Parents of infants and young children regularly consult their pediatricians about how to get their child to fall asleep at the beginning of the night or how to get their child back to sleep after a middle-of-the-night awakening. Prevalence rates for these types of sleep disturbances have been reported to be as high as 20% to 30% for 1- and 2-year-olds.1,2
Optimally, at some point during the first year of life, an infant should be able to self-soothe, both when falling asleep and after an awakening during the night. How do such self-soothing behaviors become established?
As a prelude to understanding the emergence of nighttime self-soothing behaviors, it is necessary to appreciate the developmental course of sleep, and night waking in particular. During the first few months of life, an infant awakens, on average, every 3 to 4 hours throughout the day and night, usually requiring parental comforting or feeding to return to sleep. By 3 or 4 months of age, the infant’s longest period of continuous sleep has lengthened and shifted to the nighttime hours. By 1 year of age, infants are typically sleeping for 6- to 7-hour stretches during the night.3,4
As the first year progresses, more and more parents report that their infants have “slept through the night.” By the time the child is 8 to 9 months of age, 70% of parents report that their infant sleeps through the night regularly.5
Sleeping through the night, however, is technically a misnomer. Several studies using objective methods instead of parental report have demonstrated conclusively that infants continue to awaken periodically through the night.3,6
Thus, although the longest period of sustained sleep has lengthened, it does not span the entire night. Surrounding the longest sleep period are shorter bouts of sleep, punctuated by arousals and awakenings. Arousals can be as brief as 30 seconds or can lead to full awakenings that result in infants either self-soothing or requiring parental presence to reinitiate sleep. Thus, even at 1 year of age, infants rarely sleep through the entire night without several awakenings or arousals. Instead, it is the infant’s ability to self-soothe that emerges, allowing parents to sleep through the night.
Clearly, some infants acquire the ability to self-soothe during the first year of life, whereas others continue to awaken their parents, potentially causing a great deal of stress for the family. Recent research has shown that self-soothing is rarely an “all or nothing” construct.7
Most infants alternate between self-soothing and needing assistance on the same night or on consecutive nights over the first year of life, but tend to lean toward one style or the other. When parental comfort is required persistently beyond an age that parents expect, a sleep problem is presented to the pediatrician.8,9
It is important, then, to understand how infant self-soothing behaviors evolve and why they may not develop in some children. Factors associated with infant self-soothing at night include the mode of feeding (nursing vs formula), sleep location (crib vs family bed), bedtime and nighttime interactions with the parent, and use of a sleep aid.7,10
In general, infants are more likely to self-soothe after 4 to 6 months of age when they are not nursed during the night, sleep alone in their own cribs, fall asleep on their own with minimal parental contact, and have access to, and make use of, a sleep aid.
One way that parents promote self-soothing is through the encouragement of the use of sleep aids. A number of studies have reported that infants’ use of sleep aids is associated with self-soothing.5,11,12
A sleep aid is defined as any object (including parts of the child’s own body) that a child uses in his/her sleeping environment to facilitate sleep without requiring parental assistance. Several studies have examined children’s use of objects, both during the day and at night. The use of a special object at night seems to be quite common among young children in Western cultures. One study reported that 44% of children between the ages of 6 months and 4 years used some type of object at bedtime,13
and another reported that between 16% to 72% of children aged 3 to 60 months were attached to a pacifier, blanket, or hard object.14
Age seems to be a significant factor in determining both the likelihood of a child’s attachment to a special object as well as the type of object that is used.13–15
Two studies have looked at cross-cultural patterns of sleep aid use. One investigation comparing American and Korean children reported that pacifier use is most common among infants under 6 months of age, whereas soft objects are used most often by older infants and preschoolers, regardless of cultural origin.16
The incidence of object use seems to vary greatly between cultural groups, however. American infants are much more likely to use objects for soothing than are infants in Korea or Guatemala.16,17
One potential reason for this difference is that in many non-Western cultures, there is more physical contact between infants and mothers during the day and night, and infants are not expected to fall asleep on their own. Indeed, regardless of culture, infants tend to use sleep aids when they are expected to fall asleep on their own.13
Some objections have been posed to the use of objects at night. The American Academy of Pediatrics has recommended that soft objects, including pillows, blankets, and stuffed toys, be kept out of the child’s crib.18
The position of the American Academy of Pediatrics stems primarily from a concern that objects contribute to an increased risk for sudden infant death syndrome. The largest risk seems to occur when an infant is placed on top of a soft sleeping surface, such as a sheepskin or pillow.19
Potential sleep aids need to be chosen with these recommendations in mind. Parents who value the practice of cosleeping also may object to the introduction of sleep aids, with the thought that an object is not a valid substitute for a parent in soothing a young child.20
The study of sleep aid use is most applicable to Western parents who want to promote self-soothing.
There are 2 main limitations to the extant research on sleep aid use. First, previous studies of nighttime object use have relied mostly on parental report,13–17
the validity of which is uncertain. It is possible that parents are not aware of objects that children may use after parental departure at bedtime or during the middle of the night. Indeed, if children fall back to sleep on their own, parents are often unaware that an awakening occurred at all.3
The second limitation to existing research is that previous studies have relied on cross-sectional designs to infer what occurs across age.13–16
There are no longitudinal studies of object use at night.
Furthermore, there have been no studies to date that have attempted to facilitate the development of self-soothing by introducing a novel sleep aid during the first year of life. One stimulus that seems to be particularly attractive to infants is their mothers’ scent. Given a choice between a pad scented with an unfamiliar mother’s breast milk and a pad scented with their own mother’s breast milk, even very young infants will orient toward their own mother’s scent.21
Nonhuman mammalian studies also support the importance of maternal olfactory cues in early neonatal orienting and settling behavior.22
It is likely, then, that an object that smells like the mother may be an attractive sleep aid to an infant. The use of maternal odor as a component of a novel sleep aid was explored initially in a small pilot study, the results of which were inconclusive.23
The current investigation was designed to assess whether introducing a sleep aid infused with maternal scent at different ages would impact infants’ self-soothing. A separate investigation, to be reported elsewhere, assessed the effects introducing a scented versus a control sleep aid on self-soothing. In addition to examining the use of the specific, novel sleep aid, the current study examined other types of objects that parents spontaneously provided their infants. Given the results of previous work, it was expected that infants who used a sleep aid would self-soothe more than infants who did not use a sleep aid. The study also examined infants’ use of both the novel and parent-provided sleep aids over a 3-month period to see whether infants tended to persist in using 1 object, or tended to use different objects as they grew.
In addition to addressing these 2 primary questions, the current study attempted to examine 3 subsidiary issues raised by previous research. To ascertain the degree of accuracy in parental report of sleep aid use, objective data obtained from nighttime video recordings were compared with what parents reported. In addition, parents were asked to rate their comfort with different types of sleep aids; these data were then compared with actual sleep aid use to determine the concordance between the 2. Finally, to examine whether sleeping context may impact the use of sleep aids, infants who slept in their own rooms versus their parents’ rooms were compared.