The body's natural humidification process

The human body has its own humidification process that protects the respiratory system. Every time you take a breath, your nose, pharynx, and trachea humidify – add moisture to – the air so that it enters your lungs with the necessary humidity.

Your nose is responsible for about two-thirds of this process. As the air passes further into your airway, it becomes warmer and more humid. By the time air reaches your lungs it is at the ideal temperature and humidity. When you exhale your nose conserves water by recovering about a third of the moisture present in each exhaled breath. That moisture is then used to assist in the humidification of your next breath.

Environmental factors

Environmental factors can increase demands on your body's humidification process. If you travel to an extremely dry climate, you may experience a sore throat, nasal congestion, or irritated sinuses. You may also experience these symptoms in extremely cold climates-cold air tends to be less humid. In both cases, the lower humidity puts an extra burden on your body's normal equilibrium. Some people adjust quickly enough that the change in humidity doesn't affect them; some people may experience only temporary discomfort; however, some people may feel as if they can't adjust to the new climate.

Positive airway pressure and your body's natural humidification process

Just as some people have difficulty adapting to less humid climates, some people have difficulty adapting to positive airway pressure. In essence, positive airway pressure creates a new climate for your nose and upper airway because airflow is greater than what your body is accustomed to humidifying – and the greater your treatment pressure the more difficult this task becomes. Your nose may become tender or dry, or it may respond to the new environment by creating more mucus to protect its sensitive tissues. A humidifier can prevent and even reverse these symptoms by treating the air before it even reaches your nose.

Mouth breathing

If you breathe through your mouth, you may develop a dry throat. By breathing through your mouth, you bypass your nose, which is responsible for two-thirds of humidification. This means that you've tripled the humidification workload of your upper airway. If you add positive airway pressure on top of that you may start to experience stronger symptoms. Even if you're only exhaling through your mouth, you are still losing valuable moisture because you aren't allowing your nose to recover the moisture your body invested in the air as you "inhaled" it.

A vicious cycle

A 1997 study found that nasal symptoms cause mouth breathing and that mouth breathing causes nasal symptoms. Because one symptom causes another, a vicious cycle can develop. For example, some congestion leads to mild mouth breathing that can worsen the congestion that causes more severe mouth breathing.

Selecting a Humidification System

Humidification can resolve and prevent all of the symptoms mentioned above, but not all systems supply the same amount of humidification. There are two types of humidification device:

A heated humidifier can create a lot of water vapor, soothing extreme nasal dryness and irritation. Studies show that heated humidification is more effective than the alternative, passive humidification and can make therapy more comfortable

ResMed's HumidAire™ heated humidifiers

Passive humidification is beneficial for minor nasal symptoms or mouth leak. These devices are also handy for travel because they weigh less than heated humidifiers.

ResMed's Passover humidifiers

Related Issues
Medical reimbursement
In the US, humidification is not always covered by medical insurance. When it is, you may not have a choice between passive and heated humidification. In either case, speak with your clinician or insurance company to learn about your options.