Reasons Why You Itch

Having an itch can be a pretty nasty thing, severe itches can be caused by bug bites, sunburn and poison ivy. Millions of people around the world suffer from a skin condition called dermatitis, where an individual’s skin becomes very dry and itchy, when they come into contact with certain things such as laundry detergent and jewellery. Some people who have atopic dermatitis, a type of eczema, actually scratch during their sleep.

In many cases sufferers of chronic itches will uncontrollably scratch themselves until they bleed. According to Martin Schmelz, a neurophysiologist at the University or Mannheim in Germany “Quality of life is decreased by itch to the same degree as it is by pain”. But people don’t have nearly as much empathy for those with a chronic itch as those with pain. About 9% of people have some sort of chronic itch problem.

So finding a cure for itching would be a medical revolution, there is actually a conference dedicated to this subject called the International Workshop for the Study of Itch, which hundreds of scientists and researchers attend. Because even though there have many small advances in the field, itching is still a bit of a mystery and we’re still a long way from a cure.

But an itch isn’t just a form of mild pain, pain causes us to recoil. Whereas an itch just gives us an unpleasant desire to scratch. Itching has it’s own matrix of nerves and chemicals, completely separate from those used to relay pain.

But why do we itch?

Luckily for us itching can only occur in the top two layers of our skin, we can’t get internal itches, thank God.

Animals develop itches when they have bugs and parasites on their skin, itching is a natural defence mechanism against these insects, which can give the animals infections. Animals scratch to remove the bugs because their body has signalled to them, via an itch, that something very small is attacking them. One widely adopted theory is that we itch because we still have a primate instinct to do so. A defence mechanism such as this is an evolutionary advantage, so it make sense for our bodies to keep it. After all we aren’t safe from parasites either. So ultimately we itch to defend ourselves from parasites and infection or anything which could irritate our skin, such as stinging nettles.

When we get an itch, dedicated cells around the affected area release an organic nitrogen compound called histamine. These histamines send signals to our brain, more specifically the cerebral cortex which controls our conscious thoughts, our cerebral cortex then tells us we have an itch. Antihistamines work by stopping the histamines from reaching their receptors.

But why does scratching relieve an itch?

Scratching the skin blocks activity of the cells in the spinothalamic tract, a sensory pathway originating in the spinal cord. This lack of activity prevents the spinal cord from sending signals to our brain that we have an itch. Therefore the itch stops.

People who have had a limb amputated experience a syndrome called “phantom limb”, where the amputee feels severe itching where the limb used to be. This phenomenon occurs in over 90% of amputees.

Itching is contagious, when we see someone else scratching themselves we develop itches from nowhere. In a recent studies, by researchers at the universities of Hull and Sussex, in the UK, participants where shown videos of people scratching their bodies. 64% of the test subjects scratched themselves whilst watching the videos. You can even manifest itches by just thinking about itches, in fact you’re probably feeling itchy whilst watching this video. But why?

In MRI scans researchers found that when people see others scratch, the parts of their brains associated with having an itch were activated. It’s not empathy that causes this, we don’t feel sorry for the person with an itch. It’s neuroticism; neuroticism is the tendency to feel negative emotions. In the studies the people who were the most neurotic suffered the most from contagious itching.


Source: Thoughty2

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