Babies laugh because something surprises them in a way they can make sense of. That’s the short answer, but the full picture involves a fascinating mix of brain development, social bonding, and a growing understanding of how the world is supposed to work. Most babies produce their first real laugh between four and six months of age, and from that point on, the things that make them laugh evolve rapidly as their brains mature.
When Laughter First Appears
Newborns smile within their first few weeks, but those early grins are reflexes, not responses to anything funny. By about eight weeks, babies begin showing social smiles, reacting to faces and voices around them. True laughter, the kind with sound and clear delight, typically arrives between four and six months. At this stage, physical stimulation is the easiest trigger. Gentle tickling, bouncing, or being swooped through the air will get a giggle before any game or joke will.
As babies approach six and seven months, the balance shifts. They start laughing more at things they see and hear rather than things they feel. A parent putting a cup on their head or pretending to sneeze becomes funnier than a tickle on the belly. This shift reflects something important happening in the brain: the baby is building expectations about how objects and people normally behave, and violations of those expectations become funny.
Why Surprises Are Funny (But Only the Right Kind)
The core mechanism behind baby laughter is the same one that drives adult humor: incongruity. Something happens that doesn’t match what the brain expected. For a baby, this could be as simple as a parent hiding behind their hands and then reappearing, or a stuffed cat making a “woof” sound instead of a meow. The baby’s brain registers a mismatch between what it predicted and what actually happened.
But here’s the key distinction researchers have identified. Not all surprises are funny. When babies encounter something truly inexplicable, like a magic trick where an object seems to vanish, they tend to stare with stunned expressions rather than laugh. They can’t make sense of what happened, so the surprise produces confusion instead of delight. Laughter happens when the surprise is resolvable, when there’s enough context for the baby to figure out that the situation is safe and playful rather than genuinely strange. A parent’s silly face is surprising but clearly not threatening. A toy disappearing into thin air is surprising and unsettling.
People are central to this equation. When another person is part of the surprising event, babies are far more likely to laugh than when they witness the same kind of incongruity from an object alone. The presence of a familiar caregiver who is clearly enjoying the moment gives the baby permission, in a sense, to react with joy rather than alarm.
The Games That Work Best
A large survey of 390 parents conducted by researchers at Goldsmiths, University of London, found that peekaboo is the single most reliable way to make a baby laugh. About 70% of babies laughed out loud at peekaboo, and parents rated it nearly twice as funny as any other game tested. Other effective triggers included putting a cup on your head, stuffing a cloth in your mouth, tearing paper, and making a toy animal produce the wrong sound.
What these games share is a pattern: something familiar behaves in an unfamiliar way, delivered by a person the baby trusts. The cup belongs on a table, not on Dad’s head. Mom’s face was there, then gone, then back. The predictability of the setup combined with the silliness of the payoff creates the perfect conditions for laughter.
Sound plays a big role too. Babies are drawn to exaggerated vocal patterns, and certain noises reliably produce giggles. Blowing raspberries, tongue clicking, and funny vocal effects all work because they’re unexpected mouth sounds delivered with playful energy. Babies as young as four or five months begin experimenting with these sounds themselves, partly because they notice how much their own raspberry-blowing makes the adults around them laugh and engage, which creates a rewarding feedback loop.
Why Your Reaction Matters
A baby’s laughter isn’t purely a solo experience. Research tracking infants at five, six, and seven months found that parental emotion significantly shapes how much a baby laughs. When parents performed an absurd action (like putting a book on their head) with a big smile and exaggerated amusement, babies laughed more often, laughed sooner, and laughed for longer compared to when parents did the exact same action with a neutral expression.
This effect grows stronger with age. Five- and six-month-olds will smile and laugh at something absurd even when a parent keeps a straight face, though they laugh longer when the parent joins in. By seven months, babies become more dependent on the parent’s emotional cue. Without it, they laugh significantly less. This suggests that as babies get older, they increasingly look to the people around them to help interpret whether something is funny, a process researchers call social referencing. The caregiver’s face becomes a kind of emotional guide: if you’re laughing, this must be safe and fun.
The Biology Behind the Giggles
Laughter triggers the release of endorphins, the brain’s natural feel-good chemicals. This is the same system that makes physical touch and grooming feel rewarding in primates, and it plays a direct role in social bonding. When a baby laughs and a parent laughs back, both brains are flooding with chemicals that reinforce the connection between them.
On the parent’s side, hearing a baby laugh activates oxytocin pathways that reduce anxiety and increase feelings of closeness. Oxytocin quiets the brain’s threat-detection center, making parents less reactive to stress and more attuned to their baby’s signals. At the same time, it increases the brain’s reward response to the baby’s laughter, making the sound feel genuinely pleasurable. This creates a neurochemical incentive for parents to keep playing, keep being silly, and keep engaging, which is exactly what the baby needs for healthy development.
From an evolutionary perspective, this system likely developed because early humans needed efficient ways to bond in groups. Physical grooming, the primary bonding method for other primates, is slow and requires one-on-one contact. Laughter can happen in groups, doesn’t require physical touch, and triggers the same bonding chemistry. Babies who could laugh, and whose laughter made caregivers want to stay close, had a survival advantage.
How Humor Changes in the First Year
The things that make a baby laugh at four months are very different from what works at twelve months, because humor tracks directly with cognitive development. In the early months, physical sensations dominate: tickling, bouncing, funny sounds. These work because they don’t require the baby to have any expectations about how the world works. The sensation itself is the surprise.
By six months, babies have learned enough about everyday objects to find their misuse hilarious. They know a cloth goes on the table, so watching someone stuff it in their mouth is a violation of a rule they’ve just figured out. By eight to ten months, babies start creating their own humor. They’ll offer you a toy and then pull it back, or make a sound they know is silly, watching your face carefully for a reaction. They’re not just responding to jokes anymore. They’re telling them.
Around twelve months, the humor becomes even more social and intentional. Babies will repeat actions that got a laugh, vary them to test what’s funnier, and look to different people to see if the joke lands with a new audience. This is sophisticated cognitive work: understanding other people’s perspectives, predicting their reactions, and adjusting behavior based on feedback. What looks like a simple giggle is actually one of the earliest signs of social intelligence at work.