"One cool thing about Brian Kim's work is he discovered that not only do these molecules bind to itch neurons, but they lowered the threshold for other molecules in the skin to activate itch neurons, so they generally sensitised people with allergies to be more itchy," says Marlys Fassett, professor of dermatology at the University of California, San Francisco.įassett has concentrated on another 'itch cytokine', IL-31, which has also been shown to trigger itch-specific neurons. These chemicals, known as cytokines, also bind to sensory neurons in the skin, causing itch. Meanwhile, in 2017, Brian Kim and colleagues at Washington University's Centre for the Study of Itch and Sensory Disorders, discovered that inflammation in the skin can cause immune cells to release chemical messengers called IL-4 and IL-13. They project directly to the brain and seem to play a pivotal role in transmitting itch. For instance, Mas-related g-protein-coupled receptors are found on sensory neurons that innervate the skin. Since then, researchers have discovered other itch-specific receptors and neurons. In other words, scientists had found a bunch of neurons in the spinal cord that specifically transmit the sensation of itch to the brain. No matter how much they were tickled or irritated, they didn't scratch themselves. Mice without the receptor were incapable of feeling itch. However, in 2007, scientists led by Zhou-Feng Shen at Washington University School of Medicine, St Louis, discovered a dedicated itch receptor on a subset of neurons (nerve cells) in the spinal cord. He found that the initial feeling of pain was followed by an aftersensation of itching. This misconception can be traced back to the early 1920s, when Austrian-German physiologist Max von Frey prodded the skin of his lab participants with minute sharp-pointed objects called spicules. One reason for this is that scientists were convinced that itch was just a mild form of pain. But antihistamines have no effect on chronic itching.Īs a result, there have been few advances in itch treatment for 360 years, when itching was first medically defined. Although annoying, acute itch can be treated with antihistamines or topical steroids. If you get bitten by a mosquito, or come into contact with poison ivy, immune cells in the skin release histamine and other factors, which bind to little receptors on the surface of sensory nerves, causing them to fire and send an itch signal up to the spinal cord and brain. Acute itch, on the other hand, is relatively well understood. However, despite its pervasiveness, until recently scientists didn't really understand what causes chronic itch. From that standpoint it can be considerably more debilitating." Chronic itch is different because it doesn't let you rest. "With chronic pain you have a dull aching sensation – it's like 'six out of 10' pain that just won't go away – but you can sleep. "Studies have shown that chronic itch is equally as debilitating as chronic pain, but I would actually argue it is more so," says Brian Kim, a clinician and neuroimmunologist at the Icahn School of Medicine at Mount Sinai in New York. Some cancer patients stop taking life-saving medications because of the itching the drugs can cause. Patients with liver disease have received transplants because they can't cope with the sensation. That may be something that sufferers of psoriasis can relate to, as itch that comes with this condition has been compared to being attacked by fire ants. In Dante's Inferno, liars were condemned to the eighth ring of Hell where they suffered "the burning rage of fierce itching that nothing could relieve". In some cases, chronic itch can last for years. Chronic itch is associated with dermatologic disorders such as eczema, hives and psoriasis, but also with other medical conditions including chronic kidney disease, liver failure, and lymphoma. The condition is one of many that causes chronic itch – medically defined as an itch lasting greater than six weeks. Shayanne was diagnosed with prurigo nodularis (PN), a chronic inflammatory skin disease which translates as "itchy nodules". I would have to get up to clean myself because there was blood on the sheets." "I couldn't take hot showers, I couldn't focus on my homework at school, I couldn't sleep because I would have to itch for almost two hours in my bed. "I thought at first it could be eczema, but it was so much more debilitating," she says. Shayanne Boulet was 18 and at the end of her first year of college when, out of nowhere, she developed an excruciating itch.
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