The short answer, based on the best available evidence, is no. Cry it out does not appear to cause lasting emotional harm or trauma in healthy infants when used at an appropriate age. A five-year follow-up study published in Pediatrics found no measurable differences between children who went through behavioral sleep training as infants and those who did not, across emotional health, conduct, stress levels, psychosocial functioning, and parent-child relationship quality. That said, the picture is more nuanced than a simple yes or no, and the details matter.
What “Cry It Out” Actually Means
The term gets used loosely, so it helps to clarify. True cry it out, called “unmodified extinction” in clinical literature, means placing your baby in the crib awake, saying goodnight, and not returning until morning (unless you suspect illness or danger). As one Cleveland Clinic pediatrician describes it, “It’s almost like going cold turkey.” Some babies cry for a few minutes. Others can cry for hours, especially the first few nights.
Most families who say they did “cry it out” actually used a gentler version called graduated extinction. With this approach, you check on your baby at increasing intervals but don’t pick them up or feed them back to sleep. Many families see significant improvement within three to seven nights with this method. The distinction matters because most of the reassuring long-term research studied graduated methods, while the study that raised the most concern specifically used full extinction.
The Cortisol Study That Sparked Concern
Much of the fear around cry it out traces back to a 2012 study by Wendy Middlemiss and colleagues. The researchers measured cortisol, a stress hormone, in 25 infants going through a five-day inpatient extinction program. On the first night, when babies cried, both mothers and babies had elevated cortisol, and their stress levels moved in sync. By the third night, the babies had stopped crying at bedtime, but their cortisol levels remained elevated. Meanwhile, the mothers’ cortisol had dropped because they no longer heard crying.
This finding, that babies appeared physiologically stressed even after they stopped showing it, understandably alarmed parents. Critics interpreted it as evidence that babies simply learn to give up signaling rather than actually feeling calmer. The study is real and worth taking seriously, but it has important limitations. It involved only 25 infants over five days in an institutional setting, not a home environment. It measured cortisol at only two time points during the program. And it did not follow up to see whether cortisol levels normalized in the days or weeks that followed. Elevated cortisol during a stressful transition is expected in infants; the question is whether it persists long enough to cause harm.
What the Long-Term Evidence Shows
The strongest evidence on lasting effects comes from a randomized controlled trial that followed 225 families for five years after sleep training. Researchers assessed children’s emotional behavior, conduct, sleep quality, psychosocial functioning, and chronic stress levels. They also measured parent-child closeness, conflict, and attachment patterns. The results were striking in their consistency: there were no significant differences between sleep-trained children and controls on any measure. Children’s emotional behavior scores were statistically identical. Parent-child closeness and conflict showed no difference. The children’s own self-reports of wellbeing matched the control group.
The researchers’ conclusion was blunt: behavioral sleep techniques have no marked long-lasting effects, positive or negative. This doesn’t mean sleep training is emotionally meaningless to a baby in the moment. It means the stress of a few difficult nights does not appear to leave a detectable imprint on development, behavior, or the parent-child relationship years later.
Attachment Security and Sleep Training
The deeper fear behind the trauma question is usually about attachment: will my baby stop trusting me? Research on this has been reassuring. A study of 94 one-year-olds found that attachment security, measured through the Strange Situation procedure (the gold standard assessment), was not associated with sleep problems or how parents handled night waking.
There is one important caveat. Research by Morrell and Steele found that infants who already had insecure attachment patterns showed exaggerated distress responses to extinction methods, and the approach was more likely to fail and potentially reinforce both the sleep problems and the attachment difficulties. This doesn’t mean cry it out caused the insecure attachment. It means that for babies who are already struggling with attachment, extinction methods may not be the right tool.
The Difference Between Stress and Toxic Stress
Not all stress is harmful. Developmental scientists distinguish between three types: positive stress (brief, mild, part of normal learning), tolerable stress (more intense but buffered by a supportive caregiver), and toxic stress (severe, prolonged, and without adequate adult support). Toxic stress is what damages developing brains. It’s associated with chronic neglect, abuse, household chaos, and caregiver absence over months or years.
A few nights of crying at bedtime, in the context of a baby who is well-fed, healthy, loved, and responded to throughout the day, does not meet the criteria for toxic stress. The baby’s overall relationship with their caregivers across hundreds of daily interactions is what shapes attachment and brain development, not isolated episodes of distress at bedtime.
Benefits for Parental Mental Health
One aspect often left out of the trauma debate is what chronic sleep deprivation does to parents. A study published in BMJ Open found that after a sleep intervention, the proportion of mothers experiencing depression dropped from 32.5% to 5%, an 85% reduction. Anxiety decreased by 44%, and overall stress by 42%. Parental depression and exhaustion directly affect the quality of caregiving a baby receives during waking hours. A well-rested parent who is emotionally available during the day may be a greater protective factor than avoiding a few nights of bedtime crying.
When to Avoid Sleep Training
Sleep training is not appropriate for every baby. Most pediatric sleep experts agree it should not be used before four to six months of age, and some recommend waiting until eight to twelve months to allow for natural developmental changes in sleep patterns. Younger infants have genuine physiological needs for nighttime feeding and are not developmentally ready to self-soothe.
Other situations where extinction methods are not recommended include babies who are ill, premature infants who haven’t reached corrected age milestones, and infants who already show signs of insecure attachment. If a baby has a medical condition affecting sleep, such as reflux or ear infections, those issues need to be addressed first. The American Academy of Sleep Medicine’s guidelines emphasize that behavioral interventions assume there is no underlying physiological problem driving the night waking.
What This Means in Practice
If you’re considering sleep training and worried about causing trauma, the evidence suggests that for a healthy baby over six months of age, in a stable and loving home, a few nights of crying at bedtime will not damage your child’s emotional development or your relationship with them. The five-year follow-up data is about as reassuring as developmental research gets.
That said, you don’t have to use unmodified extinction if it feels wrong. Graduated methods, where you check on your baby at intervals, are equally effective for most families and feel more manageable for parents. The Middlemiss cortisol study is a legitimate reason to prefer a gentler approach, even if its long-term significance remains unclear. Sleep training works best when parents feel confident in the method they choose, because consistency over three to seven nights is what actually produces results.