Glossary · Sleep

What Is Cry It Out (CIO)? Sleep Training Method Explained

Definition

A sleep training method where parents put their baby to sleep and do not respond to crying until morning, allowing the baby to learn to self-settle without parental intervention.

What Cry It Out Actually Means

Cry it out, or CIO, is often used as a catch-all term for any sleep training that involves crying. In clinical sleep literature, however, CIO specifically refers to "extinction" — a method in which parents put a baby down at bedtime and do not return to the room, regardless of crying, until morning or the next scheduled feed. There are no timed check-ins and no graduated waiting periods.

The method was popularized by pediatrician Dr. Marc Weissbluth in his book Healthy Sleep Habits, Happy Child. The underlying premise is that parental check-ins can inadvertently reinforce crying by teaching the baby that crying produces parental attention — so removing the reinforcement entirely allows the extinction of the crying behavior more quickly.

It is worth noting what CIO does not mean: it does not mean ignoring your baby all night for weeks on end. Most families see dramatic reductions in crying within three to five nights. CIO also does not mean withholding feeds — parents can still do a scheduled dream feed or respond to a clearly hungry baby; the goal is to stop responding to habitual, non-hungry wakings.

The Research on Cry It Out

CIO is one of the most researched topics in pediatric sleep. A comprehensive 2006 review by the American Academy of Sleep Medicine concluded that extinction (CIO) is effective and produces rapid improvement in infant sleep with no evidence of adverse effects on child development or the parent-child relationship.

The most influential long-term study — published in Pediatrics in 2016 by Hiscock and colleagues — randomly assigned infants to three groups: extinction, graduated extinction (Ferber), or a control group with no intervention. At 12 months and again at 6 years, researchers found no differences in cortisol levels, attachment security, behavior, or emotional regulation. Children in the CIO group were not measurably more stressed, anxious, or insecurely attached than their peers.

What research consistently does show is that CIO improves maternal mental health, reduces parental fatigue, and increases overall family functioning — factors that also benefit children in the long run.

Common Misconceptions About CIO

Myth: "CIO floods babies with cortisol and causes toxic stress." This claim is largely based on misapplied research on chronic neglect, not brief periods of supported crying at bedtime. The distinction matters enormously: a baby in a safe environment with responsive caregivers who use CIO is not experiencing toxic stress.

Myth: "CIO damages attachment." Attachment is built through thousands of daytime interactions — feeding, playing, comforting, responding. A brief period of not responding to nighttime crying does not undo a secure attachment bond.

Myth: "Babies learn that no one is coming." Babies learn that nighttime is for sleeping, not for social interaction. They continue to receive full daytime responsive care. The research shows their trust in caregivers is not diminished.

Frequently Asked Questions

What is the minimum age for cry it out?

Most pediatric sleep specialists recommend waiting until at least 4–6 months before attempting CIO. Before 4 months, babies lack the neurological development needed to self-soothe reliably. Many experts prefer 6 months as a safer starting point, particularly for exclusively breastfed babies who may still have a genuine nighttime nutritional need.

Does cry it out cause lasting harm?

Decades of research have not found evidence that CIO causes lasting psychological harm. A frequently cited 2016 study in Pediatrics followed children through 6 years of age and found no differences in cortisol levels, emotional health, or attachment security between children who underwent extinction sleep training and those who did not. The brief distress of CIO does not appear to leave a measurable negative mark.

How long does crying last with the CIO method?

On the first night, crying may last anywhere from 20 minutes to over an hour depending on the baby. By night two or three, most babies cry for significantly less time. The majority of families using true extinction CIO see near-complete resolution of crying within 3–7 nights. Some babies have minimal crying after just one or two nights.

What is the difference between cry it out and the Ferber Method?

The key difference is parental involvement. Cry it out (extinction) means no check-ins — parents do not enter the room after putting the baby down. The Ferber Method is a graduated approach where parents return at increasing timed intervals to briefly reassure the baby without picking them up. Both teach self-settling, but through different levels of parental presence.

How do I know if cry it out is right for my family?

CIO is one of several evidence-based sleep training approaches. It tends to produce results quickly but requires parents to be emotionally prepared for hearing their baby cry without responding. If consistent, brief crying is very distressing for you, a graduated method like Ferber or the Sleep Lady Shuffle may feel more manageable. There is no single right method — the best approach is one your family can follow consistently.