Among all of your baby's first milestones, smiling is arguably one of the cutest! While you eagerly await that first gummy grin, your baby may surprise you by offering up a little smile while they're asleep, even in the first few weeks following birth.
So why, exactly, do babies smile in their sleep? Is it intentional, or something else? Here, we'll take a look at the possible reasons, what a newborn's sleep pattern looks like, and how to encourage your baby's smile when they're awake, too.
While adorable, your baby's sleepy smile is likely the result of an involuntary reflex. "Babies can make very expressive faces during different sleep stages. It's not unusual to notice a baby's seemingly first smile while they are asleep," explains Amaka Priest, M.D., a pediatrician and member of Swehl's Motherboard, the brand's panel of advisors made up of doctors, doulas, and lactation experts. "Interestingly enough, babies might also frown, twitch, smack, or suck their lips while asleep as well."
These sleep reflexes may serve as "practice" for your baby, helping them master future social skills. "Studies suggest these movements may strengthen the muscles a baby will intentionally use to smile and to make other facial expressions as they age," says Dr. Priest.
Of course, as many parents will attest to, babies may also show a reflexive smile if they are passing gas or stool. (Possibly out of relief!)
Like adults, newborns spend time in REM (Rapid Eye Movement) sleep—just a lot more of it.
"Newborns will spend up to half their sleep in REM, while adults will typically spend 20 percent of the night in REM sleep," explains Daniel Combs, M.D., board-certified in pediatrics and sleep medicine and an assistant professor of pediatrics and medicine at the University of Arizona. "Adults will typically have their first REM sleep about 90 minutes after they fall asleep. Infants will typically go straight into REM sleep."
That sweet smile you notice during nap or bedtime is likely occurring during this period of REM sleep. Dr. Combs explains that you can actually tell when your little one enters REM sleep, as they will often show frequent eye movements and twitches of their arms and legs.
"Newborn sleep is classified as quiet or active sleep, which corresponds to non-REM or REM sleep in adults," he adds. "By age 1, babies will no longer go directly into REM sleep. By age 5 or so, most children will only have 20 percent REM sleep."
Additionally, your infant's circadian rhythm (or internal body clock) is not in sync with the 24-hour day and night cycle that adults are used to, leading to erratic sleep patterns. "Most newborns can sleep in one to three-hour sleep cycles throughout the day and night. As their bodies grow and feeding needs change, those cycles can lengthen, and more sleep will occur at night," says Dr. Priest.