A new study published in the journal Science suggests that scratching an itch may have an evolutionary benefit. Researchers bred mice with certain itch-sensing neurons deactivated and found that they developed less inflammation and a lower risk of infection when scratched. The findings indicate that scratching boosts the immune response at an itchy injury site, helping to ward off infection.
The study’s lead author, Dr. Daniel Kaplan, notes that if scratching is bad for us, it must provide some kind of benefit. To test this hypothesis, researchers dabbed allergens on mice’s ears to trigger an itchy sensation and compared the allergic reactions in modified mice to those in normal mice wearing collars that prevented them from scratching.
The results showed that scratching triggered inflammation due to pain-sensing neurons releasing a substance that activates “mast cells,” which act like alarms in the immune system. However, the mice with cones developed much less swelling, suggesting that scratching was responsible for most of this inflammatory response.
When exposed to an itch-inducing substance and Staphylococcus aureus bacteria, normal mice without collars had 10 times fewer bacteria on their skin compared to those with collars and those without itch-sensing neurons. This suggests that scratching boosts the immune system’s defenses against infection.
While the study suggests that scratching may have some benefits, it also notes that excessive scratching can worsen chronic conditions and slow down healing processes. The findings provide new insight into why humans itch in the first place, highlighting the importance of finding a balance between beneficial and damaging behaviors.
Source: https://www.livescience.com/health/its-tough-to-resist-scratching-an-itch-and-evolution-may-be-to-blame