Natalie Portman, Cate Blanchett and Sabrina Carpenter all use the same lip balm. SplashNews/ Getty/ Shutterstock You don’t have to travel Down Under to score stars’ secret to soft lips. While many celeb skin care routines are high-end, it turns out A-listers have been gatekeeping an under-$10 Australian drugstore staple for years. Lucas’ Papaw Ointment — the iconic red tube seen in plenty of celebrity makeup artists’ stashes — is the multipurpose balm behind the hydrated pouts of stars like Sabrina Carpenter, Cate Blanchett and Natalie Portman. (It’s even rumored that Meryl Streep’s longtime MUA uses it on “The Devil Wears Prada” icon, but his lips are sealed.) Lucas Papaw Ointment Lucas Papaw contains fermented papaya and was originally made over 100 years ago as a general-purpose treatment for dry or irritated skin. Its long history in Hollywood first started 25 years ago, when makeup artists started using it to tame eyebrows and give lips a shiny look on TV and film sets.…