A groundbreaking study published in the journal Science has revealed that scratching, a behavior often associated with discomfort, may have an evolutionary advantage. Conducted on mice, the research indicates that a certain amount of scratching could serve a beneficial purpose, particularly in combating skin infections. The study was published on January 30 and offers new insights into the complex relationship between itch sensation and skin health.
The research team, led by experts in immunology and neurobiology, focused on how scratching impacts the presence of Staphylococcus aureus, a common bacteria found on the skin. In a controlled experiment, the researchers exposed the ears of mice to an itch-inducing substance followed by the bacteria. Remarkably, mice that had their itch-sensing neurons deactivated exhibited ten times fewer S. aureus bacteria on their skin after just one day. This finding suggests that scratching might play a role in enhancing the skin's defense mechanisms.
Skyler Ware, a freelance science journalist with a Ph.D. in chemistry from Caltech and a former AAAS Mass Media Science and Engineering Fellow at Science News, underscores the significance of this study. The research not only sheds light on why organisms feel the urge to scratch but also proposes that this behavior may be an evolutionarily conserved response seen across various species.
To test their hypothesis, the researchers bred mice with specific itch-sensing neurons deactivated. This strategic approach allowed them to observe the impact of scratching on bacterial levels directly. Liwen Deng, an immunologist at Harvard Medical School who was not involved in the study, noted the wide prevalence of scratching across the animal kingdom. “It’s highly evolutionarily conserved,” Deng stated. “But it just seems so damaging, and we really had no understanding of what could be helpful about it. So it really is one of the first studies to show that it could be a beneficial response.”
Dr. Daniel Kaplan, a co-author of the study, echoed these sentiments, emphasizing the paradox of scratching’s dual nature. "Scratching is often pleasurable, which suggests that, in order to have evolved, this behavior must provide some kind of benefit," he explained. He further elaborated on the findings, saying, "The finding that scratching improves defense against Staphylococcus aureus suggests that it could be beneficial in some contexts. But the damage that scratching does to the skin probably outweighs this benefit when itching is chronic."
This study represents a significant advancement in understanding the biological underpinnings of itch and scratch behavior. While scratching has often been considered harmful due to its potential to damage skin and introduce infections, this research highlights its potentially protective role against certain pathogens.
