Breast and ovarian cancers are scary, anxiety-provoking diseases, and with good reason. Although breast cancer isn’t the cancer that kills the most women (lung cancer holds that distinction), it is the most commonly diagnosed cancer in women. And ovarian cancer is difficult to find in its early stages. But anyone willing to spit in a tube and pay $199 will soon be able to find out if they have a particular genetic predisposition to either of these cancers.

This month, the FDA granted the genetics company 23andMe permission to offer direct-to-consumer testing for three of the more than 1,000 known variants of the genes BRCA1 and BRCA2 that have been found to confer an increased risk of breast and ovarian cancer. (The tests were previously only available through a doctor.)

But not everyone is celebrating. Because the gene variants found by the test are extremely rare, most people who take the test won’t come away with much meaningful information, and there’s no good evidence that people who take the test will be better off than those who don’t.

What we have is a clash of philosophies: Should consumers have a right to information that some experts have deemed unhelpful and potentially harmful for most people (if it gives a false sense of security to those who test negative or increases anxiety)? Proponents of consumer testing say “yes.” The debate centers on how decisions about genetic testing should be made and who is entitled to a say.

One thing that there’s agreement on: The vast majority of women diagnosed with breast and ovarian cancer don’t have any known genetic factors. Only about 5 percent to 10 percent of breast cancer cases and 10 percent to 15 percent of ovarian cancer cases occur in people with a BRCA1 or BRCA2 gene variant. And the gene variants themselves are rare. The mutations detected by the 23andMe test are present in far less than 1 percent of the general population. They’re more common in women of Ashkenazi Jewish descent, but even then, they still appear in only about two out of 100 of those women.

Given the rareness of the gene variants found in the test, most people who take it won’t learn anything new, Cecile Janssens, who is an epidemiologist at Emory University and studies genetic links to disease, said in an interview. For most test-takers, being screened is like “taking a pregnancy test when you already know you are not pregnant,” she wrote in the magazine The Scientist. This is in part why the U.S. Preventive Services Task Force, an independent panel of experts tasked with making evidence-based recommendations, advises against testing for women whose family history does not suggest the presence of the BRCA1 or BRCA2 gene variants. (It recommends BRCA testing only for people with a pertinent family history.)

Advocates of testing counter that people are entitled to their genetic information. The 23andMe tests are appropriate for “anyone who wants to learn more about themselves and their potential health risks from their DNA,” said Shirley Wu, director of product science at 23andMe. And to ensure that there’s no confusion, the FDA mandates that 23andMe be clear about the limits of the test — what it can and can’t tell you. Here is an example of some of the information presented with the test results.

Anne Wojcicki, the CEO and co-founder of 23andMe, wrote in a blog post about the new test that even though there aren’t many carriers of BRCA1 or BRCA2 mutations, some women who could benefit from screening aren’t getting tested. And even if the test doesn’t change what you know about your cancer risk, Wu said, “the results can still inform your conversations with your doctor.” She said that getting a negative result on the test doesn’t mean someone should stop any healthy behaviors or screening that they would normally be doing. Just getting a genetic test helps educate and engage people in their health, she said.

Maybe the test gets people thinking about their health, but the FDA warns people who test positive on 23andMe’s test against using the result to make medical decisions. (If a 23andMe test suggests that a person has a BRCA gene variant, he or she is advised to seek confirmation and counseling from a medical professional.)

There’s ample evidence to show that genetic risk information does not change behavior, said Timothy Caulfield, who is the research director at the Health Law Institute at the University of Alberta and has studied the use of genetic testing for health promotion. For instance, one study found that giving people information about their genetic risk for developing type 2 diabetes did not change their health behaviors. And simply providing information isn’t enough to make a test useful, said Rita Redberg, a physician at the University of California San Francisco and editor of JAMA Internal Medicine. “There has to be some data to suggest that people are better off having had the test than without it, and I don’t think those criteria are met here,” Redberg said.

Ultimately, it’s up to consumers to decide whether the test will be useful for them. Janssens has been following the consumer genetics market for 10 years and said that even with the limits of the test presented in plain terms, enthusiasm for it is unlikely to be dampened. The marketing of these tests “thrives on the idea that people can make their own decisions,” Janssens said. If a customer believes that the test has utility for them, then in their view, it does, she said, “even though the rest of the world and all the experts and academics think it’s useless.”