Federal officials at the U.S.-Mexico border separated nearly 2,000 children from their families between April 19 and May 31. While it’s not clear how the political fight about the practice will play out, researchers do know how a traumatic event like being separated from a parent affects a child.

“Taking children away from their mothers is harmful to them,” said Jack Shonkoff, who directs the Center for the Developing Child at Harvard University and for decades has researched how stress affects the brain. “There’s nothing complicated about that, and there’s incredibly strong science and a big hunk of common sense that both lead us to the same conclusions.”

“Taking children away from their mothers is harmful to them. There’s nothing complicated about that.”

Children being separated from their parents at the border experience toxic stress — intense, repetitive or prolonged adversity without an adult’s intervention — a situation that’s usually seen when a child is placed in an orphanage, survives a natural disaster or lives in poverty, a war zone or a refugee camp.

This kind of stress can have lifelong impact. Here’s what we know about how toxic stress affects children and what’s happening to those being detained at the border.

What does toxic stress do to the body?

When humans and animals feel threatened, their bodies produce stress hormones. This biological response triggers a chain of events that evolved to help us recognize and survive dangerous situations.

First, your amygdala — where fear registers in the brain — fires off signals. Your brain’s hypothalamus sounds the alarm for the rest of your body. Your body’s adrenal glands and tissue, located near your kidneys, release adrenaline –the “fight-or-flight” hormone — along with norepinephrine and cortisol, another stress hormone. With these hormones surging through your body, your heart races, your muscles contract, your breath quickens and your blood pressure rises. Your brain is preparing the body for how to handle trauma, said Nim Tottenham, a psychologist and researcher with the Developmental Affective Neuroscience Lab at Columbia University.

This happens when a child cries because they are hungry or throws a tantrum over a toy. In a stable environment, a familiar adult calms them, which tells their body’s alert system to stand down. In response, the child’s heartbeat slows to its normal pace. They can take a deep breath and relax.

How is this playing out along the border?

For nearly 2,000 immigrant children removed from their families and held in custody along the U.S. border with Mexico, the person who can flip that off-switch is gone. When Colleen Kraft, the president of the American Academy of Pediatrics, visited a Texas shelter this spring, she said staff were not allowed to touch children. Kraft, a pediatrician with 30 years of experience, said she saw one young girl weeping for her mother. The staff offered toys and books to console the girl, but they told Kraft they were not allowed to hold her.

“We, in this action, are inflicting toxic stress on these children,” she said.

When both children and adults are in a state of toxic stress, the brain and body are fixated on ensuring immediate survival, Tottenham said. But children are especially vulnerable because they are undergoing major brain development, which means survival takes priority over things like academic development and physical growth.

“We, in this action, are inflicting toxic stress on these children.”

Trauma that children who are separated from their parents and placed in migrant detention centers “has biological consequences on brain development in ways that are enduring for a lifetime,” Tottenham said. There is not one bellwether study that tells us separating children from their families is bad for their brains and development, Shonkoff said — there are “hundreds of studies” produced over several decades that have established the negative longterm consequences of toxic stress on children.

Some of the effects include:

Brain development

In a situation where children are separated from their parents for a long period of time, they remain on high alert, and their bodies endure prolonged and severe toxic stress as a result. That interrupts the brain’s architecture at a critical time of development, when neural circuits — the pathways necessary to carry information to and from the brain — are forming rapidly, at a rate of more than 1 million neural connections each second in infants and toddlers. Stress hormones block those neurons. This can lead to delayed development in reason, learning and emotional development. This stress can overwhelm the hippocampus, the brain’s built-in shutdown valve for the stress hormone cortisol. If continuously exposed to toxic stress over time, damage done to the child’s brain cannot be changed, studies have shown.

Emotional toll

When a child is primed to experience fear and anxiety, those emotions can superimpose themselves onto how the child interacts with another person, even if that person wants to nurture and love the child. This condition is called reactive attachment disorder, and it can start as early as infancy if a child’s basic needs aren’t met by a parent or caregiver, preventing a healthy bond from forming between them. If you try to hug a child diagnosed with this disorder, they may react by biting or hitting you, Kraft said: “Any activity with these children, even if it’s a loving activity, they’re going to react.”

In other words, children with this disorder don’t recognize nurturing behavior and therefore don’t know how to respond– so instead, they perceive these gestures as a possible threat.

Long-term effects

People often think that an infant or toddler who experiences trauma won’t remember the fear and anxiety that filled their early years once they’re placed into a stable environment, like a foster home. But “that is absolutely wrong,” Shonkoff said.

Toxic stress is more subtle than a broken bone or distended stomach, but it can leave permanent mark on a child’s brain and can “create a weak foundation for later learning, behavior, and health,” according to a 2012 study published in the journal Pediatrics that explored how adversity and toxic stress in early childhood can manifest itself throughout a child’s life.

“The bigger danger to children are the long-term consequences, and the longer they’re separated from their mothers, the greater the risks become.”

After a long period of sustained toxic stress, a child who had seemed inconsolable may become quiet, dull or withdrawn. That doesn’t mean they have adjusted to what’s going on, said Shonkoff, who led the committee that produced the 2012 study. Those symptoms emerge because their cortisol levels are depressed and their stress levels are blunted.

Long-term consequences of toxic stress are as much about physical health as they are about mental health, Shonkoff said. These children are more likely to experience behavioral problems, drop out of school, struggle with substance abuse or be diagnosed with chronic illnesses, such as diabetes or heart disease.

“The bigger danger to children are the long-term consequences, and the longer they’re separated from their mothers, the greater the risks become,” he said.

What treatments are available?

Pediatricians, including Kraft and Shonkoff, say prevention is the best cure for toxic stress in children — simply put, don’t expose them to trauma in the first place.

Therapy has been designed to combat the effects of toxic stress, but they are often expensive, need to be delivered over time and are not widely available, Kraft said. And as with any medication or therapy, individual children respond to this treatment differently. For some children, play therapy may relieve some symptoms of trauma, but for others, the strategy may not produce any real change no matter how much time is spent trying to find the right treatment.

Time is critical for delivering these services if the goal is to relieve the child from the fear and anxiety gripping them. As soon as they are identified as needing help from trauma, they need to be connected with services, said Kelly Whitener, associate professor of practice of Georgetown University’s Center for Children and Families.

The Department of Health and Human Services did not indicate when asked by the PBS NewsHour whether the federal government’s shelters provide any kind of treatment or therapy to children at-risk for or experiencing toxic stress.

To develop those kind of services would take enormous effort and cost, Shonkoff said. And even if children receive such support, Kraft said, it’s unlikely they would be fully restored mentally, emotionally and physically to who they were before they reached the United States.

What’s next?

Children in detention facilities eventually are placed in a shelter or with a sponsor while they navigate immigration court proceedings. At the same time, they are grappling with multiple levels of separation, Tottenham said. The initial trauma of watching a parent or guardian being taken away is compounded by further trauma of life going on without that person. On top of that, the child is wondering whether they will ever see that parent again.

“They’re going to be living in the United States and know that the U.S. government is the source of this trauma early in life.”

The Trump administration on Monday continued to defend the separation of children and parents at the border. The House is considering several immigration proposals, some of which address family separation, but it’s unclear at this point whether any of them have enough support.

If the policy ended today, Tottenham said entire families will need therapy and interventions to account for the trauma they have already endured. If that doesn’t happen, a population of children will grow up at great risk of developing behavior and mental health challenges, she said: “They’re going to be living in the United States and know that the U.S. government is the source of this trauma early in life.”