Have you ever wondered why yawns are contagious? Why bubble wrap is so fun to pop? And how is it that Justin Bieber's face can immediately make people dry heave and go into shock? So many of life's important questions go unanswered.
But, well, a recent study using mice has unraveled one of life's more low-level, yet curious, mysteries: what is an itch and why do we scratch? Gizmodo reports that the act of scratching is actually a defense mechanism that protects our skin from "objects in the environment or nasty insects and parasites." When we scrape across our skin with our fingernails, we try to kill whatever's disrupting our vibe. What causes the itch, though, is a molecule found in the heart, called the natriuretic polypeptide b, (Nppb) which sends a message to our spinal cords when something is irritating or dangerous enough to warrant a physical response.
"Itching itself likely evolved to protect us from disease," says Mark Hoon, a molecular geneticist at the National Institute of Dental and Craniofacial Research in Bethesda, Maryland. Consider this: a killer mosquito is on your arm, moments away from infecting you with malaria -- just when their little prick hits your skin, the Nppb cells send a message to the brain commanding you to scratch yourself. The mosquito is dead and you can live your life without the joy of malaria.
HowStuffWorks further explains how scratching puts an end to the feeling of itchiness after the culprit is gone: "When your brain realizes that you've scratched away the irritant, the signal being sent to your brain that you have an itch is interrupted and therefore no longer recognized by the brain." That's why you don't scratch all the way through your skin. Ew.
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Jeremy Glass is a writer for Thrillist and is coincidentally super itchy from writing this.