“Will I ever see my mommy again?”

Years later, the question still haunts me. In my career working with children who experienced caregiver related traumas, it was a question I heard all too often.

I have worked in hospitals, in community mental health centers, in schools, and with foster and adoptive care agencies. Whether children had moved between multiple foster homes, were worried about a parent being deported, or had been removed from their biological parents, the lasting effects of these early experiences were clear. The children’s symptoms often differed, from nightmares to aggression to self-harm, but the pain evident on the children’s faces, and in their questions to me, was the same each time.

The thought of being separated from one’s child is horrifying to any parent. But it pales in comparison to the potential for lifelong harm that forcible family separation will produce for the children subjected to it.

More than 2,300 children have been ripped from their parents’ arms at the southern US border since May. It’s part of the Trump administration’s new policy requiring that adults crossing the border illegally be tried criminally — a system that, in practice, has led to the forcible separation of parents from their children. Reports that children as young as 1 are being rounded up in detention cells continue to make news, including a new Associated Press report that at least three “tender age” shelters are detaining preschool-age children.

As a psychologist who studies how trauma and stress affect children’s development, I’m extremely concerned about the long-term impact of the Trump administration’s actions on these kids’ well-being

Forcible separation places these children at elevated risk for mental health disorders, including post-traumatic stress disorder, anxiety, depression, attention deficit hyperactivity disorder, and conduct problems. Epidemiological data suggest that as many as 30 percent of mental health disorders are related to childhood adversity, highlighting the widespread impact of early trauma on public health.

In many cases, the trauma of being separated from their parents could be one in a long line of stressful experiences for a migrant child. Many families seeking asylum are already fleeing danger, and many children have already endured a harrowing journey upon arriving at the border. Exposure to multiple traumatic events places these children at even greater risk for mental health disorders.

The science on this issue is clear. Parents are essential to young children’s survival, providing nutrition, warmth, and access to shelter and medical care. Beyond these needs, parents fulfill the fundamental human need for attachment early in life. In fact, the importance of caregiving for survival and healthy brain development is so great that our species has evolved a neurobiological system that encourages close parent-child bonds. Decades of research show that disruptions to stable caregiving pose substantial risks to children’s well-being.

Some of the strongest evidence for the importance of stable caregiving in families comes from research on children deprived of parental care. Even after they are adopted into stable and loving families, children who were initially reared in institutionalized care (such as orphanages) show psychological and biological consequences many years later. The list of potential effects on the children is long and grim, including but not limited to problems with sleep, eating, cognitive functioning, attention, language, social functioning, and mental and physical illnesses, many of which could persist into adulthood.

How early-life trauma impacts psychological well-being

In my work, I am often asked why traumatizing experiences that occur early in life have such lasting effects. The reason is that separating a child from their parent produces toxic stress. When a child is ripped away from a parent, their body goes into fight-or-flight mode. Stress hormones surge, and the body prepares for danger. Although this response has evolved across many generations to promote survival, severe trauma or prolonged stress can lead to chronic problems with how the body responds to stress over a lifetime.

Young children are especially vulnerable to disruptions in caregiving. The environment we live in is constantly shaping our brains, preparing our neurobiology for the kind of world we expect to encounter in the future. The brain is especially plastic early in life, such that our experiences as children have disproportionate influences on our long-term biology and physiology.

For a child who has been separated from their parent at the border, their body and brain are being shaped to anticipate danger and prepare for the worst. This state of hypervigilance, often accompanied by alterations in cognition and emotion, makes healthy functioning a major challenge.

A child whose brain is constantly scanning the environment for danger will undoubtedly have difficulty paying attention in class or interacting with peers on the playground. Some children will internalize their feelings and appear numb; others will respond by acting out. In the long run, the cascade of consequences places individuals who have experienced early trauma at risk for academic or occupational failure, substance abuse, and health problems such as heart disease and diabetes.

Even years after the parental deprivation ended, children who were initially raised in institutionalized care show hallmarks of a dysregulated stress response and disruptions in brain development. Certain networks in the brain appear to be especially vulnerable to the effects of early parental deprivation. Surges in stress hormones are more likely to influence regions of the brain that process emotion.

The amygdala, a subcortical brain structure that responds to threat, can become hijacked: Children who experienced parental deprivation show amygdala hyperactivity, meaning the brain is more likely to signal danger even when there is none. Connections with the prefrontal cortex, which are essential for quieting the amygdala, also undergo altered development following parental deprivation. All of these brain changes make it difficult for children to regulate their emotions later in life.

Parents are an integral piece in a powerful system for regulating children’s stress and emotional reactivity. Early in life, the mere presence of a parent reduces a child’s levels of cortisol, a major stress hormone, and downregulates their amygdala reactivity. One study suggests that parents help children to induce a more mature form of amygdala-prefrontal connectivity that encourages effective regulation. Thus, even at the level of neurobiology, children rely deeply on their parents for regulation early in life.

Forcibly separating children from their parents at the border strips children of their strongest buffer against stress when they need it most. The science is definite when it comes to the importance of caregiving for children’s brain development and the profound psychological and neurobiological consequences of parental deprivation. We must put an end to forcible family separation and allow these children the care of their parents to prevent lifelong harm.

Dylan Gee is an assistant professor of psychology at Yale University, where her laboratory studies anxiety and stress-related disorders and the impact of early-life trauma on the developing brain.

First Person is Vox’s home for compelling, provocative narrative essays. Do you have a story to share? Read our submission guidelines, and pitch us at firstperson@vox.com.