Why Does Scratching Make Itching Worse?

iStock/champja
iStock/champja

It feels like a biological blooper: A persistent itch is made worse by scratching, the one thing that provides instantaneous relief. Evolutionary biologists have proposed that the relationship between scratching and itching developed when disease-carrying parasites and insects bit humans, causing itching skin; scratching brushed the bugs away. Anyone suffering from a mosquito bite can understand that connection.

There’s no simple answer for why skin that has just been scratched becomes even itchier, but researchers have identified some mechanisms behind the irritating phenomenon.

Why Scratching an Itch Doesn't Help

Our sensory neurons are constantly bombarded with stimuli, so some sensations take precedence over others. Sensory signals of one type can be overridden by signals of other types if the latter are strong enough. The overridden signals don’t even reach the brain—they’re stopped by specific neurons in the spinal cord. In this way, the pain caused by scratching is often sufficient to drown out the itch—but only temporarily.

Cells in the brain stem produce the neurotransmitter serotonin, which quells pain. But according to Zhou-Feng Chen, Ph.D., director of the Center for the Study of Itch at Washington University School of Medicine in St. Louis, Missouri, serotonin has an additional function. His group has found that as the serotonin spreads through the spinal cord, it can activate neurons that transmit itch signals to the brain, compelling us to scratch even more.

Each time we scratch, we put this cycle in motion. The increasing amount of serotonin may even make us scratch harder, until the urge to scratch becomes detached from any itch trigger on the skin. “It’s to try to suppress the itchy sensation, which occurs in your brain,” Chen tells Mental Floss. By this mechanism, itches can even become chronic.

Serotonin signaling isn’t the only way scratching worsens an itch; harm to the skin caused by scratching is another contributor. “When the skin barrier is irritated or further damaged, it releases certain pro-inflammatory factors that can directly aggravate itch by stimulating the sensory nerve fibers,” Brian Kim, M.D., co-director of the Center for the Study of Itch, tells Mental Floss. Those factors can also activate your immune system, and some types of immune cells around the affected area may produce chemicals that induce itch.

The very idea of scratching can also be a trigger. Chen’s research group reported last year that mice appear susceptible to scratching when they see other mice do the same. “Itching is actually contagious between people, between animals, and in your body itself,” Chen says. “When you scratch one place, you quickly want to scratch another area.” Scratching doesn’t just make itch more intense—it sometimes also causes the sensation to spread.

Relief for Itching

In mild cases, it may be possible to resist scratching through sheer force of will—but that’s not usually a long-term solution.

“I always feel bad because a lot of people say to patients, ‘Don’t scratch, don’t scratch,’ but that’s very challenging,” Kim tells Mental Floss. He says he tries to determine the cause of a person’s itchiness first. If it’s caused by an underlying medical problem, such as infestation with lice or liver disease, managing that issue may resolve the itch. Even if the underlying problem can’t be cured, there are medications that can calm itch in certain circumstances, such as antihistamines for allergy-induced itch and topical corticosteroids for itch caused by certain skin conditions, including eczema.

For now, drugs like these may be our best weapons against itching. “I think itch is often viewed as quirky, not serious, or embarrassing,” Kim says, which explains why there’s little research on itch despite its impact on our lives. Unfortunately, that coveted scratch in a bottle remains out of reach.

Chronic Pain Happens Differently in Men and Women

iStock.com/PeopleImages
iStock.com/PeopleImages

Women often feel colder than men due to physical differences. Now, a new study shows that the two sexes have different biological processes underlying a specific kind of pain, too. As WIRED reports, research published in the journal Brain revealed that different cells and proteins were activated in men and women with neuropathic pain—a condition that is often chronic, with symptoms including a burning or shooting sensation. While scientists say further research is needed, these findings could potentially change the way we treat conditions involving chronic pain.

A team of Texas-based neurologists and neuroscientists looked for RNA expressions in the sensory neurons of spinal tumors that had been removed from eight women and 18 men. Some of the patients had pain as a result of nerve compression, while others had not experienced any chronic pain. While studying the neurons of women with pain, researchers noticed that protein-like molecules called neuropeptides, which modulate neurons, were highly activated. For the men, immune system cells called macrophages were most active.

"This represents the first direct human evidence that pain seems to be as sex-dependent in its underlying biology in humans as we have been suggesting for a while now, based on experiments in mice," Jeffrey Mogil, a professor of pain studies at Montreal's McGill University, who was not involved in the Brain study, tells WIRED.

So what exactly do these new findings mean for sufferers of chronic pain? Considering that clinical trials and drug manufacturers have traditionally failed to distinguish between the sexes when it comes to developing pain medication, the study could potentially form a foundation for sex-specific pain therapies that could prove more effective. This might be especially promising for women, who are more likely to have some condition that cause persistent pain, such as migraines or fibromyalgia.

"I think that 10 years from now, when I look back at how papers I've published have had an impact, this one will stick out," Dr. Ted Price, a neuroscience professor and one of the paper's authors, said in a statement. "I hope by then that we are designing clinical trials better considering sex as a biological variable, and that we understand how chronic pain is driven differently in men and women."

[h/t WIRED]

McDonald’s Is Testing Out Vegan McNuggets in Norway

McDonald's has never been an especially welcoming place for vegans (until 1990, even the fries contained meat). But now, the chain's Norwegian locations are working to change that. As Today reports, McDonald's restaurants in Norway have launched a vegan nugget alternative to the classic chicken McNugget.

The new vegan McNuggets are prepared to look like the menu item customers are familiar with. They're coated with a layer of breadcrumbs and fried until they're golden-brown and crispy. Instead of chicken meat, the nugget is filled with plant-based ingredients, including mashed potatoes, chickpeas, onions, corn, and carrots.

The vegan McNuggets are only available to customers in Norway for now, but if they're popular, they may spread to McDonald's in other parts of the world. Norway's McDonald's locations also include a Vegetarian McFeast burger on its menu.

McDonald's is famous for tailoring its menus to international markets, and vegetarian options are much easier to find in restaurants some parts of the world compared to others. In India, where one fifth of the population is vegetarian, customers can order the McAloo Tikki Burger, made from potatoes and peas, or a McVeggie sandwich.

[h/t Today]

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