Why Do Babies Smile in Their Sleep?

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.

Baby Smiling in Sleep: Reflex or Genuine?

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!)

What Happens to My Baby While They Sleep Anyway?

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.

How Much Sleep Does a Newborn Need?

Newborns will typically sleep 14 to 17 hours per day, usually scattered throughout the daytime and nighttime, says Dr. Combs. Over time, sleep will gradually decrease and move toward a more consistent schedule in terms of nighttime sleep and nap schedules.

How to Encourage Your Baby to Smile When They're Awake, Too

To help your baby learn to smile, you may consider talking, singing, and laughing with them—and smiling yourself, too. “Even at a young age, they learn to mirror expressions and emotions around them, setting the groundwork for parental attachment and self-confidence as they mature,” says Dr. Priest, adding that intentional smiling tends to occur as early as two months old. “Babies begin to spend more time awake and more time focusing on the familiar faces around them.”

Your baby will start to discover that facial expressions are a way of having “conversations” with you. Smiling is also another means of expressing their needs, in addition to crying. (Which they’ve already mastered so well!)

When you respond quickly and enthusiastically to your baby’s smiles, it lets them know they are important, which is essential for trust-building. Babies may initiate smiling (often accompanied by adorable gurgling noises), or respond to yours. Have fun with it! Make funny faces, stick out your tongue, and keep the “conversation” engaging and expressive. 

Should I Ever Worry About My Baby Smiling in Their Sleep?

Seeing your baby smile during sleep is typically not cause for concern. That said, Dr. Priest notes that any bodily twitching that cannot easily relax with gentle pressure from you should be discussed with a pediatrician or health care provider.

“Twitching or jerking that continues after a baby wakes should also be noted and discussed with a pediatrician,” she says. “Additionally, twitching or stiffening that occurs as the baby ages, occurs with illness, or occurs with poor feeding should be discussed with a pediatrician right away.”

In rare instances, gelastic seizures can occur in infants. This causes them to smile, smirk, or laugh uncontrollably, without the ability to stop on their own. If your baby’s smile seems more serious than a sleepy grin, it’s important to reach out to a health care provider.

Remember, smiling during sleep is a normal, healthy part of your infant’s growth and development! Eventually, their smile will become more frequent as they learn to express joy, trust, and comfort around those closest to them. Until then, enjoy those little grins during nap time—and remember to take plenty of pictures!