Parenting
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When do babies start smiling? The science behind that first grin
Cradlewise Staff
Your baby locks eyes with you, their lips curl upward, and suddenly, there it is – a grin so tiny, yet it feels like the whole world just got brighter. It’s one of those heart-stealing moments that makes every sleepless night and every tired morning feel worth it.
You lean closer, waiting, hoping it wasn’t just a one-time thing. And when it happens again, your heart does a little happy dance.
Parents often wonder about this magical milestone: when will it happen, what sparks it, and how does it change the way we connect with our little ones?
In this blog, we’ll unwrap the when, the why, and the pure joy of your baby’s first smile, along with some sweet and surprising tidbits that will make you look at those tiny grins in a whole new light.
When do babies start smiling?
According to the American Academy of Pediatrics, babies usually begin showing their first social smiles around the end of the second month, often between 6 and 8 weeks of age. Pediatricians often look for this milestone during a 2-month visit, since it signals early social and emotional development.
Parents sometimes believe their newborn is smiling from day one, but experts explain that these early grins are reflexes rather than true smiles. They often happen randomly or are linked to sensations like gas, not to social interaction.
The first real smile, which is a direct response to a parent’s face or voice, usually appears a few weeks later and marks an important step in bonding and communication.
The two stages of smiles: Reflex smiles and social smiles.
Reflex smile
In the first few weeks, your newborn’s smiles are mostly reflexes. They happen when your baby is drowsy, drifting off to sleep, or sometimes just because their nervous system is practicing movements. These smiles aren’t tied to feelings yet. Think of these reflex smiles as “test runs” for the real thing.
Social smile
Around 6 to 8 weeks, your baby flashes a smile in response to you. This is the social smile, your baby’s first way of saying “I see you, I know you, and I like what’s happening!”
It’s rooted in brain development and bonding. Also, it’s one of the earliest signs of emotional connection. It is the “you’re my favorite person” smile, the one you’ll never forget.
Did you know the babies smile in the womb?
Evidence published in the Association for Psychological Science shows that between 32 and 36 weeks of gestation, researchers captured 4D ultrasound footage of babies laughing. They showed that fetuses whose mothers had swallowed a capsule of carrot powder displayed “laughter-face” expressions (like little in-utero smiles), while those exposed to kale powder showed more “cry-face” or grimace-like movements.
Your babies can sense different flavors and even flash a tiny smile while still in the womb. Thanks to their developing taste buds and senses, they’re already little food critics before their very first meal.
Why do babies smile?
Research shows that smiling isn’t just a milestone, it’s a dialogue. Developmental scientists, Daniel Messinger and Alan Fogel describe how babies use smiles interactively, shaping them in response to your expressions.
In other words, your baby’s smile is not random: it’s their very first way of joining the conversation with you, long before words arrive.
It also signals that the baby’s brain is growing and learning how to connect with you. Smiles release oxytocin and endorphins in both baby and parent, a feedback loop of joy and bonding.
The evolutionary power of smiles
Anthropologists believe smiles are not only cute, but also ancient. They note that baby monkeys and chimpanzees smile in their sleep, just like human newborns. It shows that smiling has been around for at least 30 million years, long before humans existed.
The social smile is our superpower. While many primates grin, humans are special because we use smiling as a true social signal. A baby’s grin doesn’t just happen, it’s meant to connect, invite closeness, and build trust.
Moreover, nature made babies irresistible. Big eyes, soft cheeks, that sweet baby smell and of course, the smile are all part of an evolutionary design. They’re nature’s way of making sure parents and caregivers can’t resist staying close and giving protection.
When do babies smile at you?
Often, around 6–12 weeks, you’ll see that heart-melting social smile directed at you. Their vision is sharpening, so your face goes from being a blur to their favorite sight.
By around 4 months, babies don’t just smile randomly. Studies show that they wait for the perfect moment to grin, knowing it will make you smile back and strengthen your bond.
How can parents encourage baby smiles?
While social smiles typically appear around 6 – 12 weeks, parents can encourage these joyful milestones with a few simple, loving actions.
1. Make eye contact and share gentle tones
Babies are naturally drawn to faces, especially yours. Making eye contact while talking or singing in a soft, rhythmic voice helps your baby feel secure and engaged. Those soothing tones can spark the first intentional grins as your baby learns to recognize and respond to you.
2. Play with expressions
Don’t be afraid to be a little silly. Babies love exaggerated facial expressions like wide smiles, raised eyebrows, or playful pouts. These big cues are easier for developing eyes to track and often elicit those magical first smiles.
3. Classic peek-a-boo
This timeless game works because it combines surprise, rhythm, and connection. Cover your face briefly, then reveal it with a big smile. Your baby learns to anticipate the fun, and soon enough, the giggles follow.
4. Gentle touch and tickle moments
Soft tickles on your baby’s belly, feet, or under the chin can trigger reflexive chuckles that gradually become real laughter. The key is to keep it gentle and playful, never overwhelming.
5. Mirror smiles back
Babies are brilliant mimics. When you smile at them, they’re more likely to return the gesture. In fact, studies show that parents smile about 30% more once they have a baby where each smile fuels another.
Does music have an impact on babies’ smiles?
In a study published in Frontiers in Psychology, infants showed a clear preference for infant-directed speech: those happy, high-pitched, expressive tones that sound more musical than regular talk. In fact, when voices or songs evoke joy, babies are more responsive and likely to smile. This holds true even when distinguishing between spoken and sung content.
So, don’t hesitate to sing, hum, or play calming music. Babies are natural fans of rhythm and melody.
Smile storms: Why do babies grin in their sleep?
Many newborns have bursts of grins during REM sleep, nicknamed “smile storms.” The infants spend nearly half of their sleep in REM (Rapid Eye Movement) sleep, a stage where the brain is surprisingly active. It’s in these dreamy moments that their facial muscles twitch and expressive movements like smiles happen.
Parents see it as a window into baby dreams.
When do babies laugh?
It’s a journey worth the wait. After the charming reflex and social smiles, your little one may begin giggling around 3 to 4 months.
By 4 to 6 months, you might hear the first genuine, full-bodied laugh and oh, what music that is! These laugh moments aren’t random; they mark growing control over movements, blossoming emotional depth, and a love language before any words form.
If you’d love to know more about those sweet belly laughs, read When do babies start laughing? The science behind baby giggles.
When to check with your pediatrician?
If your baby isn’t smiling by 2 months, it may still be normal especially for preemies. By 2 months, most full-term infants begin smiling purposefully. But, if you haven’t noticed one by 3 months, it’s a good idea to mention it at your pediatrician visit just to double-check.
Above all, remember that every baby blooms on their own timeline.
Conclusion
Tiny reflex smirks in sleep, ultrasound smiles before birth, the first social grin, and those contagious giggles, each marks a new chapter in your baby’s story. Science explains them as brain growth, bonding hormones, and evolution at work. But to parents, they are so much more: living proof that love flows both ways. That very first smile is indescribable: beyond words, beyond measure, and forever etched in memory.
Sources:
- The baby’s first smile. AAP. “When Do Babies First Smile?”
- Babies smiling in the womb .Association of Psychological Science. “Flavor Sensing in Utero and Emerging Discriminative Behaviors in the Human Fetus”
- Baby’s smile is a dialogue. Developmental Scientists – Daniel Messinger and Alan Fogel. “The Interactive Development of Social Smiling”
- Evolution of smile. CARTA. “Smiling”
- Smile is a part of evolutionary design. University of Oxford. “Babies Don’t Just Look Cute, Scientists Find”
- Purpose of baby smile. PLOS ONE. “Babies Time Their Smiles to Make Their Moms Smile in Return”
- Impact of music on baby smiles. Frontiers in Psychology. “Speech vs. singing: infants choose happier sounds”
- Babies smiling during sleep. NCBI. “A video polysomnographic study of spontaneous smiling during sleep in newborns”
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