What do you call someone who sows misinformation, stokes fear, abets behavior that endangers people’s health, extracts enormous visibility from doing so and then says the equivalent of “Who? Me?”

I’m not aware of any common noun for a bad actor of this sort. But there’s a proper noun: Jenny McCarthy.

For much of the past decade, McCarthy has been the panicked face and intemperate voice of a movement that posits a link between autism and childhood vaccinations and that badmouths vaccines in general, saying that they have toxins in them and that children get too many of them at once.

Because she posed nude for Playboy, dated Jim Carrey and is blond and bellicose, she has received platforms for this message that her fellow nonsense peddlers might not have. She has spread the twisted word more efficiently than the rest.

And then, earlier this month, she said the craziest thing of all, in a column for The Chicago Sun-Times.

“I am not ‘anti-vaccine,’ ” she wrote, going on to add, “For years, I have repeatedly stated that I am, in fact, ‘pro-vaccine’ and for years I have been wrongly branded.”

You can call this revisionism. Or you can call it “a complete and utter lie,” as the writer Michael Specter said to me. Specter’s 2009 book, “Denialism,” looks at irrational retorts to proven science like McCarthy’s long and undeniable campaign against vaccines.

McCarthy waded into the subject after her son, Evan, was given a diagnosis of autism in 2005. She was initially motivated, it seems, by heartache and genuine concern.

She proceeded to hysteria and wild hypothesis. She got traction, and pressed on and on.

In 2007, she was invited on “Oprah” and said that when she took Evan to the doctor for the combined measles-mumps-rubella vaccine, she had “a very bad feeling” about what she recklessly termed “the autism shot.” She added that after the vaccination, “Boom! Soul, gone from his eyes.”

In an online Q. and A. after the show, she wrote: “If I had another child, I would not vaccinate.”

She also appeared on CNN in 2007 and said that when concerned pregnant women asked her what to do, “I am surely not going to tell anyone to vaccinate.”

Two years later, in Time magazine, she said, “If you ask a parent of an autistic child if they want the measles or the autism, we will stand in line for the measles.” I’ve deleted the expletive she used before the second “measles.”

And on The Huffington Post a year after that, she responded to experts who insisted that vaccines didn’t cause autism and were crucial to public health with this declaration: “That’s a lie, and we’re sick of it.”

I don’t know how she can claim a pro-vaccine record. But I know why she’d want to.

Over the last few years, measles outbreaks linked to parents’ refusals to vaccinate children have been laid at McCarthy’s feet. The British study that opponents like her long cited has been revealed as fraudulent. And she and her tribe have gone from seeming like pitifully misguided dissidents to indefatigably senseless quacks, a changed climate and mood suggested by what happened last month when she asked her Twitter followers to name “the most important personality trait” in a mate. She got a bevy of blistering responses along the lines of “someone who vaccinates” and “critical thinking skills.”

Seth Mnookin, the author of the 2011 book “The Panic Virus,” which explores and explodes the myth that vaccines cause autism, noted that McCarthy had a relatively new gig on ABC’s “The View” that could be jeopardized by continued fearmongering. What once raised her profile, he said, could now cut her down.

As she does her convenient pivot, the rest of us should look at questions raised by her misadventures.

When did it become O.K. to present gut feelings like hers as something in legitimate competition with real science? That’s what interviewers who gave her airtime did, also letting her tell the tale of supposedly curing Evan’s autism with a combination of her “Mommy instinct” and a gluten-free diet, and I’d love to know how they justify it.

Are the eyeballs drawn by someone like McCarthy more compelling than public health and truth? Her exposure proves how readily television bookers and much of the news media will let famous people or pretty people or (best of all!) people who are both famous and pretty hold forth on subjects to which they bring no actual expertise. Whether the topic is autism or presidential politics, celebrity trumps authority and obviates erudition.

There’s also this: How much time did physicians and public officials waste trying to neutralize the junk in which McCarthy trafficked? As Fred Volkmar, a professor at Yale University’s medical school, said to me, “It diverts people from what’s really important, which is to focus on the science of really helping kids with autism.”