Babies are born with sinuses, but not the full set that adults have. At birth, two of the four pairs of paranasal sinuses are already present at an appreciable size: the ethmoid sinuses (between the eyes) and the maxillary sinuses (in the cheekbones). The other two pairs, the sphenoid and frontal sinuses, are barely sketched out at birth and don’t meaningfully develop until months or years later. This staggered growth pattern means that the infant face is not just a miniature version of an adult face; its internal architecture is genuinely different, and that has real consequences for how babies experience congestion, when they can get true sinus infections, and how those infections behave.
Which Sinuses Are Present at Birth
All four pairs of paranasal sinuses begin forming during the third and fourth months of fetal life, starting as tiny outpouchings from the nasal lining. But the timing of their expansion varies dramatically. By the time a baby is born, the ethmoidal labyrinth and the maxillary sinuses have reached a size that matters anatomically, while the sphenoid and frontal sinuses exist only as rudimentary precursors with little functional space.1PubMed. Nasal cavities and paranasal sinuses in newborns and children
The ethmoidal sinuses sit in the bone between the eye sockets. In newborns, these are the most clinically relevant sinuses because they are the only ones developed enough to become meaningfully infected in the first weeks of life. The maxillary sinuses, tucked beneath each cheek, are present but still small compared to what they will become. Their major expansion happens after birth, driven by the growth of the facial bones and the eruption of teeth.1PubMed. Nasal cavities and paranasal sinuses in newborns and children
If you’ve ever wondered why a baby’s face looks so flat compared to an adult’s, the underdeveloped sinuses are part of the story. The sinuses literally hollow out the facial bones over time, and much of that remodeling hasn’t happened yet at birth. The maxillary sinuses won’t reach their full adult dimensions until the late teens, when the permanent teeth have fully come in and the midface has finished growing.
When the Sphenoid Sinus Appears
The sphenoid sinus sits deep in the skull, behind the nose and just below the brain. At birth it is essentially a solid bone with no air space to speak of. The process of hollowing out, called pneumatization, starts surprisingly early in some children. Imaging research has detected a pneumatized sphenoid sinus as early as two months of age, though this varies from child to child.2American Journal of Rhinology. Pneumatization of the Sphenoid Sinus in Children Evaluated by Magnetic Resonance Imaging
Growth accelerates between the ages of one and two, then continues steadily through childhood. By around age three to four, most children show clear pneumatization of at least the front portion of the sphenoid bone. By age ten, pneumatization is typically complete.3PubMed. The sphenoid sinus during childhood: establishment of normal developmental standards by MRI The sinus doesn’t reach adult-like dimensions until after age twelve, at which point it tends to plateau.4PubMed. Development of the sphenoid sinus from newborn to age 18: A computed tomography imaging analysis
There is some disagreement between studies about exactly when pneumatization begins and finishes, partly because different imaging techniques and measurement criteria produce different timelines. MRI-based studies and CT-based studies sometimes give slightly different windows, but the broad trajectory is consistent: the sphenoid sinus transforms from a solid bone into a meaningful air cavity during early childhood, with the process stretching into adolescence before it is truly complete.
The Frontal Sinuses Come Last
The frontal sinuses, the ones behind your forehead, are the last to show up and the most variable between individuals. They form when the outer layer of the frontal bone begins separating from the inner layer, creating an air pocket in between.5Wiley Online Library (The Anatomical Record). Frontal Sinus Development and Juvenile Age Estimation This process doesn’t really get going until around age six to eight, and the sinuses continue growing well into the late teens.
What makes the frontal sinuses unusual is the degree of individual variation. Some adults develop large, well-defined frontal sinuses. Others develop very small ones. And a small percentage never develop them at all. Studies using CT imaging have found bilateral frontal sinus absence (meaning neither side develops) in roughly one to four percent of people, depending on the population studied. Unilateral absence, where only one side fails to develop, is slightly more common.6PubMed Central. Aplasia and Agenesis of the Frontal Sinus in Turkish Individuals: A Retrospective Study Using Dental Volumetric Tomography7PubMed Central. Frequency of the frontal sinus aplasia among Saudi Arabian population
Women tend to have higher rates of frontal sinus absence than men, and the right side is more commonly absent than the left when only one side is missing. This variability is interesting to forensic scientists because frontal sinus shape is as unique as a fingerprint, making it useful for identification. But the frequency of absent sinuses depends heavily on how researchers define “present,” which makes comparing studies tricky. CT-based definitions tend to produce lower absence rates than older X-ray-based methods.8PubMed. Revisiting global patterns of frontal sinus aplasia utilizing computed tomography
What Sinuses Actually Do
There’s a surprisingly old debate about why we even have paranasal sinuses. Proposals over the years have included lightening the skull, adding resonance to the voice, insulating the brain, and absorbing shock during facial trauma. None of these explanations has held up well under scrutiny. The sinuses don’t weigh enough to meaningfully lighten the skull; the voice-resonance idea has been studied and largely dismissed; and there’s no strong evidence they protect the brain from impact.
A more compelling explanation emerged with the discovery that healthy sinus lining continuously produces nitric oxide, a gas with potent antimicrobial and vasodilating properties. The epithelium in the sinuses expresses an enzyme that generates large amounts of nitric oxide, which then flows into the nasal passages with each breath.9The Anatomical Record. Nitric Oxide and the Paranasal Sinuses This nitric oxide appears to directly inhibit the growth of bacteria and viruses while also stimulating the tiny hair-like structures (cilia) that sweep mucus and trapped debris out of the nasal cavity.10PubMed. Why do we have paranasal sinuses?
In practical terms, the sinuses seem to function primarily as an extension of the nasal defense system, producing a chemical that helps keep the airways clean. For babies, whose immune systems are still maturing, this means the sinuses they do have at birth are already contributing to their ability to fight off respiratory infections, even though the full sinus system won’t be online for years.
Can Babies Get Sinus Infections
Yes, though the pattern is different from what adults experience. Because newborns have only ethmoidal and small maxillary sinuses, those are the ones that can become infected. Frontal sinusitis is physically impossible in a baby because the frontal sinuses don’t exist yet, and sphenoid sinusitis is extremely rare before age three or four.
Ethmoid sinusitis in a very young infant can be serious. There is a documented case of a five-week-old boy who developed periorbital cellulitis, a spreading infection around the eye, that was traced back to acute ethmoiditis on CT imaging. The authors believed this was the youngest confirmed case of periorbital cellulitis caused by sinus infection.11PubMed Central. Periorbital cellulitis secondary to ethmoiditis in a 5-week-old child The case underscores something worth knowing: when a very young baby develops swelling and redness around the eye, an underlying sinus infection should be considered even though the sinuses are small.
In older infants and toddlers, the question parents most often face is whether their child’s stuffy nose is a garden-variety cold or a bacterial sinus infection. Most of the time it is a cold. Acute rhinosinusitis is overwhelmingly triggered by viral infection, and only a small fraction of cases go on to develop a true bacterial component. The symptoms of viral and bacterial sinus infections overlap substantially, and telling them apart relies on the pattern and duration of symptoms rather than on any single test.10PubMed. Why do we have paranasal sinuses?
The American Academy of Pediatrics recommends against using imaging to distinguish a bacterial sinus infection from a viral upper respiratory infection in children aged one to eighteen. Plain X-rays, CT scans, and MRIs are not helpful in this situation because the lining of the sinuses swells up during a common cold, making the images look abnormal even when there’s no bacterial infection.12Pediatrics. Clinical Practice Guideline for the Diagnosis and Management of Acute Bacterial Sinusitis in Children Aged 1 to 18 Years Diagnosis is clinical, based on symptoms lasting longer than ten days without improvement, or symptoms that seem to be getting better and then suddenly worsen.
How Adenoids Complicate the Picture
Adenoids are pads of lymphoid tissue that sit at the back of the nasal cavity, right next to the openings where the sinuses drain. In children, the adenoids can grow quite large, and their location means they can physically block sinus drainage or serve as a reservoir for bacteria. Research has found that biofilms, sticky colonies of bacteria that resist antibiotics, can form on the surface of enlarged adenoids. These biofilms may continuously reseed the sinuses with bacteria, making chronic sinus infections in children difficult to treat with antibiotics alone.13PubMed. Identification of adenoid biofilms in chronic rhinosinusitis
This is why adenoidectomy, surgical removal of the adenoids, is often the first step when a child has chronic sinusitis that hasn’t responded to medication. The physical removal of the adenoid tissue eliminates the biofilm reservoir. Studies have shown that adenoidectomy relieves chronic sinusitis symptoms in the majority of children, and follow-up research has documented a reduction in harmful bacteria and an increase in normal bacterial communities in the nasopharynx after the procedure.14PubMed. Efficacy of adenoidectomy in relieving symptoms of chronic sinusitis in children15PubMed Central. Evaluation of Children with Chronic Rhinosinusitis after Adenotonsillectomy
For parents, the takeaway is that a child who seems to have one sinus infection after another may not actually be failing to clear individual infections. The problem may be that bacteria living on the adenoids keep reinfecting the sinuses. This is a different problem than a child who gets occasional, self-resolving sinus infections, and it calls for a different approach.
Balloon Sinuplasty in Children
When chronic sinusitis in children doesn’t respond to medication or adenoidectomy, endoscopic sinus surgery has traditionally been the next step. Over the past fifteen years, balloon catheter dilation, often called balloon sinuplasty, has emerged as a less invasive alternative for pediatric patients. The procedure involves threading a small balloon into the blocked sinus opening and inflating it to widen the passage, without cutting tissue.
Early feasibility studies found the procedure successful in about ninety percent of treated sinuses in children, with the main failures occurring in underdeveloped (hypoplastic) maxillary sinuses, which were too small for the balloon catheter.16PubMed. Safety and feasibility of balloon sinuplasty for treatment of chronic rhinosinusitis in children A later multicenter study treated children aged two and older and reported significant improvement in quality-of-life scores at six months, with over ninety percent of patients improving by a clinically meaningful amount. All dilation attempts in that study were successful, with no complications.17International Forum of Allergy & Rhinology. Prospective, multicenter evaluation of balloon sinus dilation for treatment of pediatric chronic rhinosinusitis
A systematic review of balloon sinuplasty in children found that the available evidence consistently points to safety and effectiveness, with low surgical revision rates and most children not needing further antibiotic courses for sinusitis during follow-up periods of up to a year.18Journal of Otolaryngology – Head & Neck Surgery. Efficacy and safety of paranasal sinus balloon catheter dilation in pediatric chronic rhinosinusitis: A systematic review The procedure is not appropriate for every child. It works best in children whose sinuses are developed enough to accept the catheter, which brings the developmental timeline full circle: a surgeon needs to know how far along a child’s sinuses are before deciding what kind of intervention makes sense.
Dealing with Baby Congestion When Sinuses Are Not the Problem
Most of the time, a stuffy-sounding baby does not have a sinus infection. Newborn nasal passages are simply narrow, and even a small amount of mucus can make breathing sound congested. Parents often describe their newborn as “snorting” or “rattling” during feeding or sleep, which is almost always normal anatomy rather than disease.
When babies and toddlers do catch a cold, the options for relief are limited compared to what adults can use. Decongestant medications and antihistamines are not recommended for children under about four to six years old due to safety concerns and a lack of evidence that they work in this age group. Saline nasal drops or spray remain the go-to recommendation. A randomized trial of seawater-based nasal spray in infants and toddlers with the common cold found that children who used the spray experienced faster relief from nasal congestion, with immediate improvement within five to fifteen minutes of application, and a higher recovery rate by day ten compared to standard care alone. No adverse events were linked to the spray.19SpringerLink / European Archives of Oto-Rhino-Laryngology. Efficacy and safety of seawater-based nasal irrigation on nasal congestion in infants and toddlers with common cold: a randomized controlled trial
Bulb syringes and nasal aspirators can help clear mucus that a baby can’t blow out on their own, especially before feeding and sleep. Keeping the air humidified and offering extra fluids during a cold are standard recommendations. The key thing to watch for is any sign that congestion is more than a cold: persistent symptoms beyond ten days without improvement, high fever alongside nasal discharge, swelling or redness around the eyes, or a baby who seems significantly more ill than a typical cold would explain. Those red flags warrant a call to the pediatrician rather than more saline drops.
How Sinus Growth Relates to Other Skull Air Spaces
The paranasal sinuses are not the only hollow air spaces in the skull. The mastoid air cells, located in the bone behind the ear, also undergo pneumatization during childhood, and researchers have been curious about whether the two systems develop in tandem. Studies using three-dimensional CT reconstruction have found that both systems expand with age and that women tend to have smaller volumes overall.20PubMed Central. Morphometric examination of the paranasal sinuses and mastoid air cells using computed tomography
There appears to be a positive correlation between mastoid air cell volume and sphenoid sinus volume, suggesting that some shared biological process influences how aggressively bone is hollowed out during growth. However, the mastoid cells and the maxillary sinuses don’t seem to track each other as closely.21PubMed. Comparative study of the pneumatization of the mastoid air cells and paranasal sinuses using three-dimensional reconstruction of computed tomography scans When researchers controlled for age, the direct relationship between mastoid and sinus volumes weakened, meaning that much of the apparent correlation was simply both systems getting bigger as the child grew.22PubMed. Three-dimensional morphometric analysis of paranasal sinuses and mastoid air cell system using computed tomography in pediatric population
From a clinical standpoint, a child with unusually underdeveloped sinuses may or may not have underdeveloped mastoid air cells. The two systems share the same general growth trajectory, age being the dominant factor, but they aren’t locked together in a one-to-one relationship. This matters for surgeons who operate near either structure, because assumptions about sinus size based on mastoid anatomy, or vice versa, can be unreliable in individual patients.