When actors sign on a film, they're signing on to much more than just acting. Sometimes their appearances undergo a drastic change.

In the case of Hollywood actress Cameron Diaz, she lopped off her gorgeous hair to play the mother of a cancer-stricken child in the movie My Sister's Keeper, which hits theatres this Friday.

Diaz plays Sarah Fiztgerald whose life is turned upside down when she finds out that her daughter Kate has been diagnosed with leukemia.

Diaz's decision to shave off her hair though she isn't the one suffering from cancer is to express solidarity with her daughter. Whether Diaz really did shave her hair or wore a wig doesn't take away the fact that she looks very convincing as the troubled mother.

Like Diaz, there have been others who had to go for a clean look for the part. Here's a look.

The model-turned-actress did the deed for Deepa Mehta's 2006 film, which also starred John Abraham and Seema Biswas.

Nandita Das and Shabana Azmi had shaved off their heads to give their 100 percent in Water. But destiny didn't want them to star in the film, and Lisa got Nandita's role.

The film is set in the year 1938 when India was still under the British rule and when child marriage in certain sections of society was a bitter reality.

Lisa plays Kalyani, a young and beautiful widow, who lives in an ashram, and whose life is turned upside down when she falls in love.

The film also stars Kulbhushan Kharbanda and Waheeda Rehman.

Aamir beefed up for the role of a man, who loses his memory after he is bashed up by goons in A R Murugadoss's movie.

The actor also shaved his head in a very intricate design to show off the 'scars' of his injuries.

Like Aamir, Salman's character too loses his memory after being hit hard on the head in Satish Kaushik's 2003 drama. And like Aamir, he shaves off his head too.

But unlike Aamir who goes about buffing his body, Salman becomes a patient in an ashram for the mentally challenged in this very violent film.

Natalie shaved off her head for a torture scene for the 2005 film adaptation of the comic book of the same name by Alan Moore and David Lloyd.

Set in London, the science fiction-thriller is the story about a mysterious freedom fighter known only as V, who convinces Natalie's character to join forces with him after he rescues her from the state police.

More than the Daredevil himself played by Ben Affleck, it was his nemesis who caught our attention.

Bald and dangerous, Farrell played the super-enhanced human named Bullseye who is famous for his targeting skills. The lunatic killer can turn any object into a weapon and he never misses his target, thus making him very dangerous indeed.

Many have played Lex Luthor, Superman's arch-rival in movie and television versions of the comic books published by DC Comics.

While 1980's Lex Luthor played by Gene Hackman had a head full of hair, the one in the 2006 movie went bald, which made the power-mad, evil scientist more deadly looking.

To prove that women can take the punishing training regiment in order to enter the elite Navy Seals commando force, O'Niel -- played by Demi Moore -- is enlisted to be the first test subject.

Determined to succeed, O'Niel shaves off her hair, swears like a sailor and trains like a maniac to make it to the force.