Why Do Babies Smile In Their Sleep?

Baby smiling in sleep on mother's lap. Nestled in a blue shawl. Mother is white with palm around baby's right ear. Mother wearing grey leggings, spotted with a red print
Mother and baby.

Thanasis Zovoilis

Watching your baby smile in their sleep is very high up on the cuteness scale—right beside their baby grip and those first cute attempts at clapping. But while a captured smile during sleep makes for a great addition to your memory book, you could also be witnessing something revealing about your child’s growth and development.

Why Do Babies Smile?

When a baby smiles, the typical response is not to ask why, but to fawn excessively in hopes of producing more. However, because milestones like smiling and crawling can be used to track your baby's progress, special notice may be paid to the reason for your baby's toothless grin.

Reflex Smiles

This type of smile is usually short and may occur without any real reason. You may notice that your baby begins to really smile at around 3 months. In reality, however, they may have been able to melt a heart or two with their smiles while tucked away in your belly.

Studies have shown that fetuses are capable of smiling at around 33 weeks of gestation.This type of smile is often described as a reflex action—much like kicking or sucking the thumb in the womb. They can happen without a reaction and usually do not need visual stimulation to occur. 

Gas

Another potential reason for smiling could simply be that your baby has gas! Babies have been described as smiling while passing gas or stool.

Social Smiles

At around the three-month mark, you may notice a change in the way your child picks and chooses moments to smile. By this time, they have been given the opportunity to interact with their environment. Babies may have learned some social cues. Social smiles appear around this time as a sign of attentive engagement with an interactive caregiver.

Regardless of whether or not it is reflex, social, or in reaction to passing gas, you can choose to interpret your child's smile the best way you see fit. The important thing is that they are healthy and engaging with their environment.

How Does REM Affect Your Baby’s Smile?

It may look peaceful on the outside, but a lot goes on in our bodies as we sleep. We'll be taking a sneak peek into our heads to understand how the kinds of sleep we experience help to put smiles on our faces as we snooze.

Your body will typically go through two basic types of sleep: rapid eye movement (REM) and non-rapid eye movement (non-REM) sleep. You go through all stages of each type of sleep several times a night. We'll be taking special notice of REM sleep, which is where smiling during sleep is most likely to occur. 

There are 3 stages of non-REM sleep:

  • Stage 1: Here, your body is making the shift from being awake to heading into a light sleep. It lasts for several minutes where your heartbeat, breathing, and eye movements will slow. You'll also experience your muscles start to relax.
  • Stage 2: This is the phase before you transition from light to deeper sleep. It is characterized by slower heartbeats and breathing. You'll also notice your muscles start to relax even further. This is our body's most repeated stage of sleep.
  • Stage 3: In this stage, your body is in deep sleep. Your heartbeat and breathing slow to their lowest, while your muscles relax even further. 

REM sleep

This occurs after about 90 minutes of sleep. In this phase, your eyes will move rapidly about behind your eyelids, and you start to get closer to waking. Your breathing gets quicker and irregular, while your heart rate and blood levels increase to around the points experienced during waking hours.

In this phase of sleep, you'll experience some temporary paralysis in your leg and arm muscles to prevent you from getting a little too enthusiastic and acting out your dreams.


If you notice your baby smiling or laughing while asleep, it is probably happening during this phase, although it is more accurately known as "active sleep" in children.

Studies have shown that babies may experience smiles, grimaces, body twitches, and sucking in this phase.

Reviewing Reasons Babies Smile During Sleep 

Babies smile on reflex without exactly meaning to, or without it being in reaction to a person or thing. As time goes on, you may notice your little one smile when passing gas or stool, perhaps in response to the enjoyable feeling.

There are also instances where babies have sensory responses to taste or smell. It isn't unheard of for babies to stretch out a smile when they come in contact with a smell or taste they find pleasant.

As children become more familiar with their environment, you may notice your baby start to smile when they see a familiar face, or perhaps because they are aware it will produce a reaction from you. When it comes to babies smiling in their sleep, however, there's still some grey area.

Since we have no way of knowing if babies dream, or what they dream about, it may be a safe assumption that their smiling which typically occurs during active sleep is a reflex action, and is most likely involuntary. 

In the event that babies do dream however, a smile in their dream could be in reaction to a memory that occurred during the day, or an event strung together by their subconscious.

Could a Baby's Smile Be a Warning Sign?

Catching a baby's smile during sleep is always a joy to experience. However, there are rare occasions where this smile may be telling of something more serious at hand.

Gelastic seizures are an extremely rare form of epilepsy. This condition is usually observed with uncontrollable fits of laughter. In some moments, sounds similar to laughter may be combined with the face contorting into a smile. Gelasitic seizures may also feature flushing, a rapid heartbeat and altered breathing.

These seizures are extremely rare, making up about 1% of all epileptic cases. While rare, if you are concerned that your baby may be experiencing this type of seizure, seek medical help immediately.

How to Make Your Baby Smile

As your baby becomes more aware of their environment, it's easy to catch them smiling at one object or the other, or simply expressing joy that you are there and present with them. Your baby smiling in reaction to events is also a good way to observe that their senses are working properly as they make use of them to become more conscious of their environment.

These moments can be incredibly wholesome, so it's understandable to want your baby to smile often. While it's certainly okay if your baby doesn't smile as often as you'd like them to, here are some ways that might generate more grins from your baby:

  • Engage with your baby during interactions like feeding, dressing, and bathing.
  • Read to your baby.
  • Sing to your baby.
  • Make funny faces at them.
  • Match your baby's reactions—when they smile, return a smile to them.
  • React with enthusiasm when your baby giggles, sucks, burps, or otherwise responds positively to their environment.

A Word From Verywell


For such a little movement, on such a little person's face, baby smiles are capable of producing big reactions of happiness and excitement from others. A baby smiling in their sleep is a completely normal reaction and an expected part of their development. If your child frequently smiles in their sleep, it could mean nothing more than a reflex reaction, or perhaps they are merely replaying a happy memory from earlier in the day.

Learning about why your baby smiles, cries, coos, and more, is an exciting part of the process of getting to know and love your child. However, should you have any questions or concerns about your baby's wellness or development, it's always a good decision to consult with their pediatrician.

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