The actress gained 10 lbs., chopped her hair and got some piercings for the role

Albert Michael/Startraks

For her role in the upcoming Gimme Shelter, Vanessa Hudgens didn’t just play her character — she became her character. “The tattoo, the hair, the clothes, the piercings, the attitude, the everything,” she tells PEOPLE. “The walk, the talk … it was a completely new person. I really did look like a boy.” Gaining 10 lbs. for the role, plus chopping her hair and adding several piercings “automatically puts you into a different headspace,” she says. “Not to mention the places we were filming. We were in the grimiest, dirtiest places, and I was fighting every day, being fought, being beat down and it was all extremely draining even though it was acting.” Speaking to PEOPLE Monday at Neutrogena’s Wave for Change event in Los Angeles, the actress, still sporting cropped hair, said life has calmed since filming — and aside from a summer of skydiving and tattooing, she’s happy to be helping a good cause. “I love working with charities, I love children, and there is so much we can do,” she said. “Wave for Change makes it super easy for kids to make a difference and give back.” Hudgens, Hayden Panettiere and Miranda Cosgrove each designed a tote bag for Wave for Change, available through Aug. 31 for those who purchase two Neutrogena products at Target. For each product purchased, Neutrogena will donate one dollar to — up to $250,000. Hudgens explained that her tote was made to help disaster relief victims. “It’s ‘Hope,’ because everybody needs hope in times of need,” she said. “Some of the inspiration came from the movie … my character names her baby Hope.” Panettiere, also a face of Neutrogena, told PEOPLE that hers was designed with animal charities in mind. “It’s in the shape of a heart, but it’s made up of dolphins and whales and birds and stingrays and swordfish,” she explained. “It was definitely a collaboration.” —Reporting by Reagan Alexander