‘America’s Smutty Sweetheart.”

“Lurid Meg Ryan heats up a kinky potboiler”

“Meg Strips Down.”

Those were a few of the newspaper headlines that greeted Meg Ryan’s new film, “In the Cut.” It had been more than a decade since Ryan had taken off her clothes in “The Doors” — and in the intervening years, she reportedly had “no-nudity” clauses written into her contracts. But now here she is in a sexually explicit movie with full-frontal nudity.

The consensus among critics as to why Ryan decided to take it all off? Not because she wanted to show off her fabulous-at-41 body. Not because she thought a little titillation would boost her box-office currency. (It has, after all, been five years since her most recent $100 million hit, “You’ve Got Mail.”)

Ryan, they argued, wanted viewers to take her more seriously. Whether this is actually true hardly matters. (In interviews, Ryan claimed she simply liked the script and was looking for a new challenge.) The point is that our culture’s perceptions about onscreen nudity have drastically changed.

Nude scenes are no longer the means for a B-list starlet to grab attention before her star fades for good; they’re no longer what a young actress is forced to do before she makes it big and starts demanding those “no-nudity” contract clauses.

Nudity — and, often, explicit sex scenes — are what you do if you want to go gunning for a prime spot on the A-list. If you want to be looked upon as a real actress.

Never before have virtually all of the major female performances in a given year contained so much nudity. Nicole Kidman reportedly demanded that the love scenes in “The Human Stain” be reshot and made even racier. Kidman’s fellow Oscar-winners Gwyneth Paltrow and Jennifer Connelly get naked in, respectively, the recent “Sylvia” and the upcoming “House of Sand and Fog.” You can see pretty much all of Naomi Watts in the upcoming “21 Grams,” playing a woman whose husband and daughters are killed — it’s a performance widely expected to be an Oscar front-runner this year.

Never before have we seen so many top actresses so matter-of-factly go as far as they are going. Ryan’s sex scenes in “In the Cut” had to be cut to secure an R rating (a seven-minute-longer version will reportedly be released in Europe). Meanwhile, “The Brown Bunny” — director/actor Vincent Gallo’s mostly plotless portrait of a guy driving around and pining for his lost lover — became a “cause celebre” on this year’s festival circuit because of an explicit scene in which Oscar nominee Chloe Sevigny (“Boys Don’t Cry)” performs oral sex on Gallo.

Serious actresses earning the industry’s respect by playing up their sexuality is certainly nothing new — Jane Fonda won an Oscar in 1972 for playing a call girl in “Klute.” But performances such as Fonda’s used to be an exception — now they’re becoming the no-big-deal rule. It’s a marked shift, too, from the past decade or so of onscreen nudity — where actresses stripping down (Sharon Stone uncrossing her legs in “Basic Instinct” or Demi Moore swinging on a pole in “Striptease”) was all about titillation and selling the movie.

When — and why — did this shift occur? Three actresses probably deserve much of the credit: Connelly, Julianne Moore and Halle Berry.

Moore’s infamous nude scene in “Short Cuts” (1993) — an angry fight with her husband (Matthew Modine) while she isn’t wearing any pants — remains one of the most debated in recent movie history. You can feel (as I do) that it’s contrived and exploitative, or you can feel (as director Robert Altman wants you to) that it’s an honest, intimate portrait of the way married people actually live and argue. Either way, there’s no denying the scene got people’s attention and led to another sexually explicit part for Moore, as the porn star in “Boogie Nights” (1997), which earned her first Oscar nomination.

Director Ron Howard has repeatedly said that he never would have considered Connelly for her Oscar-winning part in “A Beautiful Mind” until he saw “Requiem for a Dream” (2000) — Darren Aronofsky’s grim indie drug-addiction drama that ends with Connelly at a sex party.

Most moviegoers and critics used to regard Berry as not much more than a pretty face with the canny ability to exploit her body (witness her reported $1 million bonus for going topless in 2001’s “Swordfish”). But then she got naked again for a raw, lengthy, emotionally draining sex scene in “Monster’s Ball” — and a few months later she was holding an Oscar.

The message to other movie actresses is obvious: The more naked and unstrung you are, the more seriously you will be taken. It’s a message that was cemented last year, when Diane Lane reinvented her career (and got an Oscar nomination) for “Unfaithful.”

That’s not to suggest that the motivations of these actresses are purely cynical. Quite the opposite: This trend is indicative of a larger one in our culture — an eagerness to treat sex seriously and provocatively.

In recent years, we’ve seen a number of films from Europe — among them, Catherine Breillat’s “Romance” and Gaspar Noe’s “Irreversible” — that incorporate pornographic elements into traditional narratives. These artists are attempting to bring verisimilitude to the sex scene — usually the most fake-seeming aspect of a film. And slowly we’re seeing that influence trickle into mainstream American filmmaking.

To be certain, this trend introduces all sorts of problems. We’re probably seeing more men than ever before getting just as naked as the women — including Sean Penn in “21 Grams,” Ewan McGregor in “Young Adam,” due early next year, and Mark Ruffalo in “In the Cut.” But no one’s buzzing about how these guys are especially brave; as a culture, we still equate male nudity with virility, not vulnerability.

“The Human Stain,” “Sylvia” and “In the Cut” haven’t made much of a ripple at the box office — a further testament to how matter-of-fact nudity is treated these days. But it’s also a testament to how unrelentingly grim and dour these movies are.

For these actresses, sex must still be equated with tragedy, failure and self-destruction for the role to have artistic credibility. (In “In the Cut,” the women who enjoy sex the most end up with their heads chopped off — and this from a movie directed by a woman.) There are the occasional exceptions when actresses have been able to exult in sexual fantasies: Kate Winslet in “Holy Smoke,” Lane in the first hour of “Unfaithful.”

But the question remains: Will women onscreen ever get to be completely sexy, joyful and in charge, with little in the way of negative repercussion?

Now, that would be shocking.