October 13, 2016 1:13 PM EDT

Hollywood hunk Zac Efron shared some experimental nail art on Instagram this week—but he wasn’t just messing around with polish colors. Efron, Chris and Liam Hemsworth, and other celebrities are participating in the annual Polished Man nail-painting campaign to combat child abuse. The challenge? Paint one nail (just one! sounds like a snap), post your photo, and donate to the cause to help raise awareness for the one in five children worldwide who are victims of violence, as the charity contends.

“Being a @PolishedMan isn’t just about remembering to buy flowers, how many rounds you shout, or how much you lift. It’s about saying no to violence against children,” Chris Hemsworth explained.

So far, two of the three Hemsworth brothers have taken on this latest social media challenge (the third brother, Westworld actor Luke, also participated last year). Zac Efron and famous surfer Kelly Slater have also joined in, and with tags out to celebrities like Robert Downey, Jr., Jimmy Fallon, and Tom Hiddleston, we expect to see plenty more unexpected manicures gracing our Instagram feeds in the near future. Nail polish: it’s not just pretty anymore.

Write to Raisa Bruner at raisa.bruner@time.com.

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