 - 3:11One extreme example is a psychological
condition called delusory parasitosis -
3:11 - 3:16where people believe their bodies
are infested with mites or fleas -
3:16 - 3:18scurrying over and under their skin,
-
3:18 - 3:22making them itch incessantly.
-
3:22 - 3:24Another phenomenon
called phantom itching -
3:24 - 3:28can occur in patients
who've had amputations. -
3:28 - 3:32Because this injury has
so severely damaged the nervous system, -
3:32 - 3:35it confuses the body's normal
nerve signaling -
3:35 - 3:40and creates sensations in limbs
that are no longer there. -
3:40 - 3:45Doctors are now finding ways
to treat these itching anomalies. -
3:45 - 3:49In amputees, mirrors are used to reflect
the remaining limb, -
3:49 - 3:52which the patient scratches.
-
3:52 - 3:54That creates an illusion
that tricks the brain -
3:54 - 3:59into thinking the imaginary
itch has been satisfied. -
3:59 - 4:02Oddly enough, that actually works.
-
4:02 - 4:06Researchers are also searching
for the genes involved in itching -
4:06 - 4:09and developing treatments to try
and block the pathway of an itch -
4:09 - 4:12in extreme cases.
-
4:12 - 4:17If having an unscratchable itch
feels like your own personal hell, -
4:17 - 4:19Dante agreed.
-
4:19 - 4:21The Italian poet wrote about
a section of hell -
4:21 - 4:29where people were punished by being
left in pits to itch for all eternity.
- Title:
- Why do we itch? - Emma Bryce
- Speaker:
- Emma Bryce
- Description:
-
View full lesson: http://ed.ted.com/lessons/why-do-we-itch-emma-bryce
The average person experiences dozens of individual itches each day. We’ve all experienced the annoyance of an inconvenient itch — but have you ever pondered why we itch in the first place? Is there actually an evolutionary purpose to the itch, or is it simply there to annoy us? Emma Bryce digs deep into the skin to find out.
Lesson by Emma Bryce, animation by Sashko Danylenko.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 04:44
Takamasa Omata commented on English subtitles for Why do we itch? | ||
Jessica Ruby approved English subtitles for Why do we itch? | ||
Jessica Ruby accepted English subtitles for Why do we itch? | ||
Jessica Ruby edited English subtitles for Why do we itch? | ||
Jennifer Cody edited English subtitles for Why do we itch? |
Takamasa Omata
1:47-1:53 "These dedicated nerves produce a molecule
called natriuretic polypetide B,"
I think "polypeptide" is more appropriate spelling.