Science Says You Shouldn’t Scratch Your Itchy Rash
When you’ve got an itch, your first instinct is to scratch it, bringing instant relief. However, any relief from scratching is short-lived. In fact, scratching can actually make the problem worse.
An itch can be triggered by an allergic reaction to allergens or irritants like poison ivy and certain metals, resulting in an itchy, swollen rash called allergic contact dermatitis.
If you give in to the urge to scratch, it will cause further inflammation that worsens symptoms and slows down the healing process.
Researchers from the University of Pittsburgh investigated how scratching leads to swelling and inflammation in mice to determine what drives the vicious cycle of itching and scratching.
“At first, these findings seemed to introduce a paradox: If scratching an itch is so bad for us, why does it feel so good?” said Daniel Kaplan, a professor of dermatology and immunology at the University of Pittsburgh.
“Scratching is often pleasurable, which suggests that, in order to have evolved, this behavior must provide some kind of benefit. Our study helps resolve this paradox by providing evidence that scratching also provides defense against bacterial skin infections.”
The research team used itch-inducing allergens to trigger eczema-like symptoms in the ears of normal mice and mice that lack an itch-sensing neuron.
When the normal mice were allowed to scratch, their ears got swollen and were filled with inflammatory immune cells called neutrophils.
In normal mice that could not scratch because they wore miniature collars similar to cones for dogs, as well as mice without the itch-sensing neuron, the inflammation and swelling were significantly milder.
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The experiment confirmed that scratching aggravates the skin further.
Next, the team showed how scratching causes pain-sensing neurons to unleash a compound known as substance P, which activates mast cells. Mast cells drive inflammation and itchiness via neutrophils.
“In response to scratching, the release of substance P activates mast cells through a second pathway, so the reason that scratching triggers more inflammation in the skin is because mast cells have been synergistically activated through two pathways,” Kaplan said.
Mast cells play a key role in various inflammatory skin conditions and allergic reactions, yet they also help defend against bacteria and other pathogens.
Given this dual role, the researchers wondered if activating mast cells through scratching would impact the skin’s microbiome.
In a series of experiments, the team demonstrated that scratching reduced the amount of Staphylococcus aureus on the skin.
It is the most common bacteria involved in skin infections. Scratching can be advantageous in some ways, but the damage it does to the skin probably outweighs the benefits.
Now, the researchers are looking into new therapies for dermatitis and other inflammatory skin conditions like rosacea and urticaria.
The study was published in Science.
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