Skyler Smoot, a cooing, smiling 12-week-old baby, is in danger. His brown eyes sparkle, his toes wiggle, his hands wave, but his health lies at the heart of a controversy between parents and doctors.

“I’m just afraid, you know?” his mother, Jacklyn, says. “I’m afraid of what could happen to him.”

Skyler isn’t vaccinated.

Jacklyn Smoot, a 26 year-old new mother from Orange, California, feels torn.  Her son’s pediatrician and the Centers for Disease Control and Prevention assure her that vaccines are safe and effective. Smoot hears personal stories from vaccine skeptics like her mother, some friends, and Internet bloggers, however, who warn that vaccines can cause injury or death. She wonders who is right.

Smoot’s struggle began when she got a flu shot in December 2012. Her mother’s reaction surprised her. “She said, ‘What? But you’re pregnant!’ She scared me,” Smoot says. “I found myself online for three hours trying to figure out if it was a good idea that I had gotten the flu shot while I was pregnant.”

Six months later, on July 9, 2013, eight-pound, six-ounce Skyler Jayson was born. He got the Hepatitis B vaccine in the hospital—babies are typically given the first dose just after birth. “I just trusted them. They said that all babies get them, so I just did it,” she says.

Then she got on the Internet.

Smoot downloaded the recommended immunization schedule from the CDC website. She looked up each vaccine on the schedule. Although she says she tried to look at a variety of trustworthy websites, she can only remember reading any information supporting vaccination on the CDC website. Smoot, however, says she does not trust doctors and scientists. “I know they’re just going to tell me they’re safe, and they’re recommended, and this is what you’re supposed to do,” she says.

Dr. Neal Halsey is a professor at the Johns Hopkins Bloomberg School of Public Health and the School of Medicine. He runs the Institute for Vaccine Safety, providing independent assessment of and education on vaccine safety. “The vaccines we have available that are recommended for routine use in children are very safe vaccines,” he says.

Dr. Diane Griffin, a virologist and chair of the molecular biology and immunology department at Johns Hopkins, agrees. “Oh, yes, vaccines are very safe,” she says.

According to the CDC, vaccines in the United States are the most safe and effective immunizations in history. The CDC’s website says severe reactions to vaccines “occur so rarely that the risk is difficult to calculate.”

“I probably find more information that says vaccines aren’t safe,” she says. “I think it’s only because …” She pauses. “Well, I don’t really know. It could be maybe what I’m paying attention to more.”

Smoot also says she trusts the experiences of other parents more than data from a scientific study. “Right now,” she says, “the people telling their personal stories influence me more. I feel like the data could be flawed for one reason or another, but I feel like someone’s story, because they’ve gone through something, and they don’t want other people to go through it, I feel like I trust that more.”

The CDC website describes the years of required testing that vaccines have to pass before they are licensed. The CDC’s Immunization Safety Office constantly monitors reactions to vaccines, as do independent researchers. These experts test and retest vaccines, then confirm their results with more research. They replicate the results of other scientists to affirm their conclusions. If the data is flawed, they want to discover the flaw.

Dr. Kristin Hendrix, a professor of pediatrics at the Indiana University School of Medicine, researches how parents make decisions about their children’s healthcare, including vaccinations. “It’s a combination of pretty complex psychological factors,” Hendrix says. “Some folks are very predisposed to trust information about others’ personal experience.” She emphasizes that a story is even more likely to trump scientific data when the story comes from a friend or family member.

“Even if the situation that a person hears about didn’t actually happen to their friend or family member, but is being relayed by them, they trust that more than a face-to face conversation with a physician,” Hendrix says. “That information, anecdote, narrative, personal account, rare instance that may or may not be true, tends to carry more gravity and weight when it comes from someone they know.”

Hendrix says she thinks this preference for story over evidence may be caused by a general human tendency to misunderstand numbers, especially for risk. She says people overinflate the likelihood of something bad happening. And sometimes parents fear a negative event from a vaccination more than they fear the actual disease. She understands their perspective in some ways, she says, because illnesses like polio have been eradicated in this country. “It’s easier to believe there are no effects to not vaccinating,” Hendrix says.

Dr. Douglas Hulstedt, a pediatrician in Monetery, California, shares Smoot’s preference for personal stories over scientific evidence. Hulstedt accepts patients who are not vaccinated. He goes even further, and recommends refusing vaccinations if a patient has a family history of autism, lupus, Crohn’s disease, or Type 1 diabetes.

“Why do I need a medical study?” he says. “If 80 percent of the parents of children with regressive autism in my practice say their child reacted after the MMR [measles, mumps, and rubella] shot, why do I need a medical study?” Hulstedt says that studies showing no link between the MMR vaccine and autism or showing that vaccines are safe and effective might have “fraud in the reportage.”

Coincidentally, the one infamous study that found a causal connection between autism and the MMR vaccine, the connection Hulstedt is concerned about, was later proved to be fraudulent. Andrew Wakefield’s study, published in the British journal The Lancet and later retracted by that publication and by 10 of its 12 authors, has been blamed for much of the fear parents have of the MMR vaccine. One website Smoot found claims that Wakefield’s findings were accurate, despite the retraction. Hulstedt insisted that Wakefield’s study demonstrated a link between autism and the MMR vaccine despite a series of investigative articles by Brian Deer in the British Medical Journal in 2011 showing that Wakefield falsified medical records and data.

Halsey, of the Institute for Vaccine Safety, says he has no patience for physicians like Hulstedt. “He is putting children at risk unnecessarily and giving false information,” Halsey says. “What he is doing borders on malpractice. It is counter to the principles we follow as pediatricians. We do what is best for children.”

Like Hulstedt, Smoot fears that the personal stories blaming vaccines for a variety of chronic diseases could be true. “I am most afraid I’ll do damage to Skyler that can’t be undone—brain damage or developmental delays or anything they say can happen. It would be my fault,” she says. “I wouldn’t be able to live with that guilt.”

Griffin understands Smoot’s fears, although she emphasizes they are unfounded. Parents hear educated, charismatic people like Wakefield or Hulstedt tell them vaccines aren’t safe, she says. “Then they hear somebody else, me or Neal Halsey or the CDC, saying ‘No, you should vaccinate, it is safe, it doesn’t cause autism,’ but some people don’t have an independent way of judging who’s right and who’s wrong.”

In the end, Smoot refused Skyler’s two-month vaccinations, and he hasn’t had any more shots.

“Maybe I’ve done too much research,” she says. “It just scares me. I’m confused.”