Is sleep training (Ferber or cry it out) safe?
Research finds no lasting harm to a baby's attachment, stress, or behavior from common sleep-training methods once a baby is around 4 to 6 months old. The method matters less than picking one you can apply consistently.
What the evidence says
Studies comparing sleep-trained and non-trained infants have found no difference in attachment style and no increase in behavioral problems later on. In one study, sleep-trained babies showed lower cortisol, a stress marker, rather than higher.
Researchers have not found problematic short-term stress responses or long-term negative effects on mental health or the caregiver relationship from these methods. The discomfort of a few harder nights is not the same as harm.
Sleep training is about teaching a baby to fall asleep without being put all the way to sleep first. It is not about ignoring a baby who is hungry, sick, or in distress.
The main methods
Several approaches work. They differ mainly in how much you check in and how gradually you fade your presence.
- Graduated extinction (the Ferber method): you put your baby down awake and check in at intervals that get longer over the days. Check-ins are brief, under a minute or two, with reassurance but no picking up or feeding. It often takes about 7 to 10 days.
- Full extinction (often called cry it out): you put your baby down and do not return until morning or the next scheduled feed. It can work faster, sometimes in 3 to 4 days, but is harder for many parents to follow.
- Chair method: you sit by the crib until your baby falls asleep, then move the chair farther away each night until you are out of the room.
- Bedtime fading: you shift bedtime to match when your baby naturally falls asleep, then gradually move it earlier. This is a lower-crying option, sometimes used alongside the others.
An example Ferber check-in schedule
The Ferber method, also called graduated extinction, is built on “progressive waiting”: you check on your baby at set intervals that get a little longer each night, keeping every visit brief and calm. The minutes below are a common example, and the steady increase matters more than the exact numbers.
| Night | 1st check | 2nd check | 3rd and later checks |
|---|---|---|---|
| Night 1 | 3 min | 5 min | 10 min |
| Night 2 | 5 min | 10 min | 12 min |
| Night 3 | 10 min | 12 min | 15 min |
| Night 4 and on | Keep increasing the waits gradually, for example 12, 15, then 17 minutes, until your baby settles on their own. | ||
When to start and how to do it well
Most guidance places the start around 4 to 6 months, once night feeds are less of a biological need and your baby is developmentally ready. Talk with your pediatrician about timing for your baby.
Consistency is the single most important factor. The best method is the one you can follow night after night without changing the rules midway.
Lapses set you back. If you hold the line for three nights and then rock your baby to sleep on the fourth, your baby learns that holding out longer brings you back, which can prolong the process.
Keep your daytime routine, feeds, and bedtime steady. Always place your baby on their back on a firm flat surface with nothing loose in the crib.
Related questions
- Does sleep training harm a baby's attachment or stress levels?
- Research comparing sleep-trained and non-trained infants has found no difference in attachment style and no increase in later behavioral problems. Some studies found lower cortisol in sleep-trained babies. The evidence does not show lasting harm to mental health or the caregiver relationship when methods are used after about 4 to 6 months.
- What is the difference between the Ferber method and cry it out?
- The Ferber method is graduated extinction: you put your baby down awake and return for brief check-ins at intervals that get longer over the days. Cry it out is full extinction: you put your baby down and do not return until the next scheduled feed or morning. Cry it out can work faster but is harder for many parents to maintain.
- At what age can I start sleep training?
- Most guidance suggests starting around 4 to 6 months, once a baby is developmentally ready and night feeds are less of a biological need. Confirm timing with your pediatrician, especially if your baby was premature or has medical concerns. Whatever the start date, applying the method consistently matters more than the exact age.
Sources & further reading
ParentFlow: one free app, newborn to age six
ParentFlow is a free baby tracker that logs feeds, sleep, diapers, pumping and growth in one tap, with your daily summary, trends, and reminders based on your own logs. Free for everyday tracking on iPhone, Android, and the web.
App Store Google Play Open Web AppThis article reflects current AAP, CDC, and other public-health guidance and is for educational purposes only. It does not constitute medical advice. ParentFlow is a wellness companion — not a substitute for your pediatrician. For any medical concern, contact your healthcare provider.