I never actually knew what itching was for, so I looked it up. According to this article, its thought to be an evolutionary mechanism that is sending the signal something is happening on your skin thats like a bug crawling on your skin, so go flick that bug off before it bites you. (Of course, as is often the case with such mechanisms, it generates more false alarms than genuine ones.)
Interesting. But this next paragraph bugged me (pun not originally intended):
The same fibers that send itching signals are also used to send pain signals to the brain, which once led some scientists to believe that itching was a form of light pain. That notion has since been dispelled by research, which showed that pain and itching elicit opposite responses. Pain causes us to withdraw and itching causes us to scratch.
Now I havent read the research the article refers to; there may be better arguments in it than the one described here. But the one described here is not impressive.
First, and most obviously: pain just doesnt always cause us to withdraw; sometimes it does, but there are many different kinds of pain. People usually clutch their heads when they have headaches, for example; thats the opposite of withdrawing.
Moreover, even if, counterfactually, all pains did in fact cause withdrawal behaviour, its not obvious that this fact should be regarded as part of the essence of pain. Whats essential to pain, surely, is that it makes us want to avoid doing whatever causes the pain; but wanting to avoid touching the location of the pain seems a distinct and accidental feature (since touching the location of the pain does not always necessarily increase the pain).
In any case, if you find that case X differs from standard cases of Y by lacking feature Z, youre then faced with a choice of either denying that X is a Y or denying that feature Z is essential to being a Y. In this case, then, scientists were faced with the choice between either denying that withdrawal behaviour is essential to pain or denying that an uncomfortable sensation that inherently makes us want to get rid of it counts as a pain. Which is the more plausible choice?
More broadly, while the question of what physiological mechanisms underlie pain is presumably an empirical, natural-scientific question, the question of whether a particular kind of sensation is a pain seems more like a conceptual, philosophical question to which scientific research is irrelevant.
Heres my argument for that claim. Suppose that scientific experts announced tomorrow that headaches are not actually a form of pain. (I choose headaches because theyre more paradigmatically a form of pain than itches.). Headaches may feel like pains, these experts aver, but theyre really not pains, because they involve neuronal thingummy B instead of neuronal thingummy A. Would you take this seriously? Surely not, because feeling like pain is simply what we mean by pain its part of the conceptual grammar of the term. Anyone who talks of somethings feeling like pain but not being pain would have to be using the word pain with a new, nonstandard meaning, just as someone who talked of somethings being a regular quadrilateral but not a square would have to be using the word square with a new, nonstandard meaning. (Or else using some of the other words in the sentence nonstandardly.)
The researchers described in this article may well have confused constitutive with enabling conditions. And that takes me to a broader grump about scientists, namely, that scientists tend to be unaware that there is such a thing as a philosophical objection to a thesis. They tend to assume that anything that sounds like a coherent hypothesis (such as the possibility of time travel, or the suggestion that the universe we live in is actually 2-dimensional to pick a couple of actual examples) is thereby fit for empirical investigation, without considering that in such cases a) there is a prior question as to whether the thesis so much as makes sense (for if it does not, then those who take themselves to be performing an empirical investigation of it will actually not be investigating anything or at least not that), and b) the training and tools to determine whether it does makes sense are the specialisation of a field other than their own.
(But then, a still more egregious problem is the philosophers who are confused about this.)