Childhood trauma can change the way your genes behave and leave you more vulnerable to illness

And it starts happening quickly.

In the last two months, the United States government separated over 2,000 children under the age of 18 from their parents after they’d crossed the U.S. southern border. The children, some still infants, were sent to shelters, alone, with their parents detained under the Trump Administration’s “zero-tolerance” policy on immigration. Even with new pledges to end the practice of separation, there seems to be no system or plan in place to reunite these children with their families.

A wealth of medical and scientific research shows the devastating effect separation from a parent can have on children, particularly young children. The distress and upheaval are emotionally and physically overwhelming in the short-term, but such a trauma in someone’s childhood is also connected to long-term biological changes that put them at risk for psychological and medical problems throughout their lives. It’s one reason why multiple medical groups have, in the past week, condemned the practice of separating families.

“It’s a public example of institutionalized, severe trauma at extraordinarily critical periods in childhood development,” says Kerry Ressler, chief scientific officer and James and Patricia Poitras Chair in Psychiatry at McLean Hospital in Massachusetts. “This is a population that’s already at high risk due to socioeconomic and other factors, and you’re adding on to that this enormous physical and emotional trauma of parental separation. For kids certainly five to ten and younger, this is about as traumatic as a thing as you can do to them.”

Young children rely on their parents to help them handle unfamiliar, stressful situations because their ability to regulate their emotional response to change, or threats in the environment, isn’t fully developed yet. “Children use parents and familiar caregivers as a way to navigate uncertainty and stress in the world,” says Seth Pollak, who heads the Child Emotion Research Laboratory at the University of Wisconsin. “They can’t handle things alone the way adults can.”

So taking young children away from their parents and placing them in a confusing, overwhelming environment leaves them largely unable to cope. “These children are likely having really, really extreme stress, and they don’t have a way to bring that stress response down,” Pollak says.

That sort of trauma, and exposure to large amounts of stress in childhood, is linked to epigenetic changes—changes in the way that the body turns genes on and off, and regulates biological processes—that can last into adulthood. Studies show differences in the activity levels of hundreds of genes between people who experienced trauma in their childhood and those who did not, and while scientists don’t know how all of those changes affect health, there’s good evidence for the function of a few.

Most research has focused on changes to genes involved with the receptors that regulate the stress hormone cortisol. The changes in those genes, noted in both human and rodent studies, cause cortisol levels to stay elevated for longer during stressful events, and make it harder for the body to relax. “Childhood trauma, then, reshapes how the body responds to stress long-term, across the lifetime,” Ressler says. That deregulation of the healthy stress pathways leaves people at risk for depression and other psychiatric disorders.

Cortisol is also involved in the immune system, so epigenetic changes to its normal function leave people more vulnerable to illness throughout their lives. That may contribute to the increased risk of heart disease, cancer, and other adult illnesses in people who experience childhood trauma.

There’s also some evidence that early adversity and trauma changes the expression of genes for proteins involved with the growth and health of neurons. Rodent studies show that early life stress reduces the activity of the gene for brain-derived neurotrophic factor, a protein that promotes neuroplasticity and helps our brain form new connections—key for learning and cognitive function. Studies also suggest that trauma causes changes in genes involved with neuroplasticity in humans, as well.

Most of the human studies on trauma and epigenetic changes look at adults with histories of trauma from their childhood, not on children in the direct aftermath of a traumatic experience. That makes it difficult to determine the amount of time a trauma needs to last for to cause these effects, Ressler says. “Animal studies show that even a few hours of severe stress can lead to long standing marks, but for humans, it’s hard to put a specific number on it,” he says.

For the children currently detained without their parents, though, Ressler says that he suspects biological changes are already occurring. “I think, even if the separation is only on the order of days to weeks, it’s likely going to change them physically, and change the way their body and cells respond to stress for the rest of their lives,” he says.

Researchers don’t have a good grasp on the ages in childhood when trauma is likely to have the largest effect, though infancy through five or six years of age might be a key period, Ressler says. Many children under the age of five are being held in shelters separate from their parents, the Associated Press reported this week.

There’s some evidence—in rodents, at least—that a return to a stable, nurturing environment can reverse some epigenetic changes caused by early life trauma, Pollak says. “We have some biological data that the system stays plastic,” he says. However, it’s not clear how long that window might stay open for humans.

But while researchers may not have a full understanding of the specific genetic and epigenetic impacts of the separation of children from their parents, decades of consistent research from other areas of medicine unambiguously say that it’s incredibly harmful, Pollack says.

“We know taking kids away from their parents is bad, there’s a ton of scientific evidence,” he says. “And we don’t need scientific evidence to know that it’s wrong.”