Like most professional pundits, Margaret Cuomo has perfected the art of speaking authoritatively even when she does not know what she is talking about. Unlike most professional pundits, Cuomo is in a position to cause real damage. As a celebrity doctor spreading misinformation about the hazards of vaping, she is actively discouraging smokers from making a switch that could save their lives, thereby undermining her avowed goal of A World Without Cancer.

That's the title of a book that Cuomo, a radiologist who is the sister of New York Gov. Andrew Cuomo and CNN anchor Chris Cuomo (as well as the daughter of former Gov. Mario Cuomo), published in 2012. Given Cuomo's medical degree and her experience in diagnosing and writing about cancer, any layman unfamiliar with the subject would be inclined to believe her statement, in a Huffington Post video posted on March 14, that "e-cigarettes will raise your risk for lung cancer but also other cancers, like liver cancer." But as Boston University public health professor Michael Siegel (who is also a physician) was quick to point out, "there is absolutely no evidence to support this claim," which Cuomo retracted after The Daily Caller's Guy Bentley asked about it.

A new, hastily edited version of the video omits the cancer claim. Also gone: claims that tin has been detected in the aerosol produced by e-cigarettes and that vaping generates hazardous chemicals that are not found in tobacco smoke (which Siegel called "an outright lie"). But the corrected video still features a statement that sums up Cuomo's take on vaping. "Because of their chemical composition," Cuomo says as the video begins, "e-cigarettes are at least as harmful to your health as regular tobacco cigarettes are." A caption drives the point home: "They're not a safer cigarette."

How does Cuomo know that? She doesn't, because it's not true. E-cigarettes, unlike the conventional kind, do not contain tobacco and do not burn anything, so they do not generate the 7,000 or so chemicals found in cigarette smoke, which include hundreds that are toxic or carcinogenic. While a few of those worrisome substances have been detected in e-cigarette vapor, they are present at much lower levels. According to a 2013 analysis of 12 brands that was reported in the journal Tobacco Control, "The levels of potentially toxic compounds in e-cigarette vapour are 9–450-fold lower than those in the smoke from conventional cigarettes, and in many cases comparable with the trace amounts present in pharmaceutical preparations."

A 2015 report from Public Health England emphasized the enormous difference in risk between e-cigarettes and the real thing. "While vaping may not be 100% safe," it said, "most of the chemicals causing smoking-related disease are absent and the chemicals which are present pose limited danger. It has been previously estimated that [electronic cigarettes] are around 95% safer than smoking. This appears to remain a reasonable estimate."

Siegel thinks even that estimate, which means vapers face 5 percent the risk that smokers face, exaggerates the hazards of e-cigarettes. "Based on the evidence that's out there," he recently told The San Diego Union-Tribune, vaping is "much, much safer—orders of magnitude safer….My impression is that 5 percent is way too high. That would be about 20,000 deaths a year [if all smokers vaped instead], and I don't think that's feasible."

In short, there is no scientific basis for Cuomo's warning that "e-cigarettes are at least as harmful to your health as regular tobacco cigarettes are." Not surprisingly, she cites no evidence to support the claim, other than to mention four carcinogens (benzene, cadmium, nickel, and formaldehyde) that have been detected in e-cigarette vapor. She does not mention the tiny amounts involved, which are far lower than the amounts found in tobacco smoke (except in experiments that deliberately overheat vaporizers to produce unusually large amounts of formaldehyde), or that the list of problematic chemicals in tobacco smoke is much longer. Saying we know e-cigarettes are just as dangerous as tobacco cigarettes "because of their chemical composition" may sound scientific, but it's complete nonsense.

The Huffington Post amplified Cuomo's blatantly inaccurate warning with its original headline: "Doctor Explains Why E-Cigarettes Are Just As Dangerous As Tobacco Cigarettes." That headline can still be seen on the website, over a post that no longer includes the Cuomo video but does include a correction mentioning the three inaccurate statements that were excised from it. "There's a misconception that e-cigarettes may be a better alternative to tobacco cigarettes," the post says, "but according to Margaret Cuomo, the author of A World Without Cancer, the two are both dangerous." Even if two products are "dangerous," of course, one can still be much less dangerous than the other, as in this case.

The headline over the new version of the video is notably different from the original headline: "Why E-Cigarettes Are Dangerous to Your Health." That phrasing leaves open the possibility that e-cigarettes are nevertheless safer than conventional cigarettes—a possibility that Cuomo still denies in the opening line of the video. Her position in the original version could be ascribed to ignorance, which would be bad enough for someone presenting herself as an expert. But her decision to stick with it even after the error was called to her attention suggests something worse: either a deliberate attempt to mislead people or a desire to save face by pretending that her central thesis is still valid despite the misrepresentations she already has admitted.

The Internet is full of people saying demonstrably wrong things about all sorts of subjects, including e-cigarettes (as Michael Siegel doggedly documents on his tobacco policy blog). But as a medical professional engaged in public education (or, in this case, miseducation), Cuomo has a special obligation to get things right. By stubbornly insisting that vaping is just as dangerous as smoking, she does a potentially deadly disservice to smokers who may decide, based on her advice, that they have nothing to gain from switching.

This article originally appeared at Forbes.com.