The stimulation causes the brain to release serotonin, which intensifies itch. As serotonin spreads from the brain into the spinal cord, the chemical can jump the tracks. It moves from pain-sensing neurons to nerve cells which intensifies the feeling.
Serotonin is involved in growth, ageing, bone metabolism and in regulating mood. People take anti-depressants like Prozac, Zoloft and Paxil, which increase serotonin levels to control depression.
Blocking serotonin would have far-reaching consequences throughout the body, and people wouldn't have a natural way to control pain.
The research, published in the journal Neuron, revealed the events happen in a certain order. First, you scratch, and that causes a sensation of pain. Then the body makes more serotonin to control the pain. But serotonin does more than only inhibit pain. It makes the itch worse by activating GRPR neurons through 5HT1A receptors.
Of course, animals scratch too. I love the shape their body forms while scratching.
From How Stuff Works.
The average human body is covered by about 20 square feet (2 square meters) of skin. Skin is the only organ that is constantly exposed to potential irritation. And, with so many things coming into contact with your skin daily, you're bound to get an itch or two. Serious itching can be caused by allergies, disease, emotions and infections, but let's take a look at what causes the common itches that aggravate you everyday.
Itching, also known as pruritus, starts with some kind of external stimuli, including bugs, dust, clothing fibers and hair. Like tickling, itching is a built-in defense mechanism that alerts your body to the potential of being harmed. In this case, it might be the potential of being bit by a bug.
When the stimuli lands on your skin, it may not bother you at first, but soon it will begin to rub back and forth across your skin. Once the hair or dust scratches your skin's surface layer, receptors in the dermis of the skin will become irritated. In a split second, these receptors send a signal through fibers in the skin to your spinal cord and then up to the cerebral cortex in your brain.
As soon as we feel an itch, our first natural response is to scratch the spot of the itch with our fingernails. The reason for this response is simple -- we want to remove the irritant as soon as possible. Once you've scratched the area of irritation, you are likely to feel some relief. When your brain realizes that you've scratched away the irritant, the signal being sent to your brain that you have an itch is interrupted and therefore no longer recognized by the brain.
Even if you don't remove the irritant, scratching will at least cause pain and divert your attention away from the itching. The irritant that caused the itching is very small, maybe only a few microns in length, so it disturbs only a few nerve endings. When you use your fingernail to scratch the spot where the irritant is, you not only remove the irritant but you irritate a lot more nerve endings than the irritant.
With me, it's the sensation. Nothing stops me from scratching faster than added pain. I've got too much already. Saying that, I found myself scratching under my eye. Will I ever learn?
Now you know what causes the itch, will you be able to override your brain and control the urge to scratch?