Michelle Monaghan Reveals the Weekly Beauty Treatment That Turned Her into The White Lotus’ Jaclyn (Exclusive)

The actress, who stars in U Beauty’s latest campaign, tells PEOPLE about her rigorous self-tanning routine

Michelle Monaghan was committed to her role in The White Lotus.

At a recent New York City event celebrating her as U Beauty’s first-ever brand ambassador, the actress, 48, shared the methodical beauty routine she implemented for her character Jaclyn. On season 3 of the hit HBO series, Monaghan plays a TV star on a girls’ trip at The White Lotus resort in Thailand.

In order to maintain Jaclyn’s tropical, effortlessly glam look throughout months of shooting, the actress self-tanned weekly.

“I committed to it every Sunday,” she tells PEOPLE. “So everybody’s like, ‘We’re going to go down to the beach and for a swim.’ And I was like, ‘I can’t do it.’ Instead, I was putting on the self-tanner and waiting for it to dry for six or seven hours because it was so humid.”

She continues, “And it became this ongoing joke that they just knew. They’re like, ‘Oh, don’t bother asking Michelle. She’s doing her tan.'”

Monaghan adds that the tanning process helped her to get into character.

“But once I put that tan on and then that blonde hair and I felt like I was inhabiting a very specific character,” she explains. “And then she wore a very bright pink coral-y nail polish that we would have to do once every week or two.”

“I loved being blonde so much and I was nervous because I am a brunette,” she says her blonde hair transformation on the show. “I knew that [series creator] Mike [White] really wanted me to be blonde. And I was like, ‘Of course I’ll do whatever you want.’ But I was worried because I knew that I was going to have to go back to being brunette for a film afterwards.”

Like her tan, Monaghan’s blonde locks required rigorous maintenance. So, celebrity colorist Tracey Cunningham took several trips to Thailand, where the season was filmed, to keep Monaghan’s color in tip-top shape during shooting.

The White Lotus season 3 also stars Aimee Lou Wood, Patrick Schwarzenegger, Jason Isaacs, Leslie Bibb and Walton Goggins, as well Natasha Rothwell, who is reprising her season 1 role as spa manager Belinda Lindsey.