Back when my daughter was a toddler and didn’t want to go to bed, my husband and I, desperate for a decent night’s sleep, decided to try the last resort of many exhausted parents: the “cry-it-out” method. Each evening we put her to bed, kissed her goodnight, and huddled in the next room as she cried (and we did tiptoe in occasionally for a quick hug). Eventually, utterly exhausted, she’d drop off to sleep.

If you read a December Psychology Today blog post with the alarming title “Dangers of Crying It Out,” you might think the stress my husband and I inflicted on our daughter led to changes in the structure of her brain and put her at risk for developing diseases like diabetes and heart disease as an adult. The idea that something so seemingly innocuous could create ever-lasting damage is enough to make any parent want to wail all night.

But the Psychology Today post, and the many terrified responses it generated (take the horrifying-sounding “Cry It Out: The Method That Kills Baby Brain Cells”), missed something very important: Not all early childhood stress is created equal. Earlier this month, the journal Pediatrics published a wide-ranging and sensible policy statement on the lifelong effects of early childhood (that is, infancy through about kindergarten) adversity and toxic stress.

When parents stress about the wrong kinds of stress, it distracts us from a real and grave public health issue. But it’s easy to get tangled and confused by media reports about stress hurting preschoolers. Here, then, is a brief guide to the three types of childhood stress responses.

In a positive stress response, the stress hormones (like cortisol, adrenaline, and epinephrine) are revved up briefly—curdling stomachs, dampening palms, speeding up heartbeats, quickening breaths, setting the brain to high alert—and then return to their normal state. Picture a little kid freaking out when a nurse approaches with a needle or hiding under a table on the first day of nursery school. It may break your heart as a parent to witness your child’s tears, but it isn’t going to create long-lasting damage. A positive stress response is mild to moderate and—importantly—includes the presence of a supportive adult who can help the child manage the stress.

A tolerable stress response is triggered by rougher experiences: the death of family member, a serious illness, a natural disaster, a bad divorce. As with positive stress responses, as long as a caring and responsible adult is involved, the risk that the cascade of stress hormones will trigger potentially long-term consequences for health and learning plummets.

Now kick that tolerable stress response up a couple of giant notches. Remove the supportive adult from the picture, jimmy the off switch for the outpouring of stress hormones, and now we’re talking a toxic stress response. Young children who are abused, grow up with parents who are substance abusers, and have no responsible and caring adult in the picture—these are the ones who are at highest risk of suffering the damaging effects of prolonged and frequent toxic stress.

You’ve heard this before: that traumatic experiences in early childhood like neglect and abuse are common and are strongly associated with risk-taking and unhealthy lifestyles. Findings from the Adverse Childhood Experiences study, ongoing since the early 1990s, have linked these negative experiences with a higher risk for alcoholism, depression, heart and liver disease, sexually transmitted infections, teen pregnancy, and other problems. For some time now, many doctors and observers alike viewed these ailments as resulting from unhealthy lifestyles adopted as coping mechanisms by those raised in chaotic, stressful environments.

But as Pediatrics’ reports summarize, years of research have demonstrated just how utterly vulnerable—physically vulnerable—the young brain is to toxic stress. If positive stress or tolerable stress is a sudden gust that whips things up momentarily and then settles back down, toxic stress is a hurricane that can permanently damage vital structures.

Here’s how: Three key areas in the young child’s brain are highly sensitive to large and ongoing doses of the stress hormones, and each can be molded, literally, by toxic stress. Toxic stress enlarges the amygdala, a brain structure that activates the stress response, triggering excessive release of stress hormones and bumping the risk for uncontrolled fear and anxiety. The prefrontal cortex normally helps to keep the amygdala’s stress-activating role in check, but toxic stress can cause a loss of neurons and alter its ability to lessen the amygdala’s activity; affected children may have difficulty coping with stress in later years. In a similar way, toxic stress can change the architecture of the hippocampus—important in memory and mood—and impair skills related to understanding and emotion.

As a general internist who takes care of adult patients with a litany of chronic diseases, here’s what knocks my socks off: the notion that early toxic stress isn’t just vaguely bad, but can create concrete, physical effects. Unmitigated toxic stress can leave a physical mark like a tattoo, imprinted forever. No matter how normal and unstressed a child’s subsequent years, no matter how loving their parents or guardians, the early-childhood toxic-stress tattoo can doom a person to a heightened risk for chronic health problems in adulthood. Heart disease, diabetes, asthma, hypertension, autoimmune diseases: All of these can be triggered by the physical changes that result from early toxic stress. Not everybody who experiences toxic stress will end up with these problems, but the risk doesn’t go away.

This is a staggeringly huge and complicated issue that affects individual children and society as a whole. (In 2008, state and local child protective services estimated that 772,000 children were maltreated in the United States.) A number of articles have suggested various approaches toward a solution. The Pediatrics position paper calls for pediatricians to go beyond simply identifying toxic stress to referring children and parents to effective and accessible programs and resources; primary care pediatricians, they exhort, should serve as liaisons to a multitude of services that can mitigate toxic environments. Jonathan Cohn, in last month’s New Republic, calls for more spending devoted to early-childhood programs; Paul Tough in The New Yorker homes in on how treating adverse childhood experiences can improve adult health; and Nicholas Kristof implores us to improve children’s lives by reducing toxic stress early.

But to institute such major changes, parents and policymakers alike must develop a clear understanding of what childhood stress really means. It’s not a one-size-fits-all term, and frankly, discussions like that in Psychology Today are damaging and trivializing the reality of toxic childhood stress. There’s a world of a difference between one young child who cries himself to sleep with nurturing parents hovering in the next room and one who cries night after night and is never comforted.