The presidents of the National Academies of Sciences, Engineering, and Medicine issued a statement Wednesday advocating for the U.S. Department of Homeland Security to stop separating migrant families. The statement cites research that indicates endangerment of those involved. Last week the American Psychological Association released a letter opposing the Trump administration’s policy of taking immigrant children from their parents at the border. Under the zero-tolerance immigration policy, since May more than 2,300 immigrant children—some of them babies—have been forcibly separated from their parents attempting to enter the U.S. from Mexico.

Also Wednesday, as the backlash and public outcry continue to grow, Pres. Donald Trump said he would sign an executive order to stop separating families at the order. It was unclear when children already separated might be reunited with their families. But even if reunited soon, medical experts say the effects of separation can potentially last a lifetime.

Scientific American spoke with Alan Shapiro, assistant clinical professor in pediatrics at Albert Einstein College of Medicine, about the effects of separation trauma and other health and mental consequences of breaking up families. Shapiro is also senior medical director for Community Pediatric Programs (CPP), a collaboration between the Children’s Hospital at Montefiore in New York City and the Children’s Health Fund, and medical director and co-founder of Terra Firma, a partnership that provides medical and legal services to immigrant children.

[An edited transcript of the conversation follows]:   

Are immigrant children especially susceptible to trauma? And if so, why?

These children have already been exposed to enormous amounts of stress and trauma. You need to look at what happened to them in their country of origin that triggered them to leave, and what happened on the journey. Almost across the board they have witnessed, or been victims of, sexual or physical abuse and gang and political violence.

For young children, but really for all children and people, dislocation—whether it’s internal displacement or actually fleeing a country, or both—is an extremely disruptive event. The journey itself means giving up all the stability in their life: their home, school, friends, family, community and culture, everything. Then they have to make the journey, sometimes a 2,000-mile journey, not traveling with a luxury bus or airline. They’re walking for miles, taking freight trains, riding on the back of traveling trucks and exposed to extremes of temperature, injury, sleep deprivation and sometimes violence or kidnapping. All the families that travel to the border have to undergo this stress and trauma before they enter the country. Then they enter the country, not trying to sneak by the guard—no one’s trying to bypass immigration—just following the route they know. And they are put into these processing centers, enormous warehouses that are freezing cold, windowless and have the lights on 24/7, so they’re very disorienting. This is where many of them split up into these cages, known as kennels or iceboxes. This is where separation starts.

What are some of the acute effects of separation on children?

Separation leads to depressive symptoms: We see children who might have gained certain milestones of development start regressing all of a sudden. You see this in children who are exposed to various forms of trauma, even in children who are with their parents in their homes, who lose everything and end up in a homeless shelter. You’ll also see changes in their sleeping patterns—children who stop eating, who become aggressive or very clingy to their parents—these are really symptoms of acute stress. There’s a story of a boy who was separated from his father and just stopped talking.

I’ve been to a number of detention centers over the past few years, such as the Brooks County Detention Center in Falfurrias, Texas. Even in those detention centers where children are kept with their parents, you see signs of depression and acute stress. We also see self-mutilative behavior where kids are biting or trying to hurt themselves. In kids that I’ve seen, one was chewing on his arm, another on his fingers, and one kept trying to choke himself—all signs of acute stress.

What are some of the long-term issues these children might face?

The younger you are when you’re exposed to stress (the longer, more prolonged stress), the more likely you will have negative health outcomes caused by dysregulation of stress response. If you’re confronted with danger your body produces cortisol, epinephrine and norepinephrine—inflammatory hormones to protect and help you deal with danger—essentially allowing a fight-or-flight response. So your heart rate goes up, certain cortical areas shut down and you are able to fight back. When that happens over long periods of time and a child is constantly exposed to a threat, it leads to dysregulation of stress response. The hormones are elevated and stay elevated, meaning they don’t go back down to normal levels once that threat has gone away. So if you remove a child from a parent there’s a constant threat for who knows how long, and that change in the dysregulated stress response leads to architectural changes in the brain—which means that in the future children might end up with serious learning, developmental and health problems.

There’s a famous, 17,000-patient study called Adverse Childhood Experiences (ACEs), which shows that adults who had more adverse childhood experiences are much more likely to have chronic medical conditions like cardiovascular disease, hypertension, obesity, higher rates of cancer and a decrease in longevity. We don’t know if these are going to happen to these children. But there’s no reason that it wouldn’t, so it’s really worrisome that the government is actually endangering the lives of children.

How does the length of separation impact its effects? Is it proportional?

I can’t give you a coefficient, but in general the principle is the longer the duration of stress and trauma, the lengthier the outcome will be. We all know from post-traumatic stress disorder (PTSD) studies on army vets that some people are just more resilient than others. Those are factors that are inherited in people. But in general, the more prolonged the exposure to stress and to trauma, the worse the outcomes will be.

We tend to talk less about the parents. What are the effects of separation on the mothers and fathers of these children?

We recently heard of the father who killed himself, and we focus a lot of the attention on the child—rightly so—but the effect on parents is also fairly devastating. The impact on the adults is severe. At the Brooks County Detention Center, we saw real desperation amongst the mothers: Many scored positively on major depressive screening scales Patient Health Questionnaire-9 (PHQ-9). I heard mothers disclose suicidal ideation and feelings of loss of control over not being able to properly parent and protect their child. There were very deep levels of depression, and feeling that their children couldn’t depend on them and their children lost respect for them because they couldn’t get them out of detention. It’s devastating to hear these women talk about their own feelings of powerlessness.

The last thing is, do we have to wait for a child to die for this policy to end? I really worry about putting 1,500 kids in a Walmart or 400 children in a tent city in the desert where it’s 110 or 120 degrees. It is just a matter of time before something really bad happens.