Demi Moore endured prolonged stretches (from 6 to 9½ hours) of sitting still in a chair while a makeup team applied nightmare-inducing prosthetics to her face and body.

She and costar Margaret Qualley also devoted time to perfecting sexualized gyrations their celebrity fitness characters would perform in front of leering cameras and a slimeball of a boss, played by Dennis Quaid, and spent considerable time rehearsing how to brawl and attack each other (they’re good friends now, though).

Sounds like making the gruesome body-horror movie “The Substance” might have been one miserable experience.

Far from it, the actors say. They knew what they were getting into after reading the gonzo award-winning script from French director/screenwriter and provocateur Coralie Fargeat.

“It was an exciting script to come across and one that is as wild of a ride as watching the movie,” recalls Moore, star of countless films such as the beloved tearjerker “Ghost,” the iconic “St. Elmo’s Fire” as well as eyebrow raisers “Indecent Proposal,” with Robert Redford and Woody Harrelson, “Disclosure,” opposite Michael Douglas, and 1996’s critically panned “Striptease.”

In “The Substance,” Moore (seen of late stealing scenes in FX’s “Feud: Capote vs. the Swans”) plays fading L.A. fitness personality Elisabeth Sparkle, who resorts to a dubious regimen of injections that birth a younger variation of herself — Sue (Qualley) — from out of her spine. The two trade off weeks of going out in public or holing up in a near coma-like state in Sparkle’s sterile vast apartment. “The Substance” opens Friday in theaters and forcefully takes slugs at our  youth-obsessed culture and the male-fueled body expectations that undermine and wreak havoc on women.

Fading star Elisabeth Sprinkles (Demi Moore) contemplates a risky fountain-of-youth career gamble in “The Substance.” (Christine Tamalet/Universal Studios)

It’s 2024’s fiercest, most in-your-face satire, and one that placed huge demands on both actors, kicking them way out of any comfort zone.

“I think that’s why we both wanted to do it, “ said Qualley during a Zoom interview with Moore. “We are both people that love a challenge, love scaring ourselves, love pushing ourselves into uncharted territory. And to me, Demi’s had a whole career of doing that, from ‘G.I. Jane’ to ‘Striptease’ to ‘Ghost.’ There’s a new person every time.”

For Qualley — who co-starred in “Kinds of Kindness,” “Poor Things,” “Drive-Away Dolls” and the Netflix series “Maid” — landing the part of zealously ambitious Sue presented a new challenge.

“I’ve never played something so sexualized,” she said. “I’ve had the great privilege of not having to do that. And it was definitely scary to try on and I definitely needed to stretch.”

It helped that each star trusted the other, especially since, as Moore puts it, they were journeying into “uncharted territories.”

“And yes, there were questions to be answered and explored because of the depth of vulnerability for each of us in the different ways that it was demanding,” Moore adds. “Which is what made it so important that we were so united and so connected with one another. (It) really happened with great ease and grace from the first moment that we actually met.”

Qualley concurs.

“I was so lucky to have had Demi as my partner in crime in this process because first of all she’s as wise as they come. She’s seen it all. Second of all, she’s a girl’s girl and she’s just brave as hell.”

To Qualley’s point, Moore’s wisdom comes from decades of being in the Hollywood game and the glaring public spotlight. At times, she said, she placed an inordinate amount of attention onto how her body needed to meet others’ standards.

“I can say in my past when I was younger and much more insecure and I had a lot less certainty, that I placed a lot of meaning and value on my body being a certain way,” says Moore, 61. “And that if it wasn’t that way, (I) kind of put myself through a lot of hoops trying to live up to something. But what it gave me was an opportunity to surrender and let go and make being comfortable within myself my priority.”

“The Substance” boldly reflects the impossible, damaging body standards imposed on women, created by he male gaze, both agree. Those unrealistic demands lead to comparisons between women that can often be equally damaging, Moore said

“Ultimately, it’s the violence that we hold against ourselves,” she said. “What moved me in this story is that that is not even specific to women. It’s what we all do. It’s a human response of compare and despair where we’re measuring ourselves and it changes over time. But it’s that kind of pattern (where) we pick ourselves apart. And if you want to create a physical manifestation of that, what would it look like? In this case with Elizabeth, it’s actually that I deform.”

For a younger generation, though, there is a sense that more are abandoning the perfect body traps of the past, Qualley said.

“I’m actually pretty moved by the young generations,” the 29-year-old actor said. “I feel like there’s an open-mindedness and perspective that is so (expletive) fresh and cool, like we’re in continuous progress.”

“The Substance” reflects a specific mindset tied to the culture of the time, she adds.

“I think the movie we made is a reflection of something that someone endured during the ‘80s,” Qualley said. “I believe there’s hope. I believe we’re getting better, and that’s not to say it isn’t still hard out there. But I totally have faith in humanity and the generations to come.”

Even though “The Substance” is a tough watch that requires a strong stomach, its underlying message about the dangers of not accepting ourselves and the importance of coming together is important to hear — for all generations.

“Just that idea of being a rival between young and old and the messaging,” Moore said. “You’re one and to rival that is kind of a useless thing. When we come together we all rise up: As one.”