“I have to do a skin-care routine every single night,” says Billie Eilish. Midway through a world tour that sees her singing to packed stadiums, Eilish sticks to a routine both for the sake of her skin and her emotional self. “For me, I find a lot of peace in it and it brings me back down to myself; I feel like a person when I do it,” she says.  Fresh off the stage, she picks Josie Maran wipes as her makeup remover of choice, pulling her hair out of her face with a headband and hair tie. (Fun fact: the singer-songwriter does not have glam on tour, instead doing…