The pregnant singer looks beautiful in the photo dated 21 June, as she strikes a pose while applying some lipgloss.
"Happy first day of summer," she wrote. "Keep those lips hydrated!"
Christina's lip balm of choice is EOS Lip Spheres, £5.95, Cute Cosmetics. We first saw her gushing over the product back in May while hanging out backstage at The Voice US.
And she's not alone.
Kim Kardashian and Nicole Scherzinger are also big fans of the very cute round balms.
'Beautiful' singer Christina is expecting her second child; her first with fiancé Matthew Rutler. She's also mum to son Max from her marriage to ex-husband Jordan Bratman.
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