h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

why does our skin itch?
why does scratching help?
why does different parts of you start itching just as you have got rid of the itch in one place?
why do you get tingles down your spine if you try to ignore the itch?

Someone else will have to along and answer your questions properly, but in the meantime I can say a little bit about the ithiness phenomenon. A flea bite is itchy because before sucking your blood, the flea injects an enzyme to stop it clotting. This irritates the skin, causing an itch.

I've never noticed spine tinglings when I ignore an itch. Do you think maybe that's just your own mind playing tricks on you?

I was under the impression that itching is related to nerve irritation, but I don't know how true that is.

However, I also sometimes get twitches and tingles if I ignore an itch; for example, if my arm is itching and I ignore it and the itch gets worse, my arm will jump. So Nicky, you're not alone in getting this kind of thing too. I assumed it was something to do with the nerve pathways!

All mammals seem to itch - I've seen dogs, cats, horses and even guinea pigs scratching. Do any animals other than mammals suffer from itches? I can't imagine that anything with tough skin like a snake would have problems, but what about birds?

This might throw some light on the reason why we itch.

Jesus... if snakes can get itches they must be screaming on the inside.

Anyway, how much of itching is psychosomatic? Since finding this thread I've been pretty damn itchy.

Misread Gnomons post... although a snake with an itch would be interesting.

I think we itch as a warning to protect us against ticks, mites and lice.

Scratching possibly helps itches because it's a way of getting the ticks or lice off your skin.

I know I have seen my pet fish scratching on the gravel and rocks in the aquarium. Hope this helps.

itch is apparently carried by the same nerves that carry pain sensation, I haven't heard an explanation as to how that works. and have you noticed that when you scratch, sometimes you itch somewhere else quite distant from the first itch but triggered by it?

yeah and thats annoying.
why is that?

Insect bite itches are mainly caused by your own body's response to the bite. Often insects that bite and suck will inject a substance to prevent clotting. Your body's defences kick in against this and the mechanical damage to release histamine, which is part of a local inflammatory effect - the more histamine, the bigger the inflammation, the greater the itch. This is why anti-histamine tablets and creams work to reduce the maddening itchyness of an insect bite, they are counteracting your immune response.

Can't quite remember about random itches and how they work although it is true that the messages are carried by the same nerves that carry touch so rubbing, pressing or scratching can mask the itch - although in the case of an insect bite scratching merely exacerbates the damage and as soon as you stop scratching the itch will be even worse...

you should spit on insect bites.
it stops the itching

Some itching is caused by the movement of your hairs. This could explain random itching. It might also explain the itch "jump factor," as moving to scratch an itch could disturb hairs on another part of your body.

We're going to publicise this convo on the Front Page tomorrow, by the way

I seem to remember reading somewhere (New Scientist I think, maybe Scientific American) that scratching or rubbing the mirror location of an itch could make it go away. e.g. if you have an itch on your right arm, then scratching your left arm could make it go away.

However, my highly technical experiments in this area (i.e. occasionally doing it when I remember) lead me to believe that this might not always work.

Traveller in Time scratching his head
"--Why do we itch ?
Think it is something basic as pain, your boy tells you there is something unknown wrong, requesting you to take action that way.
Often it will be just a precaution as in scaring away 'bugs' or rubbing away the pointy thing. Also it can be the reaction to something you should not have done: do not touch the stinging nettle, do not use soaps removing all protective moist from your skin, do not use dangerous materials.
The worst will be when the itch is caused by an allergic reaction.

--Why does scratching help ?
Removing of the danger your body warns you for. Or simply: the dead skin cells have been removed.

--Why does different parts of the body itch alternating ?
Basically as when you helped your skin on one place the Alert signal (as that is what an itch is) comes through from less urgent places.

--Surpressing reflexes does generate side effects in trying to distract your mind, letting your hands scratch again

--I have seen scratching by my birds, snakes do as well as their skin comes off, shrimps also scratch as they peel off their old skin.

How contaminating is itching ? Tell the parents waiting for their children to come out of school there have been lice found. In less then five minutes most will start scratching "

"Itch is a sensory stimulus to our body. If a fly happens to sit on your
arms or a mosquito is about to bite you, you have the feeling of itch. It
is, you might say, a modified form of the touch sensation. This sensation
persists till you remove the source stimulus by scratching or rubbing. Too
mutch scratching may also lead to pain, which is believed to inhibit the
sensation of itch." -Ankur Shah, Medical student, Medicine(MBBS), Medical College (taken from
http://www.madsci.org/posts/archives/jun2000/960410788.Me.r.html)

Two thoughts:

Exactly how big is an itch? Difficult to tell, eh?

How many itches do we have on our body at one time? Maybe we have tens or even hundreds below the point of awareness? Try this experiment: get a ruler and scratch your back. Although you weren't aware of having itches on your back you will feel loads of itches being, er, 'killed'.