Here’s What Can Cause Itchiness, According to New Research

Scientists discovered a connection between a bacteria linked to eczema and an itch-causing enzyme in a study of mice

A woman itches her arm
Eczema affects almost 32 million people in the United States. Viktor Cvetkovic via Getty Images

At some point in your life, you’ve probably experienced the irritating sensation of itchy skin. Maybe you’re one of the 31.6 million people in the United States who have the incurable and inflammatory skin disease known as eczema. But the urge to scratch can be more than just annoying—itching can weaken our skin and expose our bodies to outside elements. 

Researchers have long known that people with conditions like eczema tend to have higher prevalence of a bacterium called Staphylococcus aureus on their skin, but its exact link to itchiness was unclear. Now, in a study of mice and human samples, a team of scientists has found that S. aureus releases an enzyme called V8 protease onto the skin, which helps activate itch-driving neurons. They published their results in November in the journal Cell

“Whilst we have previously recognized that staph aureus plays an important role in eczema, its contribution to itch has not previously been recognized,” Emma Wedgeworth, a consultant dermatologist and British Skin Foundation spokesperson who was not involved with the study, tells the Guardian’s Nicola Davis. “Hopefully, this understanding will translate into new treatment options helping to tackle the misery of itch and eczema.”

To glean more information into the mechanism behind itch, researchers applied methicillin-resistant Staphylococcus aureus (MRSA) onto the skin of laboratory mice and monitored the results over several days. They found that the exposed mice had higher skin damage and itchiness compared to mice that were not exposed to the bacteria. 

Next, the team focused their attention on ten enzymes that S. aureus releases upon skin contact to see whether they could identify which was responsible for causing itchiness. Using several modified versions of S. aureus that lacked different portions of the microbe’s genetic makeup, the team used the process of elimination to dismiss nine of the enzymes, leaving protease V8 as the culprit. Skin samples taken from humans with a form of eczema called atopic dermatitis confirmed that these patients had more of S. aureus and higher V8 levels than people without the condition. 

The researchers discovered V8 creates itch by activating a protein called PAR1, which is located on sensory neurons and involved in blood clotting. After the team treated the mice with a drug to block PAR1, the rodents were no longer as itchy. Coincidentally, this PAR1 blocker, called Vorapaxar, is already an approved medication to treat blood clots in humans, so it could be repurposed to treat eczema, per a statement from Harvard Medical School. 

“We just got lucky that that was already an FDA-approved compound,” Liwen Deng, a researcher at Harvard Medical School and lead author of the paper, tells NPR’s Nell Greenfieldboyce. “We treated them orally with the drug, and it completely blocked the itching and scratching that we normally observe when we apply bacteria to mice.”

The researchers still aren’t sure of the exact purpose behind S. aureus’s itch-causing tendency. It might be that scratching helps the microbe spread to new areas or that it damages the skin, allowing the bacteria to more easily establish itself.

“We’re not actually sure why Staphylococcus aureus would want to be inducing an itching response and whether it’s beneficial for the microbe,” Deng tells NPR. “We’re really interested in testing that.”

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