Newborns take their first breath within seconds of birth, triggered by a dramatic shift from fluid-filled lungs to air breathing. A healthy newborn breathes 40 to 60 times per minute, roughly two to three times faster than an adult. This rapid rate compensates for lungs that are still maturing and a chest wall that doesn’t yet work as efficiently as it will later in life.
What Happens During the First Breath
Before birth, a baby’s lungs are filled with fluid rather than air. Oxygen comes entirely from the placenta through the umbilical cord. The transition to breathing air requires two things to happen almost simultaneously: the lung fluid needs to clear out, and the baby needs to start pulling air in.
During labor, a surge of adrenaline (epinephrine) in the baby’s bloodstream activates sodium channels in the lung tissue. These channels pull sodium across the lung lining, and water follows. Most of this fluid passes directly into the tiny blood vessels surrounding the lungs rather than draining through lymph vessels, which only handle a small fraction. This is why labor itself matters for the transition. Babies delivered by cesarean section before labor begins tend to clear lung fluid more slowly, since they miss the hormonal surge that kicks the process into gear.
Once fluid begins clearing, the baby’s first cry or gasp creates negative pressure inside the chest, drawing air into the lungs for the first time. This initial breath requires significantly more effort than any breath that follows, because the tiny air sacs in the lungs have never been inflated before.
How Surfactant Keeps the Lungs Open
Air sacs in the lungs are incredibly small, and the surface tension of the thin liquid lining them would cause them to collapse after every breath if not for a substance called surfactant. Surfactant is a mixture of fats and proteins that coats the inside of each air sac, dramatically lowering surface tension so the sacs stay partially open between breaths. Without it, a baby would have to exert enormous effort with every single breath, essentially re-inflating collapsed lungs each time.
Surfactant production ramps up in the final weeks of pregnancy. Premature babies often don’t have enough of it, which is a major reason they develop respiratory distress syndrome, one of the most common breathing problems in preterm infants.
Why Newborns Breathe Through Their Noses
Newborns strongly prefer breathing through their noses rather than their mouths, though they aren’t strictly locked into it. In a newborn’s resting position, the soft palate sits right against the tongue, effectively sealing off the mouth as an airway. If the nose becomes blocked, babies can switch to mouth breathing, but it takes time. Studies measuring this response found that it takes an average of about 8 seconds for a newborn to open the mouth airway after nasal blockage, with some babies taking as long as 32 seconds. Older and awake babies switch faster than younger or sleeping ones.
This nasal preference exists partly because of the baby’s anatomy. A newborn’s voice box sits much higher in the throat than an adult’s, at the level of the first through third cervical vertebrae compared to the sixth and seventh in adults. This high position helps keep the airway protected during feeding, allowing babies to swallow and breathe in close sequence, but it also means the mouth route for air is less readily available.
A Flexible Chest Wall Has Trade-Offs
A newborn’s ribs are made largely of cartilage rather than the harder bone found in adults. This makes the chest wall about three times more flexible than the lungs themselves. That flexibility is essential at birth because it allows the chest to expand as lung fluid is absorbed into the surrounding tissue. But it comes with a cost.
Because the chest wall is so pliable, it doesn’t hold its shape well against the natural tendency of the lungs to deflate. In adults, stiffer ribs help keep the lungs partially inflated even at rest. Newborns lack this support, so their resting lung volume is lower, holding only about 10 to 15 percent of total lung capacity right after birth compared to 30 to 35 percent in adults. By one day old, that number improves to 20 to 25 percent as the lungs continue to adapt.
This floppy chest wall also explains why you can sometimes see the skin between a newborn’s ribs pulling inward with each breath. In mild cases this is normal. When it becomes pronounced, with deep indentations between or below the ribs, it signals that the baby is working too hard to breathe.
How Breathing Stays Regulated
Newborns rely heavily on a built-in safety mechanism called the Hering-Breuer reflex. Stretch receptors in the lungs detect when they’ve expanded enough during a breath and send a signal through the vagus nerve to the brainstem, which then stops the inhale and triggers an exhale. This reflex is much more active in newborns and preterm infants than in adults, helping to stabilize their breathing pattern on a breath-by-breath basis and preventing the lungs from over-inflating.
Despite this regulation, newborn breathing often looks irregular. Periodic breathing is a common pattern in which a baby takes several quick breaths, pauses for 5 to 10 seconds, then starts breathing again on their own. This is normal and reflects an immature respiratory control system that is still fine-tuning itself. A pause lasting longer than 10 seconds, skin that turns bluish, or difficulty waking the baby are signs that something more serious may be happening.
Signs of Breathing Trouble
Because newborn breathing is naturally fast and sometimes irregular, it helps to know what actual distress looks like. The key warning signs are:
- Nasal flaring: the nostrils spread wide with each breath, indicating the baby is trying to pull in more air
- Grunting: a small sound at the end of each exhale, which the baby produces instinctively to keep air sacs from collapsing
- Retractions: visible pulling of the skin inward between the ribs, below the rib cage, or at the base of the throat
- Fast, shallow breathing: rates consistently above 60 breaths per minute at rest
- Color changes: a bluish tint around the lips or skin
Any of these signs, especially in combination, indicate the baby is working harder than normal to get enough oxygen. Premature infants are at higher risk because of lower surfactant levels and an even more compliant chest wall, but respiratory distress can occur in full-term babies as well.