Every child breathes through the mouth when they have a cold or are running around at sport, and that is nothing to worry about. The pattern worth a closer look is the child whose lips sit apart most of the day, who snores on most nights and who seems to have a blocked nose all year. Habitual mouth breathing like this is often a sign of a blocked airway, and because a child's jaws are still growing, it has been linked with changes in how the bite and face develop.
Signs parents tend to notice first
- lips apart while watching TV, reading or concentrating
- snoring, noisy breathing or very restless sleep
- waking with dry, cracked lips or asking for water through the night
- a nose that always seems blocked, or a nasal voice
- breath that stays unpleasant despite brushing
- tiredness, irritability or difficulty concentrating at school
- dark circles under the eyes
None of these alone proves there is a problem, but several together are worth raising with your dentist or GP.
A blocked airway is the usual cause
In young children, the most common reason is enlarged adenoids or tonsils. These lymph tissues are at their largest in the preschool and early school years and can crowd the back of the nose and throat. Allergic rhinitis, hay fever and frequent colds are the next most common causes, and less often a deviated septum is involved. Sometimes the habit carries on after the original blockage has settled, simply because the child has become used to it.
Thumb or finger sucking can sit alongside mouth breathing and add its own effects on the front teeth. A dentist will usually ask about both.
How it may affect the growing bite
With the lips closed and breathing through the nose, the tongue normally rests up against the palate and helps support the width of the upper jaw from the inside. When the mouth hangs open, the tongue tends to drop to the floor of the mouth while the cheek muscles keep pressing inward. Over years, studies have associated this with:
- a narrower, higher arched upper jaw
- a posterior crossbite, where upper back teeth close inside the lower ones
- upper front teeth that sit further forward (an increased overjet)
- less room in a narrow jaw for the adult teeth, which may add to crowding
- a longer lower face with the lips apart at rest
The research shows an association rather than proving mouth breathing alone causes these changes, and genetics plays a large part in jaw shape. Even so, the pattern is consistent enough that dentists look for it. Our guide to overbite, underbite and crossbite explains these bite problems in more detail.
Sleep matters as much as teeth
Snoring in children is not always harmless. Some children who mouth breathe have sleep disordered breathing, including obstructive sleep apnoea, which can affect behaviour, attention, mood and growth. Bedwetting after it had stopped and frequent waking can also be clues. If your child snores most nights, see your GP, who may refer to a paediatrician or ENT surgeon. Our article on snoring and sleep apnoea has more background.
Who to see, and in what order
A dentist or OHT can examine the teeth and jaws, look at the tonsils, ask about sleep and habits, and point out early bite changes. Your GP looks after the nose and airway and decides whether an ENT opinion is needed; when enlarged adenoids or tonsils are the cause, removing them can restore nasal breathing for many children.
If the upper jaw is already narrow, a dentist or registered orthodontist may suggest monitoring or early treatment. In growing children, a conventional palatal expander can widen the upper jaw, and timing matters because expansion is more straightforward while the midpalatal suture is still immature. An early orthodontic check, often around age seven, helps catch these issues at a useful point.
At home
Work with your GP to keep allergies and congestion under control, since a clear nose makes nasal breathing easier. A dry, open mouth also raises the risk of decay and gum inflammation, so brushing twice a day with a fluoride toothpaste suited to your child's age matters; our guide to cleaning young children's teeth covers the basics. If the habit continues once the airway is clear, your dental team can suggest gentle ways to encourage lip closure.
Common questions from parents
Will my child grow out of it?
Sometimes. Adenoids usually shrink later in childhood, and the mouth breathing may ease. Any bite changes that developed in the meantime may not reverse, which is why earlier assessment is worthwhile.
Is my child too young for a dental check?
No. Children can see a dentist from their first teeth, and eligible children can have care bulk billed under the Child Dental Benefits Schedule.
Does mouth breathing always mean an expander is needed?
No. Many children only need the cause treated and their bite monitored. An expander is considered when the upper jaw is narrow or there is a crossbite.
If you have noticed your child breathing through their mouth, our dentists and oral health therapists can check their teeth and bite, talk through sleep and habits, and help coordinate care with your GP. See our current deals page for current options. This article is general information and not a substitute for personal dental or medical advice.
