Adverse childhood experiences, commonly called ACEs, are potentially traumatic events that occur before age 18. They include abuse, neglect, and various forms of household instability. Nearly two thirds of U.S. adults (63.9%) report experiencing at least one ACE, and 17.3% report four or more. The more ACEs a person accumulates, the greater their risk for serious health problems later in life.
The 10 Original ACE Categories
The concept of ACEs comes from a landmark 1998 study conducted by Kaiser Permanente and the CDC. Researchers surveyed over 9,500 adults about their childhood experiences and then compared those answers to their current health. The study identified 10 specific types of adversity, grouped into three categories: abuse, neglect, and household challenges.
The three types of abuse are emotional (being regularly insulted, put down, or made to feel afraid of being hurt), physical (being hit, grabbed, slapped, or struck hard enough to leave marks), and sexual (any sexual contact by someone at least five years older).
Neglect takes two forms. Emotional neglect means growing up without feeling loved, supported, or important to your family. Physical neglect means not having basic needs met: not enough food, no one to take you to the doctor, dirty clothes, or parents too impaired to provide care.
The five household challenges round out the list: witnessing a mother or stepmother being physically abused, living with someone who abused alcohol or drugs, living with someone who had a mental illness or attempted suicide, parental separation or divorce, and having a household member go to prison.
How ACEs Affect Long-Term Health
The original study found a striking dose-response relationship: the more categories of ACEs a person experienced, the worse their health outcomes as adults. People with four or more ACEs, compared to those with none, had 4 to 12 times the risk of alcoholism, drug abuse, depression, and suicide attempts. They had 2 to 4 times the risk of smoking, poor self-rated health, and sexually transmitted infections. Even physical inactivity and severe obesity were 1.4 to 1.6 times more common.
This wasn’t a study of people living in poverty or on the margins of society. The participants were mostly white, college-educated, middle-class adults with health insurance. That made the findings harder to dismiss as a product of disadvantage alone. Something about the childhood experiences themselves was driving the health consequences decades later.
What Toxic Stress Does to a Developing Brain
The connection between childhood adversity and adult disease isn’t just behavioral. It’s biological. When a child faces repeated threats without adequate support from a caregiver, their body’s stress response system stays activated for prolonged periods. Researchers at Harvard’s Center on the Developing Child call this “toxic stress”: strong, frequent, or prolonged activation of the body’s stress management system.
Under normal circumstances, a child’s stress hormones (particularly cortisol and adrenaline) spike briefly, then return to baseline once the threat passes. With toxic stress, cortisol levels remain elevated for extended periods. This sustained exposure can suppress immune function and physically alter the architecture of the developing brain. The brain regions responsible for fear, anxiety, and impulsive reactions overproduce neural connections, while regions dedicated to reasoning, planning, and behavioral control develop fewer connections.
The hippocampus, a brain structure critical for learning and memory, is especially vulnerable. High, sustained cortisol levels can damage this area in both children and adults. Perhaps most consequentially, toxic stress can recalibrate the stress system itself, lowering the threshold at which it activates. A person whose stress response was shaped by early adversity may react more intensely and for longer to situations that wouldn’t faze someone else. This rewiring helps explain why ACEs are linked to anxiety disorders, difficulty with emotional regulation, and heightened reactivity that persists into adulthood.
Beyond the Original 10
The original ACE study focused on what happened inside the home. Researchers and clinicians have since recognized that other childhood adversities carry similar risks. The CDC now acknowledges that the original 10 categories are not a complete list. Food insecurity, homelessness, unstable housing, and witnessing community violence all qualify as potentially traumatic experiences that can trigger the same toxic stress response.
Poverty resulting from limited educational and economic opportunities is also recognized as an ongoing source of childhood trauma. Some expanded screening tools now include experiences like racial discrimination, bullying, the serious illness or death of a caregiver, and intimate partner violence experienced by teenagers. A pediatric screening tool called PEARLS, used in medical settings, formally incorporates these broader factors alongside the original 10 ACEs. Its second section specifically captures food insecurity, housing instability, community violence, bullying, discrimination, and caregiver illness or death.
How ACEs Are Measured
ACE scores are simple counts. Each category you experienced before age 18 counts as one point, for a maximum of 10 on the original scale. The score doesn’t weigh severity or frequency. A single episode of physical abuse counts the same as years of it, and parental divorce counts the same as sexual abuse. This bluntness is a known limitation, but the scoring system has proven remarkably predictive at the population level. Higher scores consistently correlate with worse outcomes across dozens of studies.
Screening can be done in identified or anonymous formats. In anonymous versions, patients simply count how many categories apply without specifying which ones. This approach works well in busy clinical settings where the goal is a quick assessment of risk. Identified versions ask patients to specify which experiences occurred, giving providers more detailed information for follow-up.
The Economic Cost
ACEs carry an enormous financial burden. Across North America and Europe, ACE-related health conditions cost an estimated $1.3 trillion annually, representing roughly 3.5% of North America’s GDP. These estimates account for the portion of 10 major health conditions attributable to ACEs, including cancer, diabetes, cardiovascular disease, depression, anxiety, and substance use.
At the individual level, each child abuse or neglect victim in the United States costs an estimated $7,728 in child welfare services, $6,747 in criminal justice costs, and $7,999 in special education over a lifetime. California alone calculated its annual costs from substantiated abuse and neglect cases at $19.3 billion in 2017, with lost productivity accounting for the largest share at $13 billion.
What Makes the Difference
ACEs are not destiny. The same research that revealed the risks also points to protective factors. The most significant is a stable, supportive relationship with at least one caring adult. A parent, grandparent, teacher, or coach who provides consistent emotional support can buffer the effects of toxic stress by helping a child’s stress response return to baseline rather than staying chronically elevated.
This is why screening matters. Identifying ACEs early opens the door to interventions that can prevent the biological embedding of toxic stress. For adults who already carry a high ACE score, understanding the connection between childhood experiences and current health can reframe struggles with weight, substance use, mental health, or chronic disease. It shifts the question from “what’s wrong with you” to “what happened to you,” which for many people is the starting point for meaningful change.