Why do Babies Smile While Sleeping & What Does It Mean?

Infant Smiles While Sleeping — What Does It Mean?

As a new parent, you often find yourself gawking at the sleeping bundle you brought into the world, but what you never expected was to see your baby smile back at you in their sleep. Your immediate reaction could be immense love and adoration, or perhaps amusement. But then, you start to wonder “what made my newborn smile in their sleep? Does it mean something?” We’re answering all of your sleep smile questions and helping you understand the reasons why babies smile while sleeping.

REM Sleep Cycle

Why do babies smile in their sleep? Well, It’s not entirely clear what causes it, but for starters, we can start by understanding sleep and its stages. All humans, both infants and adults, have two stages of sleep. Rapid eye movement (REM) stage and the non-REM (NREM) stage. As the names suggest, there is rapid movement of eyes underneath the eyelid in REM sleep and no movement in NREM.

Over the course of a night, you go through multiple cycles of REM and non-REM sleep. Babies begin their sleep with the NREM phase, which has 3 stages:

Stage 1: In this stage, your baby goes from being awake and drowsy, to dozing, and finally to sleep. It’s very short. Breathing slows down, muscles start to relax, and brain waves slow down. It is easy for your baby to wake up by a noise or motion in this stage.

Stage 2: Your baby moves to a light sleep stage. His or her heart and breathing further slow, and muscles relax even more than before. Eye movements under the lids stop and the brain activity slows down with sporadic periods of activity.

Stage 3: This is the deepest of NREM sleep where your baby is quiet and does not move. His heartbeat and breathing are at the slowest point, as are his brain waves. It won’t be as easy to wake him because his body is kind of in standby mode. In this very important deepest phase, his body will repair and regrow tissues, build bones and muscles, and also strengthen the immune system.

Sleep occurs in cycles, with REM occurring between the NREM phases. REM occurs between the stages of NREM sleep in the following order: NREM 1, NREM 2, NREM 3, NREM 4, NREM 3, NREM 2, REM, NREM 2. . .

Newborn Smile Reflex

In the ‘REM’ phase of sleep, your baby may happen to smile, laugh, jerk, whimper, cry or jump. Since it’s impossible to really know whether babies dream, it’s believed that when babies smile or laugh in their sleep, it’s often a reflex rather than a response to a dream they’re having. For example, many researchers note that babies may twitch or smile in their sleep during active sleep. When babies go through this type of sleep, their bodies can make involuntary movements. These involuntary movements might contribute to smiles and laughter while sleeping.

Dreams and Smiling

There are skeptics who question the ability of babies to have a solid dream like adults. Our dreams are made up of past events, experiences, and interactions. They also involve dialogs and a sense of ourselves and people that we know or make up in our minds. A newborn won’t have the necessary mental skills yet, to make up complex things like dreams.

During the first months of their lives, when babies smile and laugh while they are sleeping, those actions are only a subconscious response from their brains, which happen most likely when the baby is drowsy or during REM stages of sleep. 

Developing Emotions

There have long been signs that newborn smiles could signal positive emotions to some extent. Smiles have been noted in the first few days of life as a response to stroking of the cheek or the belly. Newborns also smile in response to sweet tastes and smells. It is thought that while awake, their developing brains record all their daily experiences, which possibly gets processed while they are asleep. The happy emotions felt while soaking up these new experiences may show through smiles or laughter in their sleep. Hence, smiling or laughing while asleep is thought to be part of the process of developing their human emotions.


Smile Meanings

While the “sleeping baby” smiles may be caused by developing emotions, or the REM sleep cycle, there are still different types of smiles too. Yes, babies have different types of smiles with different meanings, and these smiles appear at different milestones in their lives. If a newborn baby smiles in his sleep, his smile falls into one of three categories: Reflexive, Responsive, and Social.

Reflexive Smile

When do babies start smiling you ask? Well, as early as 0 to 6 weeks you may spot your baby’s first smile. Within the first few days of birth, your little one will demonstrate fleeting smiles while asleep. During REM, your baby's body goes through physiological changes that activate certain reflexes, and smiling is one of them. Experts are of the opinion that these episodes of early smiles in babies are reflex actions similar to other reflexes shown by newborn babies, like sucking and rooting. These reflexive smiles are not triggered by emotion, but are nature’s way of allowing your baby to practice different skills. In fact, reflex smiles may happen while the baby is in his mother’s womb from 25 to 27 weeks of gestation. After birth, reflexive smiles may typically occur during the REM sleep phase.

Responsive Smile

As your baby grows to around 6 to 8 weeks, he’ll start to smile in response to sensory experiences he finds pleasurable - cuddles, familiar voices and faces, the comfort of his Woolino sleep bag, etc. His smile is a reaction to sensory experiences, not a social response, so don't expect too much at this stage. Babies only learn about smiling and laughing as an expression of joy later on in their lives, around month 3 to 4 or even later than that. As much as you’d like to think of these smiles as confirmation that you’re the best mom in the world, responsive smiles are not social reactions. However, you can still try to encourage a smile by giving your baby plenty of opportunities to study your face while you talk gently. Responsive smiles can help you learn about your baby’s likes and dislikes, what amuses him or what makes him grin. Imitate his expressions, and he may start to imitate yours.


Social Smile - Emotional Changes

By 3 to 4 months, your baby should enter the social stage where he wants to connect. Up until this point, his infant smiles were internal reactions to things that caught his attention. Now he is capable of identifying you as his primary caregiver and will smile when he sees you. He will also be able to react when you make silly sounds, and learn to get a reaction from you by smiling. Now, there's no question you're his favorite. 

Passing Gas

The notion that a baby’s smiles infer that he is passing gas is not supported by any concrete scientific research. Nevertheless, it is a known fact that colicky babies tend to remain irritable, and farting brings relief and helps them feel better. So one of the reasons for smiling during sleeping could be that your baby is passing gas.

Other Medical Causes

Your baby smiling while sleeping is rarely something to worry about. But if you notice other symptoms such as weight loss, trouble while sleeping, frequent irritability, or laughing for no apparent reason, you should take him to a doctor. The occurrence of convulsive laughter episodes can disrupt your baby’s rest and negatively impact his health.

Remember as well, that your baby won't always smile when you want him to, and he also has to express other emotions. But if you notice your baby not smiling at all by 12 weeks, tell your pediatrician so that he can check for developmental delays.

In Conclusion

Watching your infant smiling while sleeping is not only heartwarming, but an important sign that your baby is developing emotionally and physically. It is essential that you understand that each baby can have varied learning curves and developmental milestones. Unless you’re experiencing sleep disturbances or issues with sleeping, don’t worry if your baby doesn’t display certain milestones at the exact time as others. Let your baby develop at his own pace and enjoy the little moments with him.


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