The cry it out method does not appear to cause lasting harm to infants, based on the available research. Studies measuring cortisol (a stress hormone) in babies who underwent sleep training found that levels actually decreased by the end of the training period, not increased. No well-designed study has linked behavioral sleep training to long-term emotional, behavioral, or attachment problems in children.
That said, “cry it out” is often used as a blanket term for several different approaches, some more intense than others. Understanding the distinctions, the appropriate age range, and a few important exceptions can help you decide what feels right for your family.
What “Cry It Out” Actually Means
Most parents use “cry it out” to describe any sleep training that involves tears, but researchers distinguish between two main approaches. The first is unmodified extinction, which means placing your baby in the crib awake and not returning until morning (or the next scheduled feeding). This is the method most people picture when they hear “cry it out,” and it’s the one that generates the most anxiety.
The second, more commonly recommended approach is graduated extinction, often called the Ferber method. With this technique, you put your baby down awake, leave the room, and return at increasing intervals to briefly offer comfort. A typical schedule might be checking in after 2 minutes, then 4 minutes, then 6 minutes, repeating the longest interval until the baby falls asleep. There’s no single correct formula for the timing. Some parents check every 5 minutes, others stretch to 10 or 15. The key difference is that you’re not disappearing entirely.
Both methods work by giving babies the opportunity to learn how to fall asleep without being rocked, fed, or held. Both involve some crying, especially in the first few nights. And both have been studied for safety.
What the Stress Research Shows
The biggest concern parents have is that prolonged crying floods a baby’s brain with stress hormones and damages development. This worry comes from research on severe neglect in institutional settings, where infants had virtually no responsive caregiving for months or years. Sleep training is a fundamentally different situation: the baby has a responsive, loving caregiver all day and is being asked to develop one specific skill at bedtime.
An AAP-associated study divided infants into a sleep-trained group and a control group, then measured salivary cortisol. Babies in the sleep training group had lower cortisol levels by the end of the process, suggesting their overall stress actually decreased once they were sleeping more efficiently. This makes sense: fragmented sleep is itself a physiological stressor for both babies and parents.
Both graduated extinction and a gentler technique called sleep fading (gradually shifting bedtime later until the baby falls asleep quickly) resulted in decreased time to fall asleep, fewer night awakenings, and lower stress markers in mothers and babies compared to controls.
Long-Term Outcomes
Several studies have followed sleep-trained children for years afterward, looking for signs of emotional problems, insecure attachment, or behavioral difficulties. None have found them. The largest and most frequently cited is an Australian trial that tracked children to age six and found no differences in emotional health, behavior, sleep quality, or the parent-child relationship between children who were sleep trained as infants and those who were not.
Researchers generally accept that for a healthy baby older than four to six months, with a consistently responsive caregiver during waking hours, behavioral sleep training does not disrupt the attachment bond. The relationship a baby has with a parent is built across thousands of daily interactions, not determined by what happens during a few nights of learning to fall asleep.
The Effect on Parents
One often overlooked piece of this conversation is what chronic sleep deprivation does to the parent. A study published in BMJ Open found that after a sleep intervention, the proportion of mothers meeting criteria for depression dropped from 32.5% to just 5%, an 85% reduction. Depression scores fell by 66% on average, anxiety by 44%, and overall stress by 42%.
These are not small numbers. A parent who is severely sleep deprived and developing depression is less responsive, less patient, and less emotionally available during the day. In many families, improving the parent’s sleep through sleep training may actually strengthen the overall quality of caregiving a baby receives.
When Sleep Training Is Appropriate
Most pediatricians recommend starting sleep training no earlier than four months of age. Some babies are ready right at four months, while others do better closer to six months. Before four months, babies have short, irregular sleep cycles, often need nighttime feedings, and haven’t developed the neurological capacity to self-soothe. Attempting any form of extinction with a newborn is not recommended.
The AAP suggests that parents can begin building healthy sleep habits as early as two months by placing the baby in the crib drowsy but awake and leaving the room. At this stage, though, a crying baby should always get a response: first a soft voice and gentle pats, then holding if needed. The goal at two months is simply familiarizing the baby with falling asleep in the crib, not formal sleep training.
Babies Who May Need a Different Approach
While the research is broadly reassuring, it comes with a caveat. Some infants may be too vulnerable for unmodified extinction. Researchers flag a few specific groups:
- Babies under six months, whose nervous systems are still maturing and who may still need nighttime calories.
- Babies with an especially sensitive or anxious temperament, who may escalate rather than settle when left alone for extended periods.
- Babies who have experienced early trauma, such as those in foster care or who have had prolonged medical hospitalizations, where the experience of being left alone could reinforce existing stress patterns.
For these babies, graduated methods with frequent check-ins, or even gentler approaches like sleep fading, are a better starting point. The goal is still the same: helping the baby learn to fall asleep independently. The pace is just slower and more supported.
What the First Few Nights Look Like
Regardless of which method you choose, the first one to three nights are typically the hardest. Crying may last 30 to 60 minutes or more on night one. By night two or three, most babies show significant improvement, and by the end of the first week, many are falling asleep within 10 to 15 minutes with little or no crying.
Parents often feel worse than the baby during this process. If you’re using graduated extinction, the brief check-ins are as much for your reassurance as for the baby’s. Knowing that the research consistently shows no lasting harm can help, but it’s also completely normal to find the experience emotionally difficult. Having a partner or support person to debrief with after each night makes a real difference.
One practical note: consistency matters more than which method you pick. Starting sleep training, giving in after 20 minutes of crying, and then trying again the next night teaches the baby that extended crying eventually works. Committing to a plan for at least a full week gives the clearest results and, paradoxically, involves less total crying than a stop-and-start approach.