The cry-it-out (CIO) method, also called extinction sleep training is a technique that encourages infants to learn to fall asleep independently by allowing them to cry for periods without immediate soothing from caregivers after bedtime.
It is intended to help babies develop the ability to self-soothe and settle themselves back to sleep over time. In the strictest form, the caregiver places the baby in the crib while awake and then leaves the room, not responding until a predetermined period has passed, if at all. In a modified form, periodic check-ins may occur at increasing intervals.
Parents are advised to ensure the baby’s physical needs (e.g., feeding, diapering, comfort) are met before initiating any sleep training.
To understand how the “cry it out” technique is viewed in clinical pediatrics, MedBound Times spoke with Dr. Malik Hamdan, a U.S.-based pediatrician, about how extinction-based sleep training is used in medical practice and what current evidence suggests about infant development.
“In pediatrics, ‘cry it out’ usually refers to extinction-based behavioral sleep training, either unmodified extinction or graduated extinction with timed check-ins,” said Dr. Malik Hamdan, a U.S.-based pediatrician.
“For healthy infants who are developmentally ready, typically around four to six months and older, I consider extinction-based approaches one acceptable option among several. I don’t frame it as the recommendation for every family, but as a tool that may be appropriate when parents can apply it consistently and the infant is safe and ready.”
Dr. Hamdan noted that sleep training is common in the United States, with graduated approaches frequently used in clinical practice. He emphasized that readiness, ruling out medical issues, and maintaining safe sleep practices are essential regardless of the sleep method used.
“Randomized and long-term follow-up studies have not shown evidence of lasting harm to attachment or child emotional outcomes when extinction-based sleep training is used appropriately in healthy families,” Dr. Hamdan explained.
“Crying is a stress signal, and some infants show short-term physiological stress responses early in sleep training. However, this does not equate to neglect, nor does it prove long-term neurodevelopmental harm.”
He added that attachment security depends on consistent, responsive caregiving over time, not on a single bedtime strategy used for a limited period.
According to Dr. Hamdan, extinction-based sleep training, particularly graduated extinction is a commonly used option in the U.S. for healthy infants who are developmentally ready. Current clinical evidence does not demonstrate long-term harm when these methods are applied appropriately, though short-term crying and stress responses may occur.
Foundations of CIO date back to sleep-training books and parenting guides from the late 20th century, including approaches such as “Babywise” from 1993 and others that framed sleep autonomy as a developmental milestone. These early popular methods emphasized structured routines and encouraging babies to fall asleep without external comforting aids.
Over time, the method gained attention in North America and many Western countries as a way to help both infants and parents achieve longer uninterrupted sleep. Advocates proposed that learning to sleep independently could benefit caregiver rest and overall family functioning.
Historians and child-development researchers note that structured sleep-training approaches like the cry-it-out method gained wider acceptance during and after the Industrial Revolution, when changing work patterns increased the emphasis on infant routines that aligned with fixed labor schedules.
Some research indicates that sleep training techniques including CIO can reduce night waking as perceived by parents and may lead to modest increases in sleep duration in the short term. A systematic review and randomized studies have shown that, for some infants, sleep training correlates with modest sleep improvements and no long-term adverse effects on stress hormones or behavior at later follow-up.
However, other investigators and developmental psychologists raise concerns based on attachment theory and infant signaling: crying is a primary communication tool for infants and plays a role in forming secure caregiver attachment.
Some research suggests that ignoring crying may reduce sensitive response patterns and, in theory, could influence emotional self-regulation later in life.
Studies that examine cortisol (stress hormone) during pure CIO protocols have shown elevated levels in babies during initial sessions, even when visible crying decreases, a pattern interpreted by some researchers as a stress response rather than voluntary self-soothing.
Long-term research remains limited and mixed. Some trials with follow-up years later have not found significant differences in child behavior or attachment compared with untrained cohorts, while other research critiques the methodology of these studies.
Faster sleep independence: Some studies show babies can learn to fall asleep without caregiver intervention over a period of days.
Improved parental rest: Better-structured sleep patterns may improve caregivers’ sleep quality, which can indirectly benefit overall caregiving.
Stress responses: Elevated cortisol levels have been recorded in some infants during training, even after they stop crying.
Attachment theory implications: Developmental research points to the importance of sensitive responses to infant distress for secure attachment and emotional development.
Mixed effectiveness: Some evidence indicates CIO does not cause long-term harm, but also that it may not reduce night wake-ups or improve total sleep in all infants.
In recent years, public discussion in Denmark and parts of Scandinavia has highlighted professional and cultural opposition to CIO. More than 700 Danish psychologists signed an open letter discouraging sleep training practices like “cry it out” due to concerns about attachment, infant development, and the meaning of crying as communication.
While no formal legal ban exists, Denmark’s health guidance has moved away from advocating CIO, promoting gentler, responsive caregiving and soothing strategies instead.
Some social media and blog coverage has suggested Denmark “banned” CIO outright, but professional commentary clarifies that this reflects expert consensus and cultural practice changes rather than an official legal prohibition.
Major pediatric organizations do not universally mandate one sleep-training method over another. Caregivers are encouraged to consult pediatricians before attempting sleep training, especially when infants have health or developmental concerns. All safe sleep practices, including ensuring appropriate sleep environment, responsive care, and meeting basic needs remain standard recommendations regardless of training technique chosen.
The cry-it-out method remains one of several sleep-training approaches available to families, with a spectrum of evidence and opinion in pediatric and developmental research. While many studies have not found conclusive long-term harm from structured sleep training, developmental and attachment-focused research highlights the importance of responsive caregiving. Cultural shifts, such as those seen in Denmark, reflect evolving views on infant sleep and emotional development. In all cases, choices about sleep training should be informed by scientific evidence, caregiver comfort, infant needs, and advice from qualified healthcare professionals.
References
Bilgin, A., and D. Wolke. 2020. “Parental Use of ‘Cry It Out’ in Infants: No Adverse Effects on Attachment and Behavioural Development at 18 Months.” Journal of Child Psychology and Psychiatry 61, no. 11 (November): 1184–1193. https://doi.org/10.1111/jcpp.13223.
Roy, Ishita. 2025. “What Is Denmark’s ‘Cry It Out’ Method of Putting Babies to Sleep?” Health & Me, December 17, 2025. https://www.healthandme.com/parenting/what-is-denmarks-cry-it-out-method-of-putting-babies-to-sleep-article-153300896/amp.
Ruggeri, A. 2022. “What Really Happens When Babies Are Left to Cry It Out?” BBC Future, March 30, 2022. https://www.bbc.com/future/article/20220322-how-sleep-training-affects-babies. Massey Rese
Davis, Abi M. B., and Robin S. S. Kramer. 2021. “Commentary: Does ‘Cry It Out’ Really Have No Adverse Effects on Attachment? Reflections on Bilgin and Wolke (2020).” Journal of Child Psychology and Psychiatry 62, no. 12 (December 2021): 1488–1490. https://doi.org/10.1111/jcpp.13390.
