One of the most torturous feelings is having an itch that you cannot scratch. But how do you describe the feeling of an itch? To me, it is as if tiny invisible entities are having a dance fest on parts of my skin.
We have only come to understand the medical dimension of an itch during the later part of the 19th century. Before that, we dealt with itching as mostly as a light, temporary condition that is part of our bodily experiences. Superstition has also been recruited to make sense of what itches could mean. You have heard of itchy palms to mean you will have money coming soon or itchy feet to mean you are going on a trip or itchy ears to signify that someone is talking about you, good or bad. As for metaphors, an “itchy tongue” has always signified one who can’t keep a secret and spilling the beans will be the “scratch” that would give it relief.
Bu the main scientific understanding we have had of an itch has to do with the effect of something “foreign” like a bug or material, coming into contact with your skin that your skin recognizes as “alien” and alerts your immune system to produce histamines.
Histamines are receptors and receptors are like paparazzi – cells which are so attuned to reacting to stimuli (be it light, touch, smell, sound) and send signals throughout our body and brain so we could respond. In the case of itching, histamines open up another receptor, TRPV1, that causes the nerve endings to fire which you feel as an itch. This is why most anti-itch drugs are called anti-histamines. Feeling an itch is a reaction that nature came up with in our wiring to protect us because when you feel an itch, you will scratch. Scratching will eventually get rid of the bug that bit you and then ah, you get the incomparable relief you feel. But why does it feel so good to scratch an itch?
Scratching apparently makes our spinal chords release our own natural opioids – those that calm the brain region called the anterior cingulate cortex which is frenzied when we feel an itch. Research in the past few years has found that itch is so related to pain in terms of how closely their receptors sit in relation to each other. Thus, when we scratch an itch, we also release serotonin which also eases pain and since the itch and pain receptors are seatmates, the itch receptors get touched too and thus, the itch reoccurs. This is how scratching oftentimes causes more itching.
What is even more interesting is what is starkly animated in our brains when we scratch. Scientists have found that when we scratch an itch, our reward centers light up which indicates that scratching gives pleasure as well as relief.
But itching also occurs in people who have not come in contact with any foreign external substances that trigger histamines. Chronic itching happens to people who take some medication, have kidney failure, some cancers or even stress.
For the past few years, research has yielded another path related from the known mechanism. A piece in the latest issue of Scientific American has cited these studies which found another receptor, aside from histamine which also opens up another receptor related to the known path, TRPA1 that causes the nerve endings to fire and cause you to itch. This is the same receptor that is also activated by heat and capsaicin (the active ingredient in chili peppers which gives it that wild potency). The effects of “heat” and “capsaicin” are considered “pain”by the body. This is what happens when you take an anti-malaria medication called chloroquine. Anti-histamines will not help relieve itching for this because histamines are not the ones causing you to itch.
Sensations are both the costs and rewards of being alive. It is turning out that itching – which we have largely viewed as a non-threatening, albeit annoying and uncomfortable – is, like most things revealed by understanding, more complex than we thought. It is literally tied tied to the drama of our lives – to feelings of pleasure and pain. It explains why you feel you can’t move on if you have not scratched an itch and why when you start scratching, it is difficult to stop. Science has literally scratched “itch” beyond the surface. – Rappler.com
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