What Childhood Experiences Leave Behind: Understanding ACEs and the Nervous System

Have you ever wondered why certain situations feel harder for you than they seem to for others? Why stress hits differently — faster, heavier, or longer-lasting than you think it "should"? Why relationships can feel complicated even when you genuinely want them to go well?

For many people, the answer is not a character flaw or a lack of resilience. It is something that happened much earlier — in childhood — and left a lasting imprint on the body and the brain.

Adverse Childhood Experiences — ACEs — can shape how we think, how we connect with others, and how our nervous system responds to stress, long after the original experiences have passed. Because the impact is not only stored in memory. It lives in the body. And understanding that matters — not to assign blame, but to make sense of what is happening now, and to find a way forward.

What Are Adverse Childhood Experiences?
The term Adverse Childhood Experiences — ACEs — comes from a landmark research study conducted in the 1990s by the Centers for Disease Control and Prevention and Kaiser Permanente. It is one of the largest investigations ever conducted into the relationship between childhood experiences and long-term health outcomes (Felitti et al., 1998).

The original ACE study identified ten categories of adverse experiences that can occur before the age of eighteen:

• Physical, emotional, or sexual abuse
• Physical or emotional neglect
• Witnessing domestic violence in the home
• Growing up with a caregiver who struggled with substance use, mental illness, or incarceration
• Parental separation or divorce

What researchers found was striking: the higher a person's ACE score, the greater their risk for a wide range of difficulties in adulthood — including mental health challenges, chronic physical illness, relationship difficulties, and problems with substance use. And these were not small effects. They were significant, consistent, and measurable across a large and diverse population.

Subsequent research has expanded the original list to include experiences such as community violence, racism, poverty, and loss of a caregiver — recognizing that the sources of childhood adversity are broader and more varied than the original study captured (Merrick et al., 2019).

Why ACEs Have Such a Lasting Impact
To understand why early experiences can shape us so deeply, it helps to know something about how the brain develops in childhood.

The human brain is not fully formed at birth. It develops over time, and the early years are especially critical. During childhood, the brain is highly sensitive to the environment — it is learning, at a foundational level, what the world is like, whether it is safe, and what kind of responses are needed to survive in it.

When a child grows up in an environment that is frequently frightening, unpredictable, or emotionally unsafe, the brain and nervous system adapt accordingly. The stress response system — designed to protect us in moments of genuine danger — can become chronically activated. The body learns to stay on alert. To anticipate threat. To react quickly, because in that environment, quick reactions were necessary for safety.

The problem is that these adaptations do not switch off when the environment changes. The nervous system that learned to brace for impact does not automatically relax once the danger has passed. It continues operating on the rules it was taught — sometimes long into adulthood (Perry & Szalavitz, 2006).

How ACEs Can Show Up in Adult Life
The effects of early adversity are not always obvious, and they do not always look like what people expect "trauma" to look like. Many people with significant ACE histories are high-functioning, accomplished, and outwardly composed. They may have no clear memory of a single dramatic event. And yet something in them quietly struggles.
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Common ways ACEs can show up in adulthood include:

• Difficulty regulating emotions — feeling flooded by intense feelings, or conversely, feeling emotionally numb or disconnected
• Chronic anxiety or hypervigilance — a persistent sense that something is about to go wrong, even in objectively safe situations
• Difficulty trusting others or forming secure attachments in relationships
• A tendency toward people-pleasing, over-giving, or difficulty setting boundaries
• Physical symptoms — including chronic pain, fatigue, digestive issues, or immune challenges — that do not have a clear medical explanation
• A deep, sometimes inexplicable sense of shame — a feeling that something is fundamentally wrong with you

These experiences are not personality flaws or moral failings. They are the long reach of a nervous system that learned to survive in difficult conditions — and is still doing what it was trained to do.

ACEs Are Common — and They Are Not Your Fault
One of the most important things to understand about ACEs is how widespread they are. The original CDC-Kaiser study found that more than sixty percent of participants had experienced at least one ACE, and nearly one in four had experienced three or more (Felitti et al., 1998).

This is not a story about rare or extreme circumstances. It is a story about how common childhood adversity is — and how quietly it shapes lives that, from the outside, may look entirely ordinary.

None of what happened to you as a child was your responsibility. Children do not cause the environments they are raised in. They simply adapt to them, as brilliantly and as resourcefully as they can. The patterns you carry now — however painful or inconvenient they may feel — began as acts of survival. They deserve to be understood with compassion, not judgment.

How EMDR Therapy Can Help
Eye Movement Desensitization and Reprocessing — EMDR — is an evidence-based therapy with a strong research foundation for treating trauma, including the kind of complex, accumulated impact that often follows a history of adverse childhood experiences (Shapiro, 2018; WHO, 2013).

EMDR works by helping the brain reprocess experiences and beliefs that became stuck in the nervous system. Many of the patterns that emerge from early adversity — the chronic alertness, the shame, the difficulty trusting or receiving care — are not simply cognitive habits. They are held in the body. EMDR is designed to work at that level, helping the nervous system update what it learned in the past with what is actually true in the present.

Unlike approaches that rely purely on talking through experiences, EMDR engages the brain's natural processing mechanisms using bilateral stimulation — most often guided eye movements. This allows the emotional charge stored in old memories and beliefs to shift, without requiring the person to relive or describe their history in extensive detail.
Through EMDR therapy, people often begin to:

• Understand — at a felt level, not just intellectually — how early experiences shaped their current patterns and responses
• Reduce the emotional intensity connected to past memories, so they feel less immediate and overwhelming
• Experience a genuine shift in the body — a felt sense of safety that was not available before
• Develop healthier ways of relating to themselves and others — with clearer boundaries and less chronic guilt or over-responsibility
• Begin to separate the past from the present — so that current relationships, situations, and challenges are no longer filtered entirely through the lens of old wounds

Your History Is Not Your Destiny
One of the most important findings to emerge from decades of ACE research is this: adversity is not destiny. The ACE score is a measure of risk and exposure — not a fixed prediction of what someone's life will look like. With the right support, the nervous system can learn new patterns. The body can begin to feel safe. The story that began in childhood does not have to be the story that defines adulthood.

Healing from childhood adversity is not about going back and changing what happened. It is about helping your nervous system understand — truly, not just intellectually — that you are not still in that environment. That you have more resources now. That you are allowed to take up space, to rest, to receive, and to trust.

The child who adapted so brilliantly to difficult circumstances deserved more than they received. And the adult they became still deserves support — not because something is broken, but because healing is possible, and no one should have to carry this alone.

If any part of this resonated with you, support is available. You do not have to make sense of this on your own.

References:
Centers for Disease Control and Prevention. (2023). About adverse childhood experiences. CDC.
Felitti, V. J., Anda, R. F., Nordenberg, D., Williamson, D. F., Spitz, A. M., Edwards, V., Koss, M. P., & Marks, J. S. (1998). Relationship of childhood abuse and household dysfunction to many of the leading causes of death in adults: The Adverse Childhood Experiences (ACE) Study. American Journal of Preventive Medicine, 14(4), 245–258.
Merrick, M. T., Ford, D. C., Ports, K. A., Guinn, A. S., Chen, J., Klevens, J., Metzler, M., Jones, C. M., Simon, T. R., Daniel, V. M., Ottley, P., & Mercy, J. A. (2019). Vital signs: Estimated proportion of adult health problems attributable to adverse childhood experiences and implications for prevention. Morbidity and Mortality Weekly Report, 68(44), 999–1005.
Perry, B. D., & Szalavitz, M. (2006). The boy who was raised as a dog: And other stories from a child psychiatrist's notebook. Basic Books.
Shapiro, F. (2018). Eye movement desensitization and reprocessing (EMDR) therapy: Basic principles, protocols, and procedures (3rd ed.). Guilford Press.
van der Kolk, B. (2014). The body keeps the score: Brain, mind, and body in the healing of trauma. Viking.
World Health Organization. (2013). Guidelines for the management of conditions specifically related to stress. WHO Press.

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