Until this year, few people outside the R&B music scene knew who Robin Thicke was. Then came his new song "Blurred Lines" and an unrated online video to promote it.

"You the hottest b---- in this place!" Thicke sings, as topless models playfully dance around him.

The video has stirred a debate, with detractors saying it's too racy and degrading to women.

Thicke insists he meant no offense — and the song, meanwhile, has become the No. 1 hit of the summer.

In pop culture, pushing the limits of what's considered appropriate is hardly new. In the roaring 1920s, young women of the "flapper" generation raised eyebrows. In the 1950s, Elvis gyrated and caused a ruckus.

In the 1970s, comedian George Carlin joked about "The Seven Words You Can Never Say on Television," quickly listing them in a social commentary about the pitfalls of censorship.

These days, just about any kind of uncensored content is easily accessible from a mobile phone, a tablet, or on less regulated Internet TV or satellite radio. Media experts say broadcast TV and mainstream radio have tried to keep up by airing saucier content. Many see this free flow of content as a victory for freedom of expression in an uptight society.

But for many parents, it can be difficult to keep kids from pop culture offerings they don't consider age appropriate.

"It's a conundrum," says Kirsten Bischoff, a co-founder of HatchedIt.com, an online social network for families. She recalls wincing last year as her then 13-year-old daughter sang "Whistle" by rapper Flo Rida. The girls had no idea the song was about fellatio.

Those who question any kind of content risk being called a prude, or a censor. That's partly because history has shown that efforts to curb allegedly "indecent" content can look misguided in hindsight, says Susan Mackey-Kallis, an associate professor of communication at Villanova University.

In 1930, Hollywood adopted the Motion Picture Production Code, a list of moral standards for the film industry. Among other things, the code — abandoned in the 1960s for the current rating system — forbade showing interracial sexual relationships, scenes of childbirth or anything about sexual hygiene or sexually transmitted diseases. It also was implied that gay content should not be shown.

"Looking at a list like this today, it is amazing to think how far we have come," Mackey-Kallis says.

Today a decision to limit content is likely to be a business decision.

Credit card companies and the banks that oversee their transactions use web-crawling and other investigative techniques to search for questionable content. They do not, for instance, allow payments for goods or services that are related to any illegal sexual acts. They also reserve the right to steer clear of any content they feel reflects poorly on their brands.

Ultimately, however, it is the courts that determine what is obscene.

"It's clearly very tough to prove. What's obscene to some may be artful dancing to others," says Robert Pondillo, a professor of mass media history and American culture at Middle Tennessee State University who wrote the book "America's First Network TV Censor."

He also notes that the courts have not tended to limit language, which generally falls under free speech protection in the U.S.

Determining what's acceptable is further complicated by the fact that online life has changed the notion of community standards.

"We're an increasingly connected society, so we're no longer divided by our (physical) communities," says David Gudelunas, a communication professor at Fairfield University in Connecticut.

Now, communities are often online, stretching across continents and age brackets.

Take 33-year-old Ben Tao. He discovered a "niche" in the adult film industry. Crowdfunding sites such as Kickstarter, he learned, didn't allow the creators of sexually oriented projects to post those projects to seek funding.

So he started Offbeatr, a fundraising site for creators of adult films and content. His site is aimed at people age 18 and older. Those who propose projects for funding must prove their age, though he concedes it's impossible to monitor the age of everyone who visits the site.

Should society err on the side of free access, even if it means children might encounter inappropriate content?

"The entertainment industry has a huge role in deciding what is culturally OK, and society will often take (its) lead," says Jeffrey McCall, a media studies professor at DePauw University in Indiana and author of the book "Viewer Discretion Advised: Taking Control of Mass Media Influence."

Bischoff feels powerless to filter out all the content she finds inappropriate.

"There's no way to shelter a kid anymore, unless we home-school her and go live in the woods somewhere," she says. "The only thing I can think of to do as a mom is to try to stay ahead of it, with talk, talk and more talk."