You check on your sleeping baby and there it is: that tiny mouth hanging open. It looks adorable in a photo and slightly alarming at 2 a.m., when every parenting instinct asks the same question: is this normal? Should babies breathe through their nose?
Here is the short answer: babies are designed to breathe through their nose, and an occasional open mouth during deep sleep, especially during a cold, is usually nothing to worry about. But mouth breathing that is persistent, every night, cold or no cold, is worth a conversation with your pediatrician, because it usually means something is making nose breathing harder than it should be.
This guide covers why babies sleep with their mouth open, which causes are temporary and which deserve attention, the signs that separate “cute quirk” from “book an appointment,” and what you can safely do at home tonight.
Table of Contents
Is It Normal for a Baby to Sleep With Their Mouth Open?
Newborns and young infants are preferential nose breathers: their anatomy is built to breathe through the nose while feeding, and nose breathing filters, warms, and humidifies air on the way in. Healthy babies breathing comfortably will usually sleep with lips closed.
So an open mouth during sleep is common, but it is not the design default. Occasional mouth-open sleep happens during deep sleep phases, after crying, or when a stuffy nose forces a temporary workaround. The pattern to watch is chronic mouth breathing: every night, most of the night, even when your baby is healthy 1.
Why Do Babies Sleep With Their Mouth Open?
Congestion. The most common reason by far. Colds, dry air, and irritants block tiny nasal passages, and babies switch to mouth breathing until the nose clears.
Allergies. Ongoing nasal inflammation from environmental allergies can keep passages swollen, making mouth breathing a nightly habit.
Enlarged adenoids or tonsils. Adenoid tissue sits exactly where it can block nasal airflow. Persistently enlarged adenoids are one of the most common medical causes of chronic mouth breathing in babies and toddlers 1.
Deep sleep relaxation. Jaw muscles relax during deep sleep, and some babies’ mouths simply fall open without any airflow problem at all.
Habit after illness. Some babies keep mouth breathing for a while after the congestion that started it has resolved.
When Mouth Breathing Matters
Chronic mouth breathing is not just a cosmetic quirk. Over time it is associated with poorer sleep quality, and in children it can affect dental and facial development 1. More immediately, persistent mouth breathing at night can be a sign of sleep-disordered breathing, a spectrum that runs from habitual snoring to obstructive sleep apnea 2.
Talk to your pediatrician if mouth breathing comes with any of these:
Loud, regular snoring (most nights, not just with colds)
Pauses in breathing, gasping, or snorting awake
Restless, sweaty sleep with unusual positions (head tilted far back to open the airway)
Daytime crankiness, poor feeding, or excessive sleepiness despite enough hours in bed
Mouth breathing during the day as well as at night
None of these signs means something is definitely wrong. They simply move the question from the internet to a professional who can look at your actual baby, which is always the better place for it.
Worth knowing
Fragmented nights have many causes, and breathing is only one of them. In Betteroo’s State of Baby Sleep survey of tens of thousands of families, night waking peaks at 7 to 9 months with 67% of babies waking 3+ times, breathing issues or not. If your baby breathes comfortably but wakes constantly, the schedule is usually the lever, not the airway.
What You Can Do at Home
Clear the nose before sleep. Saline drops plus a nasal aspirator before bedtime and naps is the single most effective home measure during congestion.
Run a cool-mist humidifier. Dry air thickens mucus and irritates small airways. Aim for roughly 40 to 50% humidity; our baby humidifier guide covers what actually matters.
Reduce airborne irritants. Smoke, strong fragrance, and dust all inflame infant nasal passages.
Keep sleep safe and simple. Back to sleep on a firm, flat, bare surface, per AAP guidance 3. No positioners or wedges, which are unsafe and do not fix breathing.
Do not tape, prop, or close your baby’s mouth. Mouth-taping products are dangerous for infants. If nose breathing is hard, the answer is finding out why, never forcing the mouth shut.
Mouth Open vs. Other Sleep Quirks
Babies are noisy, twitchy, surprising sleepers, and most of it is normal. Grunting and squirming have their own explanations (see our guide to baby grunting in sleep), and crying out without waking is covered in why babies cry in their sleep. The skill of reading what is normal, what is a phase, and what needs attention is most of the job, and you build it faster than you think.
Baby Sleeping With Mouth Open FAQ
Is it OK for my newborn to sleep with their mouth open?
Occasionally, yes, especially during deep sleep or a stuffy nose. Newborns are preferential nose breathers, so if your newborn breathes through an open mouth most of the time, mention it at your next pediatrician visit, and sooner if feeding or breathing seems labored.
Does mouth breathing mean my baby has sleep apnea?
Usually not. Most mouth-open sleep is congestion or deep-sleep relaxation. Sleep apnea becomes more likely when mouth breathing is paired with loud regular snoring, gasping, breathing pauses, or restless sweaty sleep. Those signs warrant a pediatrician evaluation.
Can teething cause mouth breathing?
Indirectly. Teething increases drool and can come with mild congestion, which nudges babies toward mouth breathing for a few days. It should resolve as the tooth comes through.
Will my baby grow out of mouth breathing?
If the cause is temporary (a cold, dry air, a teething week), yes. If the cause is structural or ongoing, such as enlarged adenoids or persistent allergies, it tends not to resolve on its own, which is why chronic mouth breathing deserves a medical look.
Should I use saline drops every night?
Saline is safe to use regularly during congested stretches, ideally before sleep and feeds. If you find your baby needs nightly saline for weeks on end just to breathe through their nose, that persistence itself is the signal to check in with your pediatrician.
Wondering what else is normal at your baby’s age?
Get a personalized sleep plan built around your baby’s age, temperament, and your family’s needs.
An open mouth during sleep is usually a stuffy nose, a deep sleep phase, or a passing habit, not an emergency. The question that matters is persistence: a baby who mouth-breathes every night, healthy or not, deserves a pediatric look at why the nose is not doing its job. Trust the pattern, not the single night, and trust your instinct to ask.
Marcus, C.L., et al. (2012). Diagnosis and Management of Childhood Obstructive Sleep Apnea Syndrome. Pediatrics, 130(3), 576–584. https://pubmed.ncbi.nlm.nih.gov/22926173/
American Academy of Pediatrics. (2022). Sleep-Related Infant Deaths: Updated 2022 Recommendations for Reducing Infant Deaths in the Sleep Environment. https://pubmed.ncbi.nlm.nih.gov/35726558/
