Scratching an itch can increase eczema and skin irritation, research shows

Understanding the Itch: Research on Scratching and Inflammation

Dealing with a bug bite or a rash? The urge to scratch can be strong, but researchers have found that this instinct might actually lead to more discomfort in the long run. Scratching might feel good momentarily, yet it likely prolongs the sensation, according to recent studies.

Scratching is a natural reaction to skin irritants, but it can also amplify inflammation and worsen conditions like eczema. Despite this, the reasons behind why scratching leads to increased swelling—and any potential benefits from this behavior—remain somewhat unclear.

A team from the University of Pittsburgh, led by dermatology and immunology professor Daniel H. Kaplan, set out to explore the connection between itchiness, scratching, and inflammation. To do this, they triggered allergic contact dermatitis in mice by applying an allergen to their ears, mirroring skin reactions that humans might experience from poison ivy, nickel, or certain skin products.

The experiment featured two groups of mice: one with normal itch-sensing neurons and the other genetically altered to lack these neurons. Some mice were free to scratch, while others were kept from doing so with collars reminiscent of the “cone of shame” often used for pets.

The study revealed that scratching activated mast cells, which play a crucial role in the body’s immune response. These cells release histamine and other inflammatory substances that contribute to the sensation of itching. Interestingly, while it’s gratifying to scratch, allowing it freely led to an increase in substance P—signaling that promoted further mast cell activation and thus heightened inflammation.

Mice that were prevented from scratching exhibited less inflammation, suggesting that restraint can be beneficial in managing itch-related skin responses.

While scratching may have evolved as a protective measure—perhaps beneficial for warding off bacteria—Kaplan noted that the overall damage it can cause often outweighs those advantages, especially when itchiness becomes chronic. In another part of their study, the researchers found that scratching reduced levels of Staphylococcus aureus, a bacterium linked to skin infections. However, the harm inflicted by scratching might overshadow this seemingly positive effect.

This leads to a curious question: if scratching feels so good, why is it detrimental? The pleasurable sensation of scratching might suggest an evolutionary advantage, which this research aims to unpack. Ultimately, it appears that the practice may offer some defense against bacterial infections, but the risks of heightened inflammation remain significant.

For those looking for relief, the American Academy of Dermatology suggests using cold compresses or applying 1% hydrocortisone cream to alleviate itching.