WWW- LINDSAY Lohan is suffering for her art – that is, suffering bruises from dancing on a stripper’s pole to prepare for her role as a topless dancer in her new movie, “I Know Who Killed Me.”

Lohan, 20, who sometimes forgets her underwear in real life, has been taking classes in the art of undressing – and she got a lesson in occupational hazards.

An e-mail she sent to pals last week has the subject title: “They’re all whores, they’re all whores . . . xcept for some obviously!” Lohan wrote in the note, “So . . . 3 hours of pole dancing and bruised. everywhere . . . I mean we’re talkin’ like, UPPER AND INNER THIGH ACTION-bruised . . . like a walking black-and-blue mark.

“I mean really though, really, I didn’t know it was actually possible to have bruises in such areas of the body. Strippers dude, I tell you, I really respect the [c-word]s now. . . I’m not gonna lie to ya.”

Lohan’s rep, Leslie Sloane Zelnik, said, “She’s been in rehearsals for the film and has been taking classes from Sheila Kelly.” Kelly developed the famed “S Factor: Aerobic Striptease Workout and Pole Dancing.”

“Her character is a stripper, and she now realizes that the job isn’t easy. We should give these women credit,” Zelnik told Page Six.

Lohan faces five more weeks of bruised thighs while she completes the picture, but that hasn’t stopped her from going out. She’s gone to clubs in L.A. almost every night during shooting. But, much to her friends’ and family’s relief, she hasn’t been drinking and has been making it to work on time.

An inside source said, “When the shoot is over, she is going to focus her attention 100 percent on staying sober and building a more fruitful life.” Lohan may also move back to New York in a bid to get away from “the toxic L.A. scene with all those toxic people.”

Sadly, Lohan seems to be as addicted to those “toxic” people – including her “frenemy” Paris Hilton – as she is to parties. She was out Thursday night partying once again with Hilton, whom she alternately swears she hates and loves.