When Nadine Burke Harris, a pediatrician recently appointed to serve as California’s first ever surgeon general, talks about her work, she invariably brings up Diego.

Diego was a 7-year-old patient who came to her clinic because he had stopped growing. He also had asthma, eczema, and behavior problems. When Harris sat down with Diego to discuss his medical history, she found out that he had been sexually assaulted as a 4-year-old. That’s when it all clicked for her. Years of treating underprivileged kids in Bayview-Hunters Point, one of San Francisco’s poorest neighborhoods, had shown her that the kids with the most severe history of trauma often exhibited the worst symptoms.

That realization would lead her to change the way she treated patients—and to become one of the chief advocates in the US medical community about how screening kids for early adversity can help them become healthier adults.

After meeting Diego, Harris starting digging. In 2008, she came across the Adverse Childhood Experiences (ACE) Study, described by the Centers for Disease Control and Prevention (CDC) as “one of the largest investigations of childhood abuse and neglect and later-life health and well-being.” That study, conducted between 1995 and 1997 by CDC and Kaiser Permanente, revealed that there was a strong correlation between a child’s exposure to traumatic experiences—including psychological, physical, and sexual abuse, or living in a violent or unstable household—and their likelihood of developing certain diseases in adulthood, including cancer, chronic lung disease, and liver disease. The study also found that ACEs were extraordinarily common in the US: More than half of the study sample of close to 10,000 adults reported at least one ACE, and one-fourth reported two or more ACEs. According to Harvard University’s Center on the Developing Child, sustained exposure to ACEs in childhood triggers the body’s toxic stress response, which negatively affects the brain, immune system, and cardiovascular system.

The study showed was that there is a biological connection between early adversity and health later in life, convincing Harris that the root cause of Diego’s symptoms could be found in his early experiences. While the science had been around for a while, Burke Harris helped popularize the use of ACEs screenings in pediatric practices, and continues to play a role in making that science accessible to a broader audience. As she later explained, “we do all of these complicated and expensive work-ups to determine the cause of our patients’ health problems, but in this case the most important thing that we had to address was the trauma.” Harris had been treating patients for years who came to her with issues ranging from behavioral problems to asthma and autoimmune disorders. The one thing they all had in common was a history of childhood adversity.

So she changed course, and opened the Center for Youth Wellness (CYW) in Bayview Hunters Point in 2010. The CYW screens kids exposed to ACEs with the ACE-Q questionnaire. Kids exposed to four or more ACEs are then given multidisciplinary treatment, including a possible psychotherapy with their parents or caregivers. As the children grow older, therapists train them to recognize the signs of toxic stress and help their minds and bodies recover. The CYW also works with clinical practices across the US to implement universal ACEs screening. The clinic is funded entirely by private donations and is free to patients.

The US health-care system tends to invest in treating diseases, not preventing them, even though science shows it is cheaper and more effective to treat the lifestyle or behavioral factors that lead to a disease, rather than try to treat the disease after it develops. In that sense, Harris is a trailblazer: She has spent a decade arguing that early intervention could help kids develop into healthier adults. Her team’s screening tool identifies ACEs in under three minutes. Then, trained professionals can use the diagnosis to encourage patients to maintain six healthy habits: sleep, exercise, nutrition, mindfulness, mental health, and healthy relationships with caring adults.

That last part is very important, which is why Harris also works to “educate parents and caregivers about the impact a child’s environment and exposures may be having on their health” and help them become a buffer for that impact, as she told The New York Times (paywall).

Not everyone believes in ACEs screenings the way Harris does. Some medical professionals say the results of the ACE study could be exaggerated because they relied on adult patients’ memory of the things that happened to them in childhood. As Paul Tough wrote in The New Yorker in 2008, “Maybe some patients misremembered or even invented their traumatic experiences; perhaps the respondents with the most wayward adult lives were the most eager to blame external forces, even imaginary ones, for their poor health.” Some pediatricians also take issue with the widespread use of the terms “toxic stress,” because they say it implies that caregivers created toxic conditions for their child to grow up in—something they believe unnecessarily shames families and gets in the way of proper treatment.

Another criticism is that the ACEs questionnaire places all forms of childhood adversity on the same level, even though some are clearly more traumatic than others. For example, a child whose parents divorced has one ACE—but so does a child who was sexually abused. And a final critique is that we don’t have many interventions to offer kids who experience ACEs. The question then becomes: Is it ethical to universally screen for a condition we still don’t fully understand and can’t offer many solutions for?

Harris would probably dispute the idea that there’s little we can do for kids who experience toxic stress. Early interventions have been shown to help kids who’ve experienced it. As Smita Malhotra, a doctor who suffers from “almost debilitating anxiety,” writes in The Washington Post: “Just as chronic toxic stress can rewire a child’s brain, the exposure to interventions that promote resilience (including trauma-focused therapy, proper nutrition, yoga and mindfulness) can help the brain to form new connections, a phenomenon called neuroplasticity. With the right tools, children can thrive despite having experienced trauma.”

Harris argues that knowledge about toxic stress can be useful for children who don’t face trauma, too. For example, she said in an interview that “one of the most important things I can do as a mom is help my children develop a healthy stress response system,” because “a well-regulated stress response is critical for kids’ success in school, relationships, jobs and in life.”

Harris has taken this science on tour across the US, giving a widely-viewed TED Talk, speaking at conferences, and organizing ACEs summits in California. She has spoken to Congress about toxic stress and worked with the San Francisco District Attorney’s Office to implement federal programs in Bayview. She has also helped pass resolutions recognizing the impact of ACEs on kids and improving trauma screening in the California legislature. Now she’s taking on a new role, as California’s first-ever surgeon general, focusing on “the social determinants” of children’s health, and bringing an early childhood development lens to governor Gavin Newsom’s administration.

Newsom’s decision to appoint Harris is a sign that he is trying to keep his campaign promises to invest in California’s early education and child-care programs and workforce. His state is already a leader in this field but, as Jenny Anderson writes in Quartz, Newsom has committed to “an aggressive early childhood agenda” with an approach that supports underprivileged and working parents.

Harris could be a crucial part of that effort. In 2018, she told The New York Times, “We need a national public campaign about toxic stress. We need to be shouting this from the rooftops.” As California’s first surgeon general, she will have a very large rooftop indeed.

Read more from our series on Rewiring Childhood. This reporting is part of a series supported by a grant from the Bernard van Leer Foundation. The author’s views are not necessarily those of the Bernard van Leer Foundation.