Most babies who sleep with their mouths open are doing so because something is blocking their nose, not because of a habit you need to break. The fix isn’t about mechanically closing your baby’s mouth. It’s about figuring out why the mouth is open in the first place and addressing that cause. In almost all cases, clearing the nasal airway solves the problem.
Why Babies Sleep With Their Mouths Open
Newborns are obligate nasal breathers, meaning they strongly prefer breathing through their noses and will only switch to mouth breathing when the nasal airway is compromised. So an open mouth during sleep is a signal, not just a quirk. The most common culprit is simple congestion from a cold, dry air, or allergic irritation. Allergic rhinitis alone affects roughly 40% of children in the United States, causing swelling of the nasal lining and excess mucus that can partially or fully block airflow.
Beyond everyday congestion, enlarged adenoids or tonsils are a major cause, especially after the newborn period. These tissues sit at the back of the nose and throat and can physically narrow the airway. Less common but worth knowing about: a tongue tie (ankyloglossia) can also play a role. Research comparing newborns with and without tongue tie found that babies with a restricted lingual frenulum tend to rest with their lips parted and their tongue sitting low in the mouth, while babies without it naturally keep their lips closed and tongue elevated at rest.
Rare structural causes include a deviated nasal septum, narrowed nasal passages (choanal stenosis), or conditions like Pierre Robin syndrome. These are typically identified shortly after birth.
Why It Matters Beyond One Night
Occasional mouth breathing during a cold is not a concern. Chronic mouth breathing over months or years, however, can genuinely affect how your child’s face and jaw develop. Children who habitually breathe through their mouths are more likely to develop a narrow upper jaw, a high-arched palate (11% higher in the molar region compared to nasal breathers), and bite problems like anterior open bite, posterior crossbite, and increased overjet. The lower jaw tends to rotate downward and backward, which can lengthen the face over time.
These changes happen because the tongue’s resting position shapes the palate during growth. When a child breathes through the nose, the tongue naturally presses against the roof of the mouth, providing gentle outward pressure that helps the upper jaw widen properly. Mouth breathing drops the tongue low, removing that support. Animal studies that artificially blocked nasal breathing confirmed the same pattern: the jaw shifted, the face lengthened, and the bite changed. So while there’s no need to panic over a stuffy nose, persistent mouth breathing is worth resolving sooner rather than later.
Clear the Nose Before Bed
The single most effective thing you can do is make sure your baby’s nasal passages are open at bedtime. Here’s the recommended approach from Cincinnati Children’s Hospital:
- Use saline drops first. Place three to four drops of normal saline solution into one nostril using a nose dropper. Hold your baby in position for about a minute to let the saline thin the mucus.
- Suction with a bulb syringe. Squeeze all the air out of the bulb before placing the tip gently into the nostril until it seals. Slowly release your thumb to let suction pull the mucus out. Squeeze the contents into a tissue and repeat on the other side.
- Repeat if needed. You may need to suction each nostril several times to fully clear it.
Always suction before feedings or bedtime, not after eating. Doing it after a feed can cause spitting up. If your baby fights the bulb syringe, a battery-powered nasal aspirator or parent-powered suction device (like a NoseFrida) can be easier to use and more effective for thick mucus.
Get the Room Humidity Right
Dry air swells nasal tissue and thickens mucus, which is why mouth breathing often worsens in winter or in air-conditioned rooms. Boston Children’s Hospital recommends keeping indoor humidity between 35 and 50 percent. Below that range, babies are more likely to develop dry nasal passages, nosebleeds, and difficulty breathing. Above 50 percent encourages mold and dust mites, which create their own set of problems.
A cool-mist humidifier in the nursery is the simplest fix. Place it near but not directly next to the crib, and clean it regularly to prevent bacterial buildup. A basic hygrometer (under $10 at most hardware stores) lets you monitor the level so you’re not guessing.
What About Pacifiers?
Pacifiers may actually help. A study testing newborns’ ability to breathe through their mouths during nasal blockage found that babies with a pacifier in place handled the situation significantly better. Without a pacifier, 17 out of 20 infants showed signs of upper airway obstruction during 62% of tests. With a pacifier, only 10 out of 20 showed those signs, and only during 30% of tests. The pacifier appears to help stabilize the tongue and jaw in a position that keeps the oral airway more open and functional.
This doesn’t mean a pacifier will close your baby’s mouth, but if your baby already uses one, it may support better breathing mechanics during sleep. Follow standard guidelines on pacifier sizing and replacement.
Never Use Mouth Tape on a Baby
Mouth taping has gained popularity on social media as a sleep hack for adults, but it is dangerous for infants and young children. Babies cannot remove tape themselves, and if their nasal airway becomes blocked for any reason (a sudden increase in mucus, a shift in position), they need the mouth as a backup breathing route. Taping it shut removes that safety valve entirely. There is no medical evidence supporting mouth taping even in adults, and applying it to a baby creates a suffocation risk.
Similarly, chin straps, headbands, or any device designed to hold the jaw closed have no place in infant sleep. These are not safe at any age in infancy.
Other Practical Steps
Keep your baby’s sleep environment free of common allergens. Wash crib sheets weekly in hot water, vacuum the nursery regularly, and keep pets out of the room if your baby shows signs of allergic congestion. Dust mites and pet dander are among the most frequent triggers of nasal swelling in infants.
If your baby has reflux, stomach acid can irritate the nasal passages from behind, causing swelling that mimics a cold. Managing reflux with your pediatrician can sometimes resolve unexplained nasal congestion.
One thing that doesn’t help: elevating the head of the crib. The American Academy of Pediatrics recommends that babies sleep flat on their backs on a firm surface, even when congested. Inclined sleep surfaces increase the risk of suffocation and positional airway obstruction, which is the opposite of what you want.
Signs That Point to a Bigger Problem
Mouth breathing that persists even when your baby isn’t sick deserves medical attention. Watch for snoring on most nights, pauses in breathing, gasping or choking sounds, restless sleep with frequent position changes, and nighttime sweating. These are hallmarks of pediatric obstructive sleep apnea, most often caused by enlarged adenoids or tonsils. Notably, infants and young children with sleep apnea don’t always snore; sometimes the only sign is chronically disturbed sleep.
Pediatric ENT referral guidelines recommend evaluation when a child has persistent nasal obstruction despite medical treatment, or when snoring is accompanied by difficulty breathing, symptoms consistent with apnea, or poor sleep quality. If your baby also has feeding difficulties, poor weight gain, or episodes of color change (turning pale or bluish), those warrant prompt evaluation. A pediatric ear, nose, and throat specialist can assess whether the adenoids or tonsils are the problem and whether intervention is needed.
If you suspect tongue tie, a lactation consultant or pediatric dentist experienced with oral restrictions can evaluate the frenulum. Babies with tongue tie often also have difficulty latching during breastfeeding, a clicking sound while feeding, or a heart-shaped tongue tip when crying.