A woman is beaten. Blood washes across the stage. Where do you look now?

Theatre is often uncomfortable, both intellectually and emotionally. But should it come with a warning sign?

Sydney theatre audiences are accustomed to notices posted in foyers warning of such hazards as smoke haze, herbal cigarettes, strobe lighting and loud noises. But recently these have expanded to include all manner of potentially objectionable content as a new generation of theatre-makers pushes the boundaries of what can be shown and theatre managements seek to insulate themselves against complaints.

The latest play to test audience sensibilities is the Sydney Theatre Company's coming production of Baal by the German playwright Bertolt Brecht. It was Brecht's first full-length play, written when he was 20 in the early 1920s and has been newly translated by director Simon Stone and STC associate director Tom Wright.

A note on the STC website warns that the play contains adult themes, nudity, simulated sex scenes, violence, drug references and very coarse language. It is not recommended for people under 18. (Unlike cinemas showing R-rated movies, however, the STC has no authority to deny anyone under 18 entry to the show based on their age.)

Baal is playing at the Malthouse Theatre in Melbourne. In Stone's version, the actors are naked for much of the play as Baal, an outsider poet and singer who rejects the constraints of a bourgeois society, immerses himself in sex, booze and emotional and physical cruelty. The show's early previews inspired several walkouts by audience members confronted by the nudity and violence.

On Twitter, the Malthouse playfully tweeted that "stalls rows A-F = prime scrotum section".

Audience response on Twitter has been overwhelmingly positive. One audience member, Nicola Andrews, wrote: "Awesome to see theatre that doesn't bore me to death with its timidity."

But not everyone is as open-minded. The Australian newspaper recently tagged a story on stage nudity as "high-class smut". The piece also mentioned Opera Australia's new production of La Boheme and the STC/MTC co-production of Sarah Ruhl's Pulitzer Prize-nominated play In the Next Room (or the Vibrator Play).

Smut? The very word conjures up a bygone era of censorious outrage (see panel, right). Wright regards the story as "risible" and Stone insists the nudity and profanity in Baal are a non-issue.

"There's a lot more difficult material to chew over," Stone says. "Baal is a play about a man who rapaciously eats up every form of human experience in the world until he has no experience left to live, so he dies. It's a very cruel piece of theatre."

Wright says the play would feel tepid or evasive without the nudity. "In some ways the whole purpose of this play, coming after World War I, is to re-examine the human being in its essence. You never have to think about doing Baal with nudity - the two go hand in hand. If anything, the nudity becomes a liberation."

Wright, who has had a hand in some of the most graphic depictions of sex and violence seen on Sydney stages in recent years (The War of the Roses, Women of Troy, The Lost Echo), believes our theatre audiences to be largely liberal, educated and sophisticated but thinks there is a prevailing notion that a night at the theatre should be akin to "a Tuesday night book club".

"It's a form of intellectual tourism," he says. "We often hear that people have worked hard all week and they don't want their boundaries stretched or they don't want to confront the raw truths of the human condition on stage.

"They wouldn't mind a laugh at their own expense - and that is completely legitimate. But that kind of theatre, which seeks to do nothing more than divert for an hour or two, if it's done according to current tastes and what's been done before, that art form will stagnate and die."

Wright argues that over the past 150 years, theatres have come to be regarded as a place for the betterment of society. "But sometimes it shouldn't seek to improve us or show us a better way," he says. "Sometimes you must reveal the human condition in all its maggot-ridden glory.

"A true theatrical experience involves your body responding in some way, whether it's squirming in your seat, looking away, groaning, laughing, weeping, closing your eyes in certain moments, getting fidgety. As long as your body is responding you're having a genuine relationship with the work. That's often what theatre-makers aspire to do."

As for Baal's nudity, Wright says: "It's fascinating how de-eroticised the business of acting has become. We notice it a lot on our stages - there's a pretence that the actor is a speaking head. But theatre has a subdued, and sometimes overt, eroticism. Sometimes it's useful to draw attention to that and ask the actor to literally do what they are doing metaphorically - which is revealing themselves."

The sight of naked actors might make some in the audience uncomfortable but the two things guaranteed to garner audience complaints are blood and blasphemy. Bell Shakespeare's production of Heiner Muller's Anatomy Titus Fall of Rome (2009), which involved gallons of fake blood being daubed on actors and the walls of the set, had several audience members bolting for the exits. More recently, the Canadian performer Rick Miller's Bigger Than Jesus attracted picketers concerned the play was ridiculing the Catholic Church.

Jonathan Bielski, executive producer at the Sydney Opera House, believes theatre-makers should push the boundaries even further. "I think there is not enough provocation in the theatre. It's pretty rare that there's a fuss on," he says, adding that Jerry Springer the Musical, one of the more controversial shows internationally, garnered only two complaints in Sydney.

"I don't think shocking for the sake of being shocking is interesting at all," Bielski says. "But I'd be up for more theatre- makers stirring us from our slumber in whatever way they can find is new. If someone has something powerful to say and can find a way to spark an audience into life somehow, then I think that's a good thing."

Lindy Hume, the artistic director of the Sydney Festival, agrees. In 2006, she directed Richard Mills's opera Batavia, which includes a graphic rape scene. "It was confronting to act and confronting to direct but if we'd pulled our punches it would have dishonoured the story," she says. The opera went ahead in Melbourne and Perth without warnings, Hume says, but in Sydney ticketholders were sent a letter of warning.

Hume says she tries to avoid warning audiences about strong content during Sydney Festival productions. "We don't want to hand-hold or tell people you should be frightened.

''The whole point of theatre is it should be a very emotional experience," she says. "If works are challenging, provocative or upsetting and there is artistic justification, then I wouldn't self-censor or warn the audience."

Hume says she has only once deliberately avoided programming a work she deemed too upsetting for the Sydney Festival. "I was so distressed by a piece that I just knew I couldn't sit through it again, so I didn't want my audience to go through it either. It was a valid piece and I'm pretty tough, but I couldn't sit through it again.

"Not everything can be a lovely night in the theatre. You can't have Oedipus Rex without his eyes being torn out or The Red Shoes without the girl's feet being chopped off. Those are moments of catharsis."

Do nudity or simulated sex or violence sell more tickets? Are audiences clamouring to see more? No, says Hume.

"I think people are excited by uncompromising, powerful theatre. They don't go because it's titillating or one scene is a bit spicy. You can't separate the confronting scenes from the context of the work. I think good theatre sells tickets. If it's good theatre and it contains difficult scenes, we can tell the audience to expect confronting scenes. If it's a lovely night in the theatre, we should tell them that too."

Opera Australia received a number of complaints about the lengthy fellatio scene in Neil Armfield's award-winning production of Bliss last year. More complaints rolled in for Tosca's rape scene, which insiders say is one of the reasons Cheryl Barker pulled out of the role.

The company plans to warn audiences about nudity and scenes of a graphic violent and sexual nature in the coming production of Richard Mills's The Love of the Nightingale. So far no one has complained about the topless prostitutes in La Boheme.

"You can't shock audiences any more - they've seen everything," Opera Australia's Lyndon Terracini says. "You could throw faeces at them or have everyone run about in the nude but what would be the point? The best way to shock an audience is to give them a production that moves them, a show that leaves their mouths wide open, something thrilling.

"Personally, I think there is a terrible double standard. What is allowed in film and television is far more insidious. If you're comfortable watching extreme violence and sex scenes in Underbelly, you should have no problem with Rigoletto."

Baal opens at the Sydney Theatre Company's Wharf 1 on May 7.La Boheme opens at the Sydney Opera House on July 12.