Mouth breathing: why it happens, and what it does to the teeth and gums

The nose warms, moistens and filters the air; the mouth cannot do this. Cleveland Clinic defines mouth breathing as frequently taking in air through the mouth instead of the nose, and states that most people do this because they cannot get enough air through the nose. During a short cold, everyone breathes through their mouth; the problem is when this turns into a habit that carries on both by day and by night. Cleveland Clinic writes that for adults this is usually not a serious health problem, but that in children it can affect development.

The causes mostly lie in the nose. Cleveland Clinic lists a bent nasal septum (deviated septum), enlargement of the folds inside the nose (turbinates), enlarged adenoids or tonsils, nasal congestion, nasal polyps and sleep apnoea. Allergic rhinitis is also a common cause. The NHS writes that adenoids usually start to shrink at around the age of 4 and disappear by early adulthood; so in children the commonest cause is the adenoids, while in adults it is the structure of the nose and allergy.

The symptoms are most often noticed not from the mouth breathing itself but from its consequences. In adults, Cleveland Clinic lists bad breath, drooling during sleep, a dry mouth, tiredness, a hoarse voice and snoring. The NHS also points to breathing through the mouth at night among the main causes of a dry mouth, and writes that this happens when the nose is blocked or you sleep with your mouth open. If you wake up in the morning with a dry mouth and a parched throat, this is the commonest sign that your mouth stays open at night.

Mouth breathing has a measurable effect inside the mouth. In a study in New Zealand with 10 healthy volunteers, a sensor placed on the palate side of the upper front teeth showed that the pH in the mouth averaged 7.0 in normal sleep and 6.6 in sleep where they were forced to breathe through the mouth with a nose clip, and that the drop lasted longer. Saliva neutralises acids, repairs enamel and clears away bacteria; when the mouth dries out, this protection weakens. The researchers state that this may play a part in decay and acid wear; the study is small and did not directly measure the outcome for the teeth.

The effect on the gums has been studied most in children and adolescents. In a 2025 systematic review that examined 11 cross-sectional studies, bleeding gums, plaque build-up and gum changes were found more often in children and adolescents who breathe through the mouth; a link with decay, on the other hand, was seen only in early and advanced lesions, and the evidence is limited. These studies are observational; they do not show conclusively that mouth breathing causes these, but they point in the same direction. In a small clinical study in adults with 40 people who breathed through the mouth and had gum disease, more improvement in gum inflammation and bleeding was seen when a saliva substitute applied to the front teeth was added to gum treatment.

A picture often seen in the clinic: in people who breathe through the mouth, inflammation is often concentrated in the gums of the front teeth, in the area the lips do not cover. If the front gums are red and swollen even though brushing is good, one of the first questions the dentist asks is whether the mouth stays open at night. That is why, if only gum treatment is done and the airway is not addressed, the inflammation can come back. The evidence for this observation from large studies is limited; but this is the reasoning for asking about the nose and sleep alongside gum treatment.

In children, mouth breathing carries particular importance. Cleveland Clinic writes that in children who breathe through the mouth, changes in facial shape such as a narrow face, a receding jaw and crowded teeth, growth problems and behaviour problems can be seen. It links the behaviour problems to sleep: according to some specialists, these children have sleep apnoea or other sleep problems, and lack of sleep can cause restlessness and behaviour resembling attention deficit. A 2026 systematic review that examined 13 studies also reports that most of the studies found a significant link between mouth breathing and the severity of sleep apnoea in children, but that the results can be inconsistent because the diagnostic methods differ. A review examining the link between allergic rhinitis and crowded teeth, while recommending early diagnosis and treatment of nasal blockage, stresses that the current data are not enough to establish cause and effect.

For people with dentures and implants, the subject matters through dry mouth. In a systematic review that examined nine studies, six studies showed that a dry mouth had a negative effect on speaking, chewing and the retention of removable dentures. With a dry mouth, the NHS recommends not sleeping in dentures. There are few studies directly examining the effect of mouth breathing on teeth fixed on implants; but in a dry mouth, plaque builds up more easily, and the health of the gum around implants depends on plaque control. If implants or full-mouth treatment are being planned, telling the team about snoring, sleeping with your mouth open and a blocked nose allows the care plan to be drawn up accordingly.

The first list describes the picture that suggests a temporary or simple cause; the second list describes the picture that calls for seeing a doctor.

The sequence below moves from the checks you can do at home to the doctor's assessment.

1. 1

   The lip-closure test

   Close your mouth and breathe calmly through your nose alone for a minute. If you struggle and soon feel the need to open your mouth, the nasal passage is not open enough. Cleveland Clinic writes that at the examination doctors check whether you can breathe with your mouth closed.

2. 2

   The mirror and water tests

   Cleveland Clinic describes two simple examination tests: misting on a mirror held under the nose shows that you are breathing through the nose; holding water in the mouth forces you to breathe through the nose. Close one nostril and try with the other; note the difference between the sides.

3. 3

   Night-time observation

   Ask the person who sleeps next to you whether your mouth is open, whether you snore and whether your breathing stops. The NHS writes that sleep apnoea can be hard to notice and that someone watching you while you sleep can help. With children, a few minutes of video taken while they sleep tells the doctor a great deal.

4. 4

   GP or paediatrician

   Allergy, nasal blockage and sleep symptoms are assessed. If there is snoring and pauses in breathing, a referral for a sleep test can be made; the doctor referring you decides whether the test is done at home or in a sleep laboratory.

5. 5

   Ear, nose and throat examination

   The nasal septum, the folds inside the nose, polyps, the adenoids and the tonsils are examined. If needed, the back of the nose is looked at with an endoscope. Treatment is planned according to this examination.

6. 6

   A dentist and, if needed, an orthodontist

   The dentist assesses gum inflammation, plaque, decay and the signs of a dry mouth. In children, an orthodontic assessment of the jaw and tooth alignment is requested; findings such as a narrow upper jaw are dealt with together with an ear, nose and throat specialist.

Cleveland Clinic writes that treatment means treating the condition that makes breathing through the nose difficult. The options vary with the cause.

The following are the wrong decisions commonly seen in this area, and what they cost.

How long it takes to improve depends on the cause. The sequence below is a general framework; the plan of the doctor following you takes priority.

1. When the nose clears

   When the allergy or infection is treated, the mouth often closes by itself; morning dryness and bad breath decrease.

2. After surgery

   The NHS writes that after adenoid surgery recovery usually takes about a week, and that during this time there can be a blocked nose and bad breath.

3. If the habit continues

   If the mouth stays slightly open even though the nose has cleared, lip-closure and tongue-posture exercises (therapy for the muscles of the mouth and face) can come up. The NHS lists mouth and face muscle exercises among the treatments used for sleep apnoea.

4. For the gums

   Once the airway has improved, the result of gum treatment is more lasting. The dentist sets the interval between check-ups according to how the inflammation progresses.

We do not give a single figure, because the cause of mouth breathing ranges from a simple allergy to a structural problem that needs surgery. The items that determine it:

Investigating the cause

Whether an ear, nose and throat examination, an endoscopy, allergy tests or a sleep test are needed.

Type of treatment

Medication, surgery, CPAP or an oral appliance differ in scope.

The effects inside the mouth

The need for gum treatment, treatment for decay or, in children, orthodontic treatment.