Causes of Mouth Breathing (Children and Adults)

Mouth breathing is not often considered as a medical problem but it does contribute to a number of complications and the underlying cause can affect a person’s quality of life in certain instances. Most of us breathe through our mouth at some point or the other, be it after strenuous physical activity or with the common cold, but in these cases it is short term and we usually return to “nose” (nasal) breathing thereafter. Some people do mouth breathe without realizing it and it is a matter of habit in these instances, rather than due to an underlying problem.

What is mouth breathing?

Mouth breathing describes the inhalation and exhalation of air through the mouth rather than through the nose. This is also known as open mouth breathing. While it can be a habit for some people, mouth breathing usually indicates an underlying problem such as nasal congestion or respiratory problems where oxygen exchange is insufficient. It may also be seen in cardiac conditions and other systemic diseases.

Why is mouth breathing bad?

It is inaccurate to refer to mouth breathing as bad but it can lead to certain complications in the long term. The function of both the nose and mouth differs. First it is important to understand the function of the nasal passages and how air is altered here in order to understand how these alterations do not occur in the mouth to the same degree as it would in the nose.

Air enters the nasal cavity through the nostrils. Here hairs and mucus secreted in the nose trap dust and microbes from the air that flows in. The turbinate air further slows down the movement of air as well as heats and moisturizes it. Smell receptors (olfactory receptors) in the nasal passages allows a person to detect chemical stimuli in the air and also contributes to taste.

Since the mouth lacks these hairs, dust and microbes may not be trapped before entering deeper into the airways. The saliva of the mouth does have some mucus but not to the same extent as the nose. Therefore people who mouth breathe are also prone to dryness of the mouth. Although smell may not always be considered to be vital, the lack of it can affect appetite, mood and sometimes even occupational activities in people who mouth breathe.

Causes of Mouth Breathing

Many of the causes of mouth breathing may be similar to the causes of difficulty breathing (dyspnea).


Rhinitis simply means inflammation of the nose. It refers to the mucosal lining the inside of the nasal cavity. Rhinitis is a very common condition and mainly occurs for two reasons – infections or allergies. Infectious rhinitis is usually seen with the common cold and other related upper respiratory tract infections. Allergic rhinitis, commonly referred to as hay fever, is more long term and seen in people with a history of allergies.


The paranasal sinuses are continuous with the nasal cavity. Sinusitis is a common condition that may also be related to infections or allergies. Inflammation of the paranasal sinuses is usually associated with nasal inflammation (rhinitis) and collectively it is known as rhinosinusitis. A deviated septum, trauma to the nose and nasal polyps are some of the other causes of sinusitis.


Another common cause of nasal congestion and mouth breathing in children is adenoiditis. The adenoids are a small mass of lymphoid tissue (similar to the tonsils) located at the back of the nasal cavity. When this tissue becomes inflamed, it is known as adenoiditis. The swelling is usually due to an infection. Adenoiditis is mainly seen in young children but can sometimes occur in adults. It is often associated with tonsillitis.

Airway Disease

A number of different lower airway diseases may also lead to mouth breathing although the nasal passages are clear. Mouth breathing in these cases is due to the need to take in more air. The two more common lower airway diseases where mouth breathing may be seen includes:

  • Asthma is where the tiny muscles in the bronchi goes into spasm thereby constricting the airways. Swelling of the airways and mucus build up further narrows it. This is usually episodic.
  • Bronchitis is the inflammation of the bronchi often caused by infections. It can be acute or chronic. The latter is associated with long term cigarette smoking as part of chronic obstructive pulmonary disease (COPD).
  • Obstructive sleep apnea where the tissue of the throat collapses and thereby blocks the airway. Obesity is a major risk factor.

Lung Diseases

The disturbance of gas exchange due to diseased lung tissue may also lead to mouth breathing as a person attempts to take in more air through the mouth. It may be infectious or non-infections in nature.

  • Pneumonia is inflammation of lung tissue due to an infection. Viruses and bacteria are the more common causes.
  • Emphysema is the destruction of lung tissue with a loss of elasticity usually as a result of long term smoking. It is a chronic obstructive pulmonary disease (COPD) like chronic bronchitis.
  • Pneumoconiosis is a lung disease associated with long term inhalation of dust and chemicals that damage lung tissue. Initially there is inflammation but in time there may be scarring of the lung tissue.
  • Pneumonitis is also inflammation of the lung tissue but usually refers to non-infectious causes as a result of allergies or irritation from substances inhaled in the air, such as molds or bird excrement.

Other Causes

There are a host of other conditions that may cause mouth breathing either due to the low oxygen levels in the blood, high carbon dioxide levels, inadequate oxygen distribution or other such mechanisms including psychological factors. This may include:

  • Heart failure as the blood is not adequately circulated. One of the common reasons is a heart attack (myocardial infarction), weakening or stiffening of the heart tissue or heart infections.
  • Anemia where the oxygen-carrying component of blood, hemoglobin, is deficient as is see with iron-deficiency anemia or hemolytic anemia.
  • Shock arising from blood loss or severe dehydration which affects the blood volume significantly. It may also arise from severe trauma, anaphylatic reactions, poisoning, “blood poisoning” (infection) and severe burns.
  • Kidney failure where the build up of wastes in the blood and inability to neutralize circulating carbon dioxide may lead to shortness of breath and mouth breathing as a result.
  • Anxiety and panic attacks may lead to mouth breathing as a result of the nervousness and can also result in hyperventilation.
  • Central sleep apnea where breathing stops due to signals from the brain (central) not being relayed correcly and the breathing muscles then cease.

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