Margot Robbie and America Ferrera‘s skin was practically glowing in Barbie, and throughout the press tour – and there was a secret ingredient to getting it that way.

Skin health specialist and facialist Jasmina Vico spoke to Vogue about the secret to their skin, and jokingly called it a “witch’s brew” type of tea.

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“It’s Barbie and she needs to look perfect, so the brief for the skin was to create that halo of light often seen in 1940s photographs,” she told the magazine.

Jasmina added that “everything in the movies is about lighting. That’s when I thought, okay, we’re going to work on the liver; calm the nervous system; and make skin glow, but crucially, we’re going to work on that glow from within.”

The tea that she chose for not just Margot and America, but for the entire cast, was milk thistle tea, which was brought to the Barbie sleepover.

“Milk thistle cleanses your liver,” she shared. “When that happens, our liver automatically produces more glutathione, which then makes the skin more radiant. One of the most important ingredients within it is silymarin, which is now featured a lot in skincare formulas.”

Jasmina also shared a tip with the tea, saying it needs to be brewed for 20 minutes so its bitter.

“The liver likes anything bitter, because it helps it to flush,” she says, adding that “this tea is like a witch’s brew!”

On top of the tea, Jasmina also developed skin care routines for many of the cast, with a lot of focus on Margot.

“I looked after her like a baby!” she joked. “Not just her skin, but her energy. It’s a stressful job so we worked on calming her and making her feel great.”

Barbie is still in theaters, pushing to be the next $1 billion movie. Find out if a sequel is planned yet.