There’s a Reason Why Nails on a Chalkboard are so Unbearable

Merely imagining the sound of nails screeching across a chalkboard is enough to make some people shudder. There aren’t many other ear-piercing sounds that live up to the notoriety of nails on a chalkboard. So what is it about this specific noise that makes it so intolerable? It turns out its effects are both psychological and physiological, and humans are actually predisposed to despise the sound.

While it might seem logical that the most distressing sound frequencies would be the highest and lowest ones, that’s actually not the case. According to study researcher Michael Oehler, professor of media and music management at the University of Cologne in Germany, the human ear is most sensitive to sounds that fall within the range of 2,000 to 4,000 Hz (hertz). Along with nails on a chalkboard, other sounds in this frequency range include crying babies and various acoustic features of human speech.

Oehler and colleagues speculate that these findings may suggest that the shape of our ear canals evolved to amplify certain frequencies involving human communication — perhaps this explains why some mothers instantly leap out of bed when their baby starts wailing in the middle of the night. Unluckily for us, since the sound of nails on a chalkboard falls within that sound range, it too becomes amplified.

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Even though we’re predisposed to react sharply to such sounds, the study also found psychological factors reinforce our deep hatred for nails on a chalkboard. The researchers told half of the study participants what the sounds really were, but told the other half that they were clips from contemporary music. Those who thought they were listening to strange modern jams rated the sounds as more pleasant. However, they too showed significant changes in electrical skin conductivity, a physical response to stress.

While our adverse reactions to the sound of fingernails scraping a chalkboard are certainly physical, we’ve also been conditioned to loathe the noise through popular opinion and films with hair-raising scenes of teachers taking extreme disciplinary measures.

But no matter whether evolution or society is to blame, the sentiment toward the despicable sound is one thing almost all humans can genuinely agree upon.