What causes itchy skin? New research points to a previously unknown factor

Scientists are still trying to unravel the mystery of why skin conditions like eczema make it itchy.

One known cause is inflammation, which worsens as people scratch and their skin becomes damaged. But there may be another trigger, according to a study published Wednesday in the journal cell: a bacteria called Staphylococcus aureus.

Researchers at Harvard Medical School found that the bacteria can directly activate nerve cells in mice.

“The surprising thing is that in some cases where there was very little inflammation, we could still see the mice scratching. It turns out that the reason is that the bacteria acted directly on the nerve fibers that cause itching“explained one of the study’s co-authors, Isaac Chiu, associate professor of Immunology at Harvard Medical School.

A person with acute vesiculobular eczema shows blisters on their hands.BSIP / Universal Images Group via Getty Images

Before the study, scientists knew that S. aureus It was related to eczema, but the exact relationship was unclear. The new research found that once the S. aureus invades the skin of a mouse, releasing an enzyme called V8. This, in turn, activates a protein called PAR1, which is found in nerve cells in the skin. The activated protein sends a signal to the brain that makes the mouse feel itchy and start scratching.

Laboratory experiments with human nerve cells showed that the same mechanism is possible in people, but researchers are not yet sure whether the results can be translated literally.

The most common type, Atopic dermatitis causes chronic itching and dryness and cracking of the skinand is closely related to allergies such as asthma or hay fever.

Still, the research may offer scientists a new direction in developing treatments to combat eczema, which affects about 10% of the U.S. population. The most common type, atopic dermatitis, causes chronic itching, leaves the skin dry and cracked, and is associated with allergies.

“Almost all lesions in patients with atopic dermatitis have “Staph aureus”said Liwen Deng, another co-author of the study and a postdoctoral researcher in Chiu’s lab.

In the study, mice were exposed to the bacteria S. aureus directly on the skin for several days. The researchers found that on the third day, the animals had skin irritation and, on the fifth day, they scratched much more than mice that had not been exposed.

Affected mice were also more likely to develop alloknesis, a disorder in which people become itchy when exposed to events that do not normally cause itching, such as a gentle touch.

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To rule out the possibility that inflammation could still cause itching, the research also included mice with lower levels of immune cells and inflammatory chemicals associated with skin allergies. The results still suggested that the bacteria was causing the itching.

“The study was able to separate the inflammatory response from the itch response,” said Nathan Archer, associate professor of dermatology at Johns Hopkins University School of Medicine, who was not involved in the research.

Dr. Peter Lio, director and founder of the Chicago Integrative Eczema Center, said in an email that the Harvard study “strengthens and expands our understanding” of the role staph bacteria play in itchy sensations.

“We’ve learned about the many toxins that staphylococcus carries: some drive inflammation, others damage the skin barrier, and others directly cause itching,” said Lio, who was also not involved in the research.

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According to Archer, the study Could offer important clues about how to treat eczema patients that do not respond to available treatments. Doctors often prescribe topical steroids. In 2017, an injection was approved for adults with moderate or severe eczema.

Deng said, “Right now there are really no targeted treatments to combat the bacteria.”

In the future, he said, scientists could develop a topical treatment that blocks the pathway. S. aureus that causes the itching. Another option would be to repurpose an anticoagulant drug called Vorapaxar to treat eczema, since it is the only FDA-approved drug that blocks the PAR1 protein.

In the new study, Vorapaxar appeared to reduce the desire to scratch in the mice that received it.

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Chiu noted that the investigation It could even have applications for skin conditions other than eczemalike impetigo, a disease that causes red sores on the faces of babies and children.

“Any situation where staphylococci aureus may be present on the skin could be relevant to our findings,” he said.