Who knew that just a few years later, makeup-free photos would become a celebrity trend?

Female stars have been rushing to publish photos of themselves without makeup. Last week, Rihanna, known for her brightly colored hair and makeup, posted a photo of herself on Twitter looking like the girl next door, makeup free and with braided pigtails. That followed a quadriptych of photos she posted several months ago, showing her looking as if she had just rolled out of bed, albeit with flawless and radiant skin.

Also last week, Nicole Polizzi, the “Jersey Shore” star better known as Snooki, posted a photo of herself without any of the heavy bronzer, eyeliner and pink blush that she is known for. She looked like someone you could bring home to meet Mom. “My clean canvas before I get artistic,” the Twitter message read.

They were not the first: Jennifer Love Hewitt, Demi Lovato, Lady Gaga and others have all self-published photos without makeup in recent months.

And it’s not just young starlets and pop idols. The comedian Roseanne Barr, under the Twitter handle @TheRealRoseanne, posted a photo of herself in bed without makeup, her chin drawn back into the folds of her neck.

Are the photos a humble gesture or a publicity stunt?

“When a celebrity posts a picture of herself without makeup, she knows that it will generate great P.R.,” said Emilie Zaslow, an assistant professor of communication studies at Pace University in New York, who studies beauty in consumer culture.

The photos, she added, are a way for a celebrity to prove “that she doesn’t need the makeup she typically wears” and for people to “imagine the celebrity as down to earth, authentic and intimate with her fans.”

That may explain the photo that Kim Kardashian posted of herself on Twitter in February. “Sweatpants hair tie chillin with no make up on,” Ms. Kardashian wrote. The photo was taken in a marble-lined bathroom, where she looks decidedly unglamorous but still showing plenty of skin in gray sweat pants and a black sports bra. She is seen staring into her smartphone as she frames the photo with her left hand.

The tabloid media reacted with oohs and aahs, rewarding Ms. Kardashian with ample attention and praise. “Kim Kardashian flaunts curves,” The Daily News in New York wrote in a headline. The Daily Mail in England said, “When it comes to relaxing, Kim Kardashian still manages to look as sexy as ever,” adding that she looked “picture perfect” and making note of her “washboard stomach.”

In a few cases, celebrities seem to be going out on a limb. In May, the actress AnnaLynne McCord posted an unvarnished photo of herself, her face dotted with red blemishes.

“I woke up this morning and decided I’m over Hollywood’s perfection requirement,” Ms. McCord wrote in a Twitter message accompanying the photo. “To all my girls (and boys) who have ever been embarrassed by their skin! I salute you! I’m not perfect — and that’s okay with me!”

In most cases, the photos are a bid for attention — even unconsciously, said Soroya Bacchus, a Los Angeles psychiatrist who treats several celebrity patients.

“It really goes to some underlying sense of narcissism that comes across as ‘Oh, look at how humble I am,’ ” she said. “It’s a false sense of humility.”