Jessica Alba - A screen siren crosses more than one border

Jessica Alba has so far avoided screen nudity, but her new movie about immigration sees her abandon her reserve. The Fantastic Four star tells Gill Pringle why

If most actresses will do anything to get to the top, once they arrive that often all changes as they suddenly become picky. Not so Jessica Alba. How else do you explain her steamy scenes with a man more than twice her age, not to mention a jaw-dropping nude shower scene, in the sexy "Mex-ploitation" film, Machete? Not only does the camera linger longingly over Alba as she takes the shower, it also features her in bedroom scenes with an ex-con played by veteran actor Danny Trejo, 66. We are told the underwear she wore in the shower was digitally removed afterwards, but it's still surprising for an actress who has always sworn off screen nudity.

"You think this version is sexy?! In the original script I played twins, and there was a lot more sex," she says teasingly, making it abundantly clear that she doesn't take herself too seriously.

"But I've never been very comfortable with that stuff. I get freaked out and nervous, I guess, so I told Robert [Rodriguez, the film's director], 'this is an awesome movie and I'd love to be a part of it but I don't feel comfortable doing that', and he was like, 'oh, we'll rewrite it and we'll do what you are comfortable with'."

Machete is notable not least for the audacity in casting Alba and Robert De Niro alongside more faded acts like Lindsay Lohan, Don Johnson and Steven Seagal. But, most importantly for Alba, it marks her first film playing a Latina character – a US Immigration and Customs Enforcement agent.

"Robert is a real pioneer. No one would have cast Salma [Hayek] in anything until he told them: 'Look, she's amazing'. He's really opened Hollywood up for actresses like us who refuse to play the stereotypes. And, yes, Machete is exploitative, but I also feel like we wouldn't be able to talk about the political and social messages that this movie talks about if we weren't participating in the fun of being in an exploitation movie. It's all great fun, but it also brings home certain serious messages about immigration. I grew up with road signs showing a dad, a mom and a child running in the air," she says, recalling growing up close to the Mexican-American border in San Diego, where her father worked on a nearby US Air Force base.

"Those signs are still there. It's like you see rabbits crossing and there'll be a little picture of a rabbit but then, a few miles down the freeway, you'll see a road sign showing a family and the kid would be literally flying in the air. That's what you saw driving on the freeway. And that's what I grew up with. We'd go all the time to Tijuana or Rosarito, across the border, because my dad always wanted me to stay connected with that. It's always been a relevant issue for me and Robert because we grew up with that reality, and it just happens today that a state did something really foolish and passed this very racist and foolish law, so this film has now taken on a life of its own," says Alba, 29, proud to be tapping into her Latina heritage for the first time in her 25-movie career.

She confesses she used Machete as an opportunity to brush up on her Spanish. "It was worse in the beginning and got better towards the end. But I wanted it to be like that, and my cadence was very gringa in the beginning and then at the end it had improved. But I'm really trying. At home I speak a little bit to my daughter but its just basic stuff. My goal is for her to be trilingual because we're enrolling her in a French school and then she gets Spanish every day at the house," says Alba, who wed long-time boyfriend, Cash Warren, in May 2008 in a private ceremony just weeks before the birth of their now two-year-old daughter, Honor.

Motherhood, she insists, has been transformative. "I think I'm actually a little more wild and free since I've had her because, once she's in bed, all my mom friends, we get together and have dance parties at the house. It sounds really dorky but its true. It's certainly something I wouldn't have done before," says the actress whose post-baby choices have been intriguing, ranging from this year's all-star ensemble romance Valentine's Day to serial-killer thriller The Killer Inside Me.

"I know, its weird, isn't it? I think everyone expects me to start doing family films now," says Alba, who next up appears in comedy Little Fockers with De Niro and Barbra Streisand, before reuniting with Machete director Rodriguez to play a sexy-spy mum in kids' adventure movie Spy Kids 4.

Determined to become an actress since the age of five, she was 11 when she won an acting competition in Beverly Hills, winning acting lessons which led to her being signed up by an agent. Commercials and small TV roles quickly followed, including a couple of guest spots on Beverly Hills 90210. After graduating she studied acting at David Mamet's Atlantic Theater Company, in the company of William H Macy and his wife Felicity Huffman. Aged 17, Alba auditioned with Machete director Rodriquez for his horror film Faculty, although he felt she was too young for the role. But James Cameron selected her from 1,200 hopefuls to play the part of a genetically-engineered soldier on short-lived TV series Dark Angel. She was soon cast as the eponymous star of Honey, her sexy dance moves sealing her career as a major Hollywood sex symbol and leading to bigger budget roles in Fantastic Four, Sin City and Meet Bill.

Regularly voted Sexiest Women in the World or similar, she's had almost as decade to mull over what this means: "This whole 'sex goddess' thing? Half the time, I don't even know what that means. It sounds beyond me. Way beyond me. Because I don't put myself out there to get that kind of attention. When I do, it's flattering, but it's not what I set out to do. I just want to be in movies, and I really don't see myself like this. I don't especially celebrate it but I'm grateful about it. And when I go home I wash it all away. I need to find time to be myself and not to be only a personality part of the business.

"I'm not sure what people really think about me and who they believe I am. When you see me in these magazines, it's always tailored to how they are trying to sell the movie or sell me – but this is not really me.

"I grew up Catholic so I have lots of guilt I can't seem to shake away. I'm really just a simple girl from the suburbs. But, a lot of the time, the magazines don't show that side of me. I'm proud of my heritage. I grew up in California and my great-grandparents on my dad's side are from Mexico. I'm half Mexican and the other half is French and Danish. Not so long ago, there was an idea of what an American movie star had to be, or what criteria you had to fit in to be a leading lady or man and it's changing. And I'm very glad to be part of this group of people who are ethnically diverse.

"When I grew up as a teenager, it was still a very different point of view of who the girl next door was and now it's quite different. I didn't grow up with rich girls so I really don't fit in that other group of girls. I'm a regular girl from the suburbs. The people who inspire me in real life are those who are trying to make this world better than it is. It's about all kinds of people, and I don't want to only point to people already in the eye of the media, because it's also about simple people, like my grandmother, who inspire me. Or President Obama," says the actress who has lent her name and support to numerous causes from Aids charities to The National Center for Missing and Exploited Children, as well as publicly endorsing Barack Obama and encouraging voter-registration among the young during the 2008 presidential election.

Congratulate her on her killer figure in Machete – not to mention the ability to throw a lethal kick while wearing four-inch heels – and she smiles. "I'll be honest, they were killing my feet! Walking in them isn't half as fun as putting them into someone's eye. That's for sure. I personally think it's sexier to see a strong woman.

"But I actually hate working out. I haven't worked out regularly since my daughter was three-and-a-half months old and she's more than two years old now. I know I should work out but I'm just tired. I'm doing a bit of training now for Spy Kids 4. I'm trying to get back into it. Its not easy though."

'Machete' is released on 26 November