Scratch a cutaneous eruption that pica worsens and, now, a scientific team knows why, thanks to an investigation that describes how to rub the skin aggravates inflammation and swelling.
The study, led by scientists from the Pittsburgh University, has been done in a mouse model of a type of eczema called allergic contact dermatitis and the results are published in the Science magazine.
This condition is an allergic reaction to allergens or irritating skin – including poison ivy and certain metals such as nickel – that causes a pruriginous and inflamed eruption. Succumb to impulse, often irresistible, to scratch unleashes greater inflammation that worsens symptoms and slows cure.
In this study, researchers used itching inductive allergens to induce symptoms similar to those of the eczema in the ears of normal mice and those who do not stick because they lack a neuron sensor of itching, explains a statement from the American university .
When normal mice were allowed to scratch, Their ears swelled and filled with inflammatory immune cells called neutrophils.
On the other hand, inflammation and swelling were much milder in normal mice that could not scratch because they carried small Elizabethan necklaces -symptilated to the cones that are used in dogs -, and in the animals that lacked the sensor neuron of the itching.
This experiment confirmed that scratching the skin further aggravates, the researchers say.
THE KEY, IN THE MASTOCITOS
Next, scientists showed that scratch makes pain sensor neurons release a compound called substance P.
In turn, The P substance activates the mast cells -cells found in different tissues -which are key coordinators of inflammation that drives itching and inflammation through the recruitment of neutrophils.
In contact dermatitis, allergens directly activate mast cells, which causes small inflammation and itching, explains Daniel Kaplan.
But, in response to scratch, the liberation of substance P also acts the mast cells through a second route, so that the reason why scratch triggers more inflammation in the skin is because mast cells have been activated synergily through Two ways, adds the researcher.
Paradox
Kaplan acknowledges that scratching can be pleasant, suggesting that this behavior must cause some type of benefit. “Our study helps solve this paradox by providing evidence to scratch also provides defense against bacterial skin infections”.
Mastocies are the culprits of a series of inflammatory skin affections and allergic reactions, but they are also important for protection against bacteria and other pathogens.
Therefore, the researchers wondered if the activation of mast cells induced by scratch could affect cutaneous microbiome.
In experiments led by Marlies Meisel, The team showed that scratch reduced the amount of Staphylococcus aureus, the most common bacteria involved in skin infections.
“The finding that scratching improves defenses against Staphylococcus aureus suggests that it could be beneficial in some contexts,” says Kaplan, but “the damage that scratch produces on the skin probably compensate for this benefit when the itching is chronic.”
The team is investigating new dermatitis therapies and other inflammatory skin conditions, such as rosacea and hives, which suppress inflammation by addressing mast cell receptors.