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New research published in the journal Science Discover how scratching aggravates inflammation and swelling in a mouse model of a type of eczema called allergic contact dermatitis.
“At the beginning, these results seemed to introduce a paradox: if scratching a itching is bad for us, why does it feel so well?” The said principal author Daniel Kaplan, MD, Ph.D., professor of dermatology and immunology at the University of Pittsburgh.
“The scratches are often pleasant, which suggests that, for having evolved, this behavior must provide a kind of advantage. Our study helps to resolve this paradox by providing evidence that striking also provides defense against bacterial skin infections. “”
Allergic contact dermatitis is an allergic reaction to allergens or skin irritants, including poison ivy and certain metals such as nickel – itching a rash that itching and swollen. Succombing often irresistible to scratch triggers additional inflammation that worsens symptoms and slows healing.
To understand what motivates this vicious circle, Kaplan, the first author Andrew Liu, student of the training program for medical scientists of Pitt, and their team used allergens inducing itching to induce symptoms of the eczema type on the mice of the mice normal and those who do not get it itching because they do not have a detection neuron of itching.
When normal mice have been allowed to scratch, their ears have become swollen and filled with inflammatory immune cells called neutrophils. On the other hand, inflammation and swelling were much softer in normal mice which could not scratch because they wore tiny Elisabethains necklaces, similar to a cone that a dog could display after a visit to the veterinarian, and In animals that lacked the itch detection neuron. This experience has confirmed that scratching more aggravates the skin.
Then, the researchers showed that scratching causes the release of pain neurons to pain to a compound called substance P., in turn, the substance of the mastocytes, which are key coordinators of inflammation that cause Itching and inflammation via the recruitment of neutrophils.
“In contact dermatitis, mastocytes are directly activated by allergens, which leads to inflammation and minor itching,” said Kaplan.
“In response to scratches, the release of the substance P activates mastocytes through a second path, so that the reason why scratching triggers more inflammation in the skin is that mast cells have been activated in synergy by two ways . “
Mastocytes are culprits in a range of inflammatory skin conditions and allergic reactions, but they are also important to protect against bacteria and other pathogens. As such, researchers wondered if the activation induced by the scrambles of mastocytes could affect the skin microbiome.
In experiences led by co-author Marlies Meisel, Ph.D., assistant professor of immunology in Pitt, the team showed that stripes reduce the quantity of staphylococcus aureus, the most common bacteria involved in skin infections , on the skin.
“The conclusion that scratching improves defense against Staphylococcus Aureus suggests that this could be beneficial in certain contexts,” said Kaplan. “But the damage that scratching does to the skin probably prevails over this advantage when itching is chronic.”
Now, researchers are studying new therapies for dermatitis and other inflammatory skin conditions such as rosacea and hives which suppress inflammation by targeting receptors on mastocytes.
More information:
Andrew W. Liu et al, Scratching promotes allergic inflammation and the defense of the host via the activation of neurogenic mastocytes, Science (2025). DOI: 10.1126 / Science.Adn9390. www.science.org/doi/10.1126/science.adn9390
Supplied by the University of Pittsburgh
Quote: A new study explains why you should not scratch a rash for itching (2025, January 30) recovered on January 30, 2025 from https://medicalxpress.com/news/2025-01-shouldnt-itchy-rash.html
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