How toxic stress affects child development

Toxic stress increases a child’s risk of developing emotional, behavioral, and cognitive problems. It can also trigger serious disease. How? Recent research reveals how severe, chronic stress “gets under the skin” — disregulating hormones, turning genes “on” and “off,” and altering a child’s brain.

You encounter a stressor, and your body reacts. You feel the rush of adrenaline, increasing your heart rate and blood pressure. Cortisol levels spike, triggering a surge of glucose to power your muscles. Neurotransmitters switch you into a mode that favors rapid, automatic, responses. You’re hyper-focused on sensory cues from the environment, and ready to fight, flee, or otherwise cope with the challenge at hand.

child's worried eyes peering through an opening in a wooden fence

If you’ve been startled by a velociraptor, you might experience all these physiological changes as terror. But this doesn’t change the fact that the stress response is beneficial. It enhances your ability escape. And what if the stressor is something you enjoy? Maybe you’re playing a fast-paced video game, or riding a roller coaster, or coasting down a hill on your bike. Maybe you’re feeling happily “pumped” about performing in front of an audience, or competing in a sports event. You might interpret the stress response as pleasantly exciting or invigorating.

In itself, there isn’t anything bad about the stress response. Yet we know that stress can harmful. During early life, it can even change the course of development.

So where do we draw the line between adaptive and maladaptive stress responses? When does stress become “toxic,” and what does that really mean for a child’s long-term health and well-being?

What is toxic stress?

Like most things in life, the stress response is costly, and the body pays for it by diverting energy away from normal biological functions. At the same time, the direct effects of stress hormones — like surging blood pressure, and spiked blood sugar levels — can cause harm if they continue over time. They can also disrupt normal immune function, and lead to chronic inflammation.

So while you might not suffer negative consequences from a short-lived stress response, the situation changes if you feel stressed-out every day, for weeks or months or longer. Now your body is subject to a lot of extra wear and tear, and you’re experiencing a “toxic stress response,” which experts define as:

“Prolonged activation of the stress response systems that can disrupt the development of brain architecture and other organ systems and increase the risk for stress related disease and cognitive impairment, well into the adult years” (National Academy of Sciences, Engineering, and Medicine 2019).

But how do we know about these developmental disruptions, and what do they look like? Let’s take a closer look at the evidence.

What do we know about the effects of toxic stress on children?

It makes sense that toxic stress could cause lasting damage. Chronically high blood pressure, elevated blood glucose levels, persistent inflammation — that’s a recipe for developing cardiovascular disease and metabolic disorders, like diabetes. And there are sound theoretical reasons for believing that early life stress could pose special risks. The brain is developing, so it will be more vulnerable to adverse conditions.

But of course proving causation is tricky. It’s clear, for example, that growing up in poverty exposes kids to all sorts of stressors, and these children are at higher risk for poor outcomes. But how much is attributable to toxic stress, and how much to other factors? Kids may have worse outcomes because they are malnourished, or because they receive inferior medical care.

The best way to determine causation is by performing experiments. Raise a bunch of kids under similar conditions, with one difference: Some are randomly assigned to experience toxic stress. But we can’t treat human children this way. So researchers piece together other lines of evidence — experiments conducted on nonhuman creatures, and studies that track the real-world outcomes of kids who happen to experience early life stress.

What have researchers learned? As you might expect, early life stress increases a child’s chances of developing symptoms of anxiety and depression. It’s also correlated with sleep problems in later life, and the tendency to sleep fewer hours total (Kajeepeta et al 2015). In addition, some of the most intense, adverse childhood experiences — abuse, neglect, exposure to violence, seriously ill family members, death of a parent — are major risk factors for disease, drug use, and shorter life spans (Merrick et al 2019; Grummit et al 2021).

And there’s more. In the last decade, researchers have learned about the physiological changes that accompany toxic, chronic stress. These help us understand how stress gets “under the skin” and causes lasting developmental problems.

How toxic stress alters the body’s stress response system: Two different paths

When you imagine a child experiencing toxic stress — day after day, week after week — you might assume the kid is swimming in stress hormones. In many cases, you would be correct. But the full story is more complex.

For example, it’s been confirmed in experiments on nonhuman animals, and in observational studies of human beings: Young creatures, subjected to chronic stress, tend to experience chronically high levels of cortisol. They may also become especially reactive to specific stressors, and develop symptoms of anxiety.

It’s a pattern that might persist for years. But not always.

In some cases, the body eventually adapts to a high-stress environment. Instead of pumping out stress hormones, it pulls back. It shifts down cortisol production, and becomes less reactive to daily stressors, so that an individual no longer experiences the normal spike in cortisol we’d expect when something alarming or exciting happens.

This is called a “blunted” stress response. Does it help protect kids under strain from developing certain stress-related diseases? Maybe. But it comes with its own set of problems. Kids with lower levels or cortisol and blunted stress reactivity are at higher risk for developing a variety of externalizing behavior problems, including poor emotional regulation, impulsiveness, aggression, and antisocial conduct disorders (Koss and Gunnar 2018).

So chronic, toxic stress in children can lead to two different kinds of disruptions of the stress response system, and both are associated with worse outcomes.

Early life stress and shortened telomeres

What is a telomere? Telomeres are molecules that form protective caps, or bumpers, at the ends of our chromosomes, keeping our DNA safe from damage. The longer the telomere, the better it can prevent our DNA from degrading over time. But unfortunately, the telomeres themselves tend to wear away. As we age, telomeres become progressively shorter.

When telomeres shorten at a faster pace, we experience the physiological signs of aging earlier in life. So it’s very disturbing to learn that chronically, psychologically-stressed children tend to have shorter telomeres. In particular, kids show signs of accelerated telomere erosion if they have experienced major stressors like abuse, neglect, family violence, bullying, neighborhood disorder, loss of a parent, or maternal depression (Coimbra et al 2017; Ridout et al 2018; Rentscher et al 2020). And the timing of toxic stress appears to be important. The younger the child, the more powerful the effect (Ridout et al 2018).

Toxic childhood stress can turn certain genes “on” or “off”

Our DNA is tightly coiled to fit inside the nucleus of a cell. It’s also, in places, attached to small chemical groups called methyl groups. These methyl groups have the effect of silencing nearby genes, and sometimes that’s a good thing, because it’s a gene that is better left “turned off.”

Of course there are lots of genes that we want to keep turned “on” for good health. But sometimes these genes get “methylated,” leading to trouble — including disregulated stress responses, disease, structural brain changes, and psychopathologies (like depression).

As it turns out, early life stress can cause changes in both directions — turning off “good” genes, and turning on “bad” ones. These so-called epigenetic alterations have been firmly established in controlled experiments on non-human animals. And studies of humans has documented strong correlations between early life stress and epigenetic change.

Much of this research focuses on cases where children were the victims of caregiver abuse, neglect, or bullying. But studies have also reported epigenetic changes in the wake of other stressors, like growing up in a high-crime neighborhood; living with a parent who is mentally ill or suffering from a serious physical illness; experiencing parental divorce; or experiencing the death of a parent (Houtepen et al 2018; Reuben et al 2020; Soares et al 2021).

How does toxic stress affect brain development?

Once again, we have converging evidence from both experiments and correlational studies. Early life stress affects the brain.

For example, consider children who’ve grown up with severe stressors, like maltreatment, poverty, or institutionalized care. When these kids are asked to look at emotionally-charged cues (like fearful faces), they show distinctive patterns of brain activity. The amygdala — a brain region associated with the processing emotion — becomes especially busy (Herzberg and Gunnar 2020).

There is also evidence that toxic stress influences the way the brain processes information about rewards, and the effects depend — in part — on a child’s age. When kids experience toxic stress very early in life, it may bias them in the direction of risk avoidance. By contrast, toxic stress experienced during adolescence is linked with a pattern of risk taking.

And there is striking — and disturbing — evidence that toxic stress alters the very structure of a child’s brain.

Personal and social stressors in early life have been linked with reductions in grey matter volume in the prefrontal cortex, amygdala and other subcortical regions (Tyborowska et al 2018).

In addition, numerous studies have reported links between early life stress and reduced growth of the hippocampus, a brain region associated with learning and memory. Children with hippocampal volume are at higher risk for cognitive deficits and symptoms of psychopathology (Smith and Pollack 2020).

This is all very alarming. Are children’s lives irreversibly damaged by early life stress?

It can feel overwhelming, especially when you consider how many children face serious adversity. In a recent study of more than 200,000 adults living in the United States, researchers asked how many people had experienced one or more of the following adversities during childhood:

physical, emotional, or sexual abuse;
household mental illness;
household substance use;
household domestic violence;
an incarcerated household member; and
parental separation or divorce.

Approximately 58% had experienced at least one of these adverse child experiences. More than 21% had experienced three or more (Giano et al 2020). And that translates into a large portion of the population that’s at heightened risk for the physiological, psychological, and cognitive problems we’ve discussed here. Even if your own kids aren’t affected, many of your children’s peers are.

That should inspire us to change the economic and social conditions that give rise to childhood adversity. In addition to alleviating suffering, it would be a major economic boon to society. In the United States alone, experts estimate that childhood exposure to crime and violence is costing society more than $450 billon per year (Gilad and Gutman 2019).

But even if we reduced childhood poverty and crime rates, stressors would still exist. Kids would still need our help.

And here’s what crucial to remember: Adults can do a great deal to buffer kids from the effects of stress. They can also do a lot to help children recover from distressing experiences.

As I explain in this article, caregivers can have a big impact on children’s coping skills, especially when times are tough. When parents are warm and supportive, at-risk children are less likely to suffer the medical problems and altered brain development associated with stress.

Moreover, as I note elsewhere, there’s evidence that parents can boost a child’s levels of oxytocin (a hormone that promotes feelings of closeness and calm), and reverse the harmful, epigenetic changes associated with toxic stress. It’s also clear that kids benefit from healthy social bonds. When we forge secure attachment relationships with our children, we help them develop the ability self-soothe. Read more about that here.

So while toxic stress is damaging, we can help kids recover. It’s a question of being sensitive to their needs, and creating an environment where they feel secure and supported.

More information about coping with stress, and raising healthy kids

Family members stress each other. It’s the way of things. So one of the most important ways to help kids is by attending to our own stress levels. In this article, I discuss the many factors that contribute to parental stress, and what we should do to help ourselves. In addition, I’ve prepared these parenting stress management tips. They include many evidence-based practices for coping with, and recovering from, stressors.

And check out these Parenting Science articles for promoting mental health, social harmony, and resilience:

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Content last modified 2/9/2022

image of child peering out of slat by Doidam 10 / shutterstock