Actresses Get Naked After 40

July 21, 2009— -- Sandra Bullock waited until she was 44. Diane Keaton was nearly 60.

Both actresses bared all on the big screen at an age when most women are doing their best to cover up their bodies.

Bullock had tongues wagging over her first nude scene in the new film "The Proposal," which debuted July 10 at the top of the box office.

"Box office like this, I'm going to be naked in every film," she joked on a British morning show.

Known for playing prim characters in films such as "Miss Congeniality" in 2000, Bullock is the latest actress older than 40 to jump on the nude bandwagon. Mary-Louise Parker, Marisa Tomei and Kathy Bates all waited until after 40 to shed their clothes on screen.

The reasons vary.

"They may need the money or need the work," Jeanine Basinger, the film studies chairwoman at Wesleyan University in Middletown, Conn., told ABCNews.com. "If you're a working actress of a certain age, you have to make a living.

"A lot of them say it's the part," she added. "In Bullock's case, that scene is a major comedy moment."

UCLA film professor Vivian Sobchack said, "It's also a way of reinventing oneself and reviving a career. It's an assertion of I'm still viable, I'm still here damn it, I'm still erotic and I still have sex appeal."

Whatever the case, the way today's actresses older than 40 look on screen and the way audiences look at them are a lot different from decades past.

"There is a larger phenomenon, in which 50 is the new 30," Sobchack said. "Within the context of our make-yourself-over culture, there is a very different attitude toward the notion of older women, particularly. No longer are they merely disgusting, or your mother.

"It used to be women at a certain point, over a certain age, were seen primarily as mothers or grandmothers -- certainly benign or bitchy, but really not sexual," she added. "That's why Mrs. Robinson was considered so sexual way back."

When actress Anne Bancroft, at 36, played the older Mrs. Robinson who seduces a younger man, played by Dustin Hoffman, in 1967's "The Graduate," she was seen as almost too sexy. She didn't work again for the next five years.