Why do we Itch?
Does looking at this make you itchy? Image Credit: Paka via Flickr
You know that feeling? There’s an itch, but no matter how hard or how much you scratch it, you just can’t relieve it?! We’ve all had itches; it’s a phenomenon that has occurred throughout history. But why do we itch? What’s the evolutionary advantage? And how can we stop it?
Mosquitoes inject a chemical that causes a mild allergic response. Image Credit: Chris Fifield-Smith via Flickr
There are several causes of itching, including allergies, dryness and illness, but there are also some itches for which the cause is still being speculated. The most common form is caused by a small scale allergic response. Let’s say, for example, you’re at a BBQ in the middle of Summer. You’ve forgotten the Aeroguard and low and behold, you’ve been eaten alive by mosquitoes (I think we can all relate). Whilst mozzies are sucking your blood (pardon my bluntness), they release an anticoagulant into your bloodstream. This chemical stops the blood from clotting and makes it easier for the mozzies to suck up more. Humans are mildly allergic to anti-coagulant; hence its release triggers the release of histamine, the neurotransmitter responsible for human allergic responses. Histamine increases blood flow to the bite, increasing the immune response and causing the region to become inflamed. You know that itchy red bite that mozzies leave? Well that’s the inflammation. Histamine also stimulates several nerves which create that itchy feeling on the skin. The extent to the itching feeling are still somewhat unknown, however it is believed that the nerves creating the feeling are associated with the same nerves that transmit pain.
So sure, that’s the main cause, but why do we feel the urge to scratch that itch? There are a couple of theories. If we look at it physiologically, the act of scratching a region of itchy skin transmits faint signals like that of pain, that overcome the outcoming pain signals of the itch. This provides relief and acts as a distraction to the pain for the brain. However, If we view the problem form an evolutionary perspective, scratching or rubbing an itchy patch of skin may be a way of defending against bugs or parasites that may be causing the itch, e.g. that pesky mozzie!
Scientists are still conducting research into the itchy phenomenon. A particular region of interest is into phantom itches in patients who have had limbs amputated. Similar to the principle of phantom pains, phantom itches are felt by amputees where their limb use to exist, however, there is no way of relieving the urge. A few methods have been introduced to relieve the itching, such as using a mirror to watch themselves itch that region where the limb once existed. This method has been unexpectedly successful, however other techniques are being explored.
So next time you get to itch yourself, stop and think: what’s actually happening inside to trigger this response? But then, itch way, because for now we’re stuck with it.