Daniel More, MD, is a board-certified allergist and clinical immunologist with a background in internal medicine.

Although a continuous positive airway pressure (CPAP) machine can help you sleep better if you have sleep apnea, there are times when the device can cause you problems.

One of them is the build-up of moisture that can occur when a heated humidifier is used. This can cause the CPAP unit to make spitting sounds or the mask to fill with water. Both of these things can wake you up.

This article explains why this all-too-common problem occurs and how you can avoid it if you are struggling with your CPAP machine.

The build-up of moisture in a CPAP machine is most often due to the use of a heated humidifier. This is a concern since many experts advise CPAP users to use humidifiers to improve breathing.

There are several reasons to use a humidifier:

CPAP users over the age of 60 or those who have had surgery to treat sleep apnea are at greater risk of these symptoms.

A heated humidifier improves comfort in CPAP users by reducing dryness in the nose and mouth. There is a trade-off, however, when extra moisture is added to the air.

For CPAP to work at its best, you need heat and humidity in the mask and tubes to match the heat and humidity outside of the mask and tubes.

When humidity enters an unheated tube, the difference in temperature can cause moisture to condense. When this happens, small beads of water can collect and drip onto your face, causing what is known as "rainout."

The risk of rainout is increased if you sleep in a cold room. When the icy air meets with warm air, condensation is inevitable. If the humidity setting is high, the risk of rainout is also increased.

Another problem is that a cold room lowers the air temperature within the mask. Because the air is pressurized, the air being forced into the airways is colder. This is many people using CPAP have stuffy or runny noses.

Condensation occurs when the temperature outside of the CPAP mask and tubes is lower than the temperature and humidity within. This can cause "rainout" in which the condensed moisture drips on your face.

Rainout, as well as the gurgling and spitting of CPAP machines, is common among CPAP users. There are a few simple ways to avoid these problems and make CPAP more effective.

Using a heated tube, also known as a climate line, is the best way to avoid condensation problems. A climate line delivers the warm, moist air from the heated humidifier to the CPAP mask. This balances the internal and external temperature so that moisture does not condense.

Most newer CPAP units offer a climate line as a standard feature. Some models have heated wires that run the length of the tube to keep the temperature between 78 and 82 degrees F.

Older CPAP machines can be fitted with a special heated tubing attachment, allowing you to keep your current machine. Hybernite Rainout Control System is among the best-known brands.

A simpler option is to turn down the temperature of the humidifier or turn up the thermostat in your bedroom. It sometimes takes trial and error to get the balance just right, but doing so can help you avoid buying a new machine.

Start by finding the temperature you can sleep in comfortably. You can then lower the temperature on your humidifier little by little until you get the right balance.

Another useful tip is to put the CPAP machine on the floor. By doing so, the moisture that collects in the tubing does not run back to your face. (This doesn't always prevent spitting or sputtering sounds, however.)

You can also put the CPAP tubing under the bed covers. This will help warm the tube so that moisture is less likely to condense. There are also special fabric covers you can buy online that slip over the tubes to help keep them warm. SnuggleHose is one of the more well-known brands. You can make fabric covers as well.

There are a few simple ways to prevent CPAP condensation:

One of the common problems faced by CPAP users is the build-up of moisture in the mask and tubing. This can lead to rainout or gurgling sounds from the machine. Both of these problems are caused by the mismatch of temperature and humidity inside and outside of the CPAP machine.

A heated humidifier is a common cause of condensation, but a cold room can also contribute as icy air can cause the moisture in the tube to condense.

There are several ways to deal with this. This includes buying a machine with heated tubes, adjusting the temperature of the humidifier and/or bedroom, keeping the CPAP tubing under the bed covers, or placing the CPAP unit on the floor.

Don't let problems like rainout keep you from using your CPAP machine. In the end, you are on CPAP because sleep apnea is affecting your ability to sleep and raising the risk of other health concerns.

If you continue to have problems with your machine, speak with your sleep doctor or the device manufacturer, who can offer tips on how to resolve your concerns.

Generally, the best humidity level to avoid rainout on a CPAP machine is 3.

To remove water from CPAP tubing, run the CPAP without water in the reservoir to help push out excess water, or hang the tubing until it air dries.

Tossing and turning night over night can have a big impact on your quality of life. Our free guide can help you get the rest you need. Sign up for our newsletter and get it free.

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American Sleep Apnea Association. The importance of CPAP humidification.

Chou MSH, Ting NCH, El-Turk N, Harrington Z, Dobler CC. Treatment burden experienced by patients with obstructive sleep apnoea using continuous positive airway pressure therapy. PLoS One. 2021;16(6):e0252915. doi:10.1371/journal.pone.0252915

Nilius G, Domanski U, Schroeder M, Woehrle H, Graml A, Franke KJ. Mask humidity during CPAP: influence of ambient temperature, heated humidification and heated tubing. Nat Sci Sleep. 2018;10:135-42. doi:10.2147/NSS.S158856

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