The paranasal sinuses are air-filled cavities located within the bones of the skull and face, serving to lighten the skull, humidify air, and enhance voice resonance. The direct answer is that while babies are born with the beginnings of some sinuses, these air pockets are far from the size and shape seen in adults. The process of sinus development is a gradual one, stretching from gestation through adolescence, and this immaturity has important implications for common infant health issues like congestion.
The Sinuses Present at Birth
At birth, a baby’s skull contains two pairs of sinuses. The maxillary sinuses, located in the cheekbones, are the earliest to develop, beginning during the third gestational month. At birth, the maxillary sinus is a tiny air-filled space.
The ethmoid sinuses are the other set present at birth, positioned between the eyes and near the bridge of the nose. These sinuses are composed of small, rudimentary, honeycomb-like air cells. The remaining two pairs—the frontal sinuses in the forehead and the sphenoid sinuses deep within the skull—are not yet developed as air-filled cavities. They exist instead as unpneumatized bone or tiny, marrow-filled spaces.
Timeline of Sinus Development
The process of the sinuses growing and becoming air-filled is known as pneumatization, and it is closely tied to the growth of the facial bones after birth. The maxillary and ethmoid sinuses continue their slow expansion throughout early childhood. The ethmoid sinuses reach their full adult size around 12 to 14 years of age, and the maxillary sinuses continue to enlarge until the end of puberty.
The sphenoid sinuses, located behind the nose and deep in the skull, are the next to begin significant pneumatization, starting around two to three years of age. The last pair to develop are the frontal sinuses in the forehead, which often do not become visible until a child is between six and eight years old. Growth of the frontal sinuses continues until the end of puberty, meaning the entire sinus system does not reach full maturity until late adolescence or early adulthood.
Why Babies Get Stuffy (And Why True Sinusitis is Rare)
The common “stuffy nose” experienced by infants is usually a result of inflammation in the nasal passages (rhinitis) rather than an infection within the sinuses (sinusitis). A baby’s nasal passages are exceptionally small and narrow, meaning even a minor amount of swelling from a cold or viral infection can lead to significant obstruction and the characteristic congested sound. The presence of dried mucus, lingering amniotic fluid, or exposure to irritants like dry air can also create this noisy breathing.
Because the maxillary and ethmoid sinuses are so tiny and the frontal and sphenoid sinuses are absent or unformed, it is physiologically difficult for a true bacterial sinus infection to occur in infants. The small volume of the existing sinuses means that while inflammation can happen, the necessary conditions for a full-blown bacterial infection are less frequently met than in older children or adults. While about 90% of sinus issues begin with a viral upper respiratory infection, only a small percentage of these cases progress to a bacterial sinusitis in children. This immaturity of the sinus structure provides protection against the chronic or severe sinus infections that affect older populations.