When it comes to the bedroom, Viagra, Cialis and Levitra are all household words, thanks to TV, radio and Internet ads broadcasting information about erectile dysfunction around the clock, on all kinds of programming - even the Super Bowl.

So when Rachel Braun Scherl, 45, a Stanford University business school graduate, co-founded Semprae Laboratories, which developed Zestra Essential Arousal Oils, a product described as a botanical aphrodisiac, she thought bringing its message to the airwaves would be a snap. Research had shown that tens of millions of American women had sexual difficulty and no products to remedy it.

Scherl, 45, a married mother of two, and company co-founder Mary Jaensch, 58, a married mother of three, thought they had an answer for this unmet need, along with the cash to pay for ads on TV.

In an apparent double standard, many networks and some websites have declined the company's ads; a few will air them during the daytime, and others only after midnight. There is no nudity, sex, or mention of body parts, unlike ads for men's products referring to "erections lasting more than four hours."

"The most frequent answer we get is, 'We don't advertise your category,' " Scherl said. "To which we say, 'What is the category? Because if it's sexual enjoyment, you clearly cover that category. If it's female enjoyment, you clearly don't.' And when you ask for information as to what we would need to change so they would clear the ad for broadcast, they give you very little direction. ... And yet they have no problem showing ads for Viagra and other men's drugs. Why?"

Zestra's ads feature women of various ethnicities who appear to be in their 40s and 50s talking to the camera about how sex "doesn't feel the way it used to" before they had children and that their bodies "don't react" as they did when they were younger.

Zestra's website states that the oil (classified as a cosmetic) works by "heightening sensitivity to touch." The website contains endorsements by three medical doctors and the founder of a sexual health institute, and cites two clinical trials proving its effectiveness.

The oil has been featured on TV shows such as "Rachael Ray," "The Tyra Banks Show," and "Dr. Oz" and ABC's "Nightline," even though the network would allow a Zestra ad only during the late-night "Jimmy Kimmel" show, Scherl said.

A spokeswoman for Oxygen network, which accepted the ad from midnight to 4 a.m. and during "Bad Girls Club" and "Snapped," declined to specify what was objectionable about the ad during other daytime programming, citing client confidentiality.

Facebook initially ran an ad, but took it down and declined to run it again and WebMD.com declined to run ads, said Scherl.

Laura Grindstaff, an associate professor of sociology at UC Davis, said many cultures are uncomfortable with the idea of female sexuality outside reproduction and motherhood.

"When you see naked women bounding around in any music video or open a magazine and see ads for cars or cosmetics, half-naked women are everywhere," Grindstaff said. "That is not women's sexuality. What you see is completely bound up and constructed by male ideas of what women's sexuality ought to be. An ad like Zestra's, with no men in it, about women's pleasure for the sake of pleasure, is threatening, I guess. What other explanation could there be?"

Said Rita Melendez, associate professor of sexuality studies at San Francisco State University: "If they really can't run these ads, it's telling women they are not - or should not be - in control of their desire, or that there is something shameful about their sexual desire, and that has huge implications for their ability to control pregnancy, partner abuse and sexual health. You're putting something so core to women in the realm of male control, or at least outside of female control."

Industrial designer Ethan Imboden, founder of the 6-year-old luxury sex toy company Jimmyjane, said magazines and newspapers have been squeamish about covering the company's high-style vibrators, including the new palm-sized, $145 device, Form 3, often telling him they are fearful of offending readers and advertisers.

He said he has also found men to be intimidated by the thought of women's sexuality as independent of a man's involvement. Form 3, intended for use by couples, has been easier to pitch than products solely for women, he said.

"It's less indicative of any particular part of his or her anatomy, and as such, it's one step more abstract and comfortable," Imboden said.

Scherl, a consultant for women-driven businesses in pharmaceutical, beauty and health-related products, recently taught a case study at Stanford on female entrepreneurship, focusing on the risks and opportunities posed in creating Zestra, but not its advertising woes. The case study was developed before the ads were developed and rejected.

Even without widespread TV or Web advertising, Semprae's online traffic has tripled in recent weeks, Scherl said.

"It's not that we're saving the world," Scherl said, "but we are making a difference in women's lives, based on what we hear from them."

This article has been corrected since it appeared in print editions.