Why Do People Itch?

Itching is defined as a sensation that causes a reflex or the desire to scratch and bears many similarities to pain. Both are unpleasant sensory experiences but they have different behaviour response patterns. This post will attempt to explain what causes itching and why people have the urge a scratch an itch.

Feeling a random itch on the back of your head or your arm is something we have all experienced and is often inconvenient but most of us do not actually know why we itch in the first place. The normal person experiences dozens of itches every day, triggered by all sorts of things such as dryness, allergic reactions, some diseases, and even the mysterious itches with no clear cause. Here we’ll look at a few different aspects of itching:

  • Bug Bites
  • Nervous System Response
  • Psychological Response

Bug Bites

One of the most common causes of itching is bug bites. When a mosquito bites a person, it releases a compound into their body called an anticoagulant, which prevents blood from clotting. That compound, which we are mildly allergic to, triggers the release of histamine, a chemical that makes our capillaries swell. This enables increased blood circulation and flow, which beneficially accelerates the body’s immune response to this perceived threat. That explains the swelling, and it’s the same reaction that occurs when pollen makes your eyes puff up.

Histamine also activates the nerves involved in itching, which is why bug bites make you want to scratch. The itchy sensation itself isn’t yet fully understood, and much of what we do know comes from the study of the mechanics of itching in mice. Researchers have discovered that itch signals in skin are transmitted via a subclass of the nerves that are associated with pain. These nerves produce a molecule called natriuretic polypeptide B, triggering a signal that’s carried up the spinal cord to the brain, creating the feeling of an itch itself through a complex nervous system.

Nervous System Response

The actual scratching action of our fingernails against our skin causes a low level pain signal that overrides the itching sensation. It’s almost like a distraction that creates the sensation of relief. The question here is whether or not there is actually an evolutionary purpose to the itch, or is just simply an annoyance? The main theory is that our skin has evolved to be finely aware of touch so that we’re equipped to deal with external risks from the outside world.

Our automatic scratching response would remove anything harmful that’s potentially lurking on our skin, like a harmful sting, the tendrils of a poisonous plant or a biting insect. Our skin is a barrier that acts as lines of defence, protecting us from harmful microorganisms which could potentially enter our skin. This might explain why we do not actually feel itching inside our bodies, like in our intestines or heart, which are safe from these external threats, because it would be absolutely maddening to us if our own organs would start to itch.

Psychological Itching

For some people, glitches in the pathways or mutations in our nervous system responsible for this complex process can actually cause excessive itching and has the potential to actually harm their health. One extreme example is a psychological condition called delusory parasitosis where people believe their bodies are infested with fleas or mites that scurry all over and under their skin, making them itch constantly and incessantly.

Another phenomenon that can harm a person’s health is called phantom itching, occurring in patients who have had amputations. An amputation severely damages the nervous system, confusing the body’s normal nerve signaling and creating itching sensations in limbs that are no longer there. Doctors have been seeking new ways to treat this phantom itching. One method that is surprisingly effective is using mirrors to reflect amputees’ remaining limb into the space where the amputated one should be, thus allowing them to scratch that particular area. This trick creates an illusion, tricking the brain into believing that the imaginary itch has been scratched and satisfied.

Researchers are always searching for genes involved in the process of itching in order to develop treatments to prevent the blockage of these pathways in these extreme cases where individuals are itching incessantly or for no particular reason.

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