LOS ANGELES: The storm over Renee Zellweger's new-look face has thrown the spotlight on one of Hollywood's eternal questions: How do you grow old in Tinseltown?

The Bridget Jones star, who won a Best Supporting Actress Oscar in 2004 for Cold Mountain,”appeared unrecognisable at a women in Hollywood awards show earlier this week.

Gone were the sulky pout and rounded cheeks from her turn as the eternal singleton Jones in the 2000 and 2004 movies, replaced by the 45-year-old's impressively wrinkle-free and slimline face.

She became an instant water-cooler and Twitter trending topic, with endless comments about what plastic surgery or botox she has had done, while others worried about her health.

Some denounced Hollywood itself for the pressure it imposes on actresses to meet traditional ideals of beauty.

“In Hollywood it's strange not to (have plastic surgery) if you are a woman. You can't get work. Movie casting directors won't hire you if you look old,” said Sasha Stone, founder of www.awardsdaily.com.

It is a Tinseltown taboo, not to be allowed to age naturally, in contrast to places like Britain and France, Stone told AFP.

“It's an American phenomenon, an American obsession,” she said.

There is a long list of actresses who have gone under the knife to maintain their youthful appearance: Demi Moore, Nicole Kidman, Meg Ryan, Jane Fonda and Melanie Griffith to name but a few.

Some have gone a little too far in this pact with the devil, finding themselves with slightly over-rounded cheeks or “trout lips,” with a little too much padding around the mouth.

“When they do their face, they hope to keep getting the A-list parts. They don't want to play grandmothers. They want the leading roles,” said Stone.

Eternal youth

The ideal they are striving for is embodied for example by Jennifer Lawrence, the Hunger Games star who won an Oscar at the tender age of 22 last year for Silver Linings Playbook. The obsession with youth is less strong for men, who continue to win leading roles into their older years, including romantic and action parts. Mickey Rourke's and John Travolta's cosmetic surgery is more the exception than the norm.

In 2013, there were about seven million cosmetic surgery operations on women in the US aged 40-54. Botox injections and eyelid reconstruction were the most popular.

Plastic surgeon Ashkan Ghavami, whose Beverly Hills office sees many celebrities, said modern technology only adds to the pressure on actors and actresses.

“Right now we have high definition movies and TV shows where they show you the make-up and the wrinkles. So there's a lot more pressure on people to look good in real life,” he said.

In his view, Zellweger's surgery wasn't a success because her eyelids are too stretched and she has too much botox.

The actress, who has not confirmed she had work done on her face, called the storm triggered by her latest look "silly".

“I'm glad folks think I look different! I'm living a different, happy, more fulfilling life, and I'm thrilled that perhaps it shows,” Zellweger told People magazine.

Tom Nunan, a professor at the UCLA School of Theatre, Film and Television, said it was “sad” that a star as big as Zellweger can't admit to her personal choices publicly.

“Everybody understands a little botox here and there, a little eye lift, “he said.