CPAP, or continuous positive airway pressure, is primarily used to treat obstructive sleep apnea, a condition where your airway repeatedly collapses during sleep, cutting off breathing for seconds at a time. The machine delivers a steady stream of pressurized air through a mask to keep your airway open throughout the night. Beyond sleep apnea, CPAP is also used in hospitals for acute heart failure and in neonatal units for premature infants with breathing difficulties.
How CPAP Works
A CPAP machine pulls in room air, filters it, and pressurizes it before pushing it through a tube into your mask. That pressurized air acts like a splint inside your throat, preventing the soft tissues from collapsing inward and blocking your airway. Most machines operate within a pressure range of 4 to 20 cm H₂O, and your sleep specialist sets the exact level based on your needs. Some machines include a built-in humidifier that adds moisture to the air, which helps reduce dryness and irritation in your nose and throat.
Obstructive Sleep Apnea: The Primary Use
The vast majority of people using CPAP have obstructive sleep apnea. During sleep, the muscles in the back of your throat relax so much that the airway narrows or closes completely. Each time this happens, your brain briefly wakes you to reopen the airway. These interruptions can happen dozens or even hundreds of times a night without you fully realizing it, leaving you exhausted, foggy, and at higher risk for serious health problems.
Sleep apnea is diagnosed using a measurement called the apnea-hypopnea index (AHI), which counts how many times per hour your breathing stops or becomes dangerously shallow. An AHI of 15 or more events per hour confirms the diagnosis. An AHI as low as 5 events per hour also qualifies if you have symptoms like excessive daytime sleepiness, loud snoring, waking up gasping or choking, morning headaches, or cardiovascular conditions such as high blood pressure, heart disease, or a history of stroke.
Predictive features that often point toward sleep apnea include observed gasping during sleep, a neck circumference greater than 16 inches, and episodes of falling asleep during the day when you shouldn’t be.
Benefits Beyond Breathing
CPAP does more than stop snoring. Consistent use produces measurable improvements in blood pressure, brain function, and daily energy levels.
For people with resistant high blood pressure, CPAP lowers 24-hour diastolic blood pressure by an average of 3.2 mmHg, according to the HIPARCO clinical trial published in JAMA. That number might sound small, but at a population level, even a few points of blood pressure reduction meaningfully lowers the risk of heart attack and stroke.
Cognitive function also improves substantially. A study published in the journal SLEEP found that after six months of CPAP use, participants showed significant gains in working memory, sustained attention, reaction time, and the ability to filter out mental distractions. Daytime sleepiness scores dropped by more than a third, falling from an average of about 12 on the Epworth Sleepiness Scale (where anything above 10 signals excessive sleepiness) to roughly 8, which is in the normal range. Many users describe this as a dramatic shift in how clearly they can think and how alert they feel during the day.
Hospital and Neonatal Uses
Outside the home, CPAP plays a role in emergency and intensive care medicine. In patients experiencing acute heart failure with fluid buildup in the lungs, CPAP can improve breathing, oxygen levels, and comfort without requiring a breathing tube. Studies show it reduces the rate of intubation compared to standard oxygen therapy, shortens ICU stays, and preserves the patient’s ability to speak, eat, and cough naturally.
CPAP has been used in neonatal care since 1971 for premature infants born with underdeveloped lungs. A specialized version called bubble CPAP helps keep the tiny airways open, reducing the need for mechanical ventilation and, in some cases, lowering the amount of supplemental lung medication these infants require.
Choosing the Right Mask
CPAP masks come in several styles, and the right one depends on how you breathe at night and what feels comfortable on your face.
- Nasal pillow masks are the smallest option. Two soft inserts sit just at the nostrils. They work well if you feel claustrophobic with larger masks, want to read or watch TV in bed, or have facial hair that interferes with a seal.
- Nasal masks cover the nose and are a good choice if your doctor has prescribed a higher pressure setting or if you tend to move around a lot while sleeping.
- Full-face masks cover both the nose and mouth. These are typically recommended if you breathe through your mouth at night or have nasal congestion that makes nose-only breathing difficult.
- Hybrid (oral) masks deliver air through the mouth and may suit people who wear glasses or who consistently mouth-breathe.
If you start with a nasal mask but find yourself mouth-breathing, your provider will usually suggest trying a heated humidifier or chin strap before switching to a full-face option.
Common Side Effects
Most CPAP side effects are annoying rather than dangerous, and nearly all of them can be managed with adjustments. Nasal dryness and congestion are the most frequent complaints, often solved by adding or adjusting a humidifier. Skin irritation or pressure marks on the face typically mean the mask doesn’t fit properly or the straps are too tight.
Some people experience aerophagia, which is the medical term for swallowing air. This can cause bloating, excessive burping, and gas pain. It tends to happen when the pressure is set too high or when you’re breathing through your mouth with a nasal mask. Your provider can adjust the pressure or switch your mask type to reduce it.
What Counts as Regular Use
CPAP only works when you actually wear it. Medicare and most insurance companies define adequate use as wearing the device for at least 4 hours per night on 70% of nights during any consecutive 30-day stretch within the first 3 months. If you don’t hit that threshold, your insurer may stop covering the equipment.
That 4-hour minimum is a coverage requirement, not a health recommendation. The more hours you wear CPAP each night, the greater the benefits for blood pressure, cognitive function, and daytime alertness. Most sleep specialists encourage working toward wearing it for your entire sleep period, even if it takes weeks or months to build up to that comfortably.