Why Do I Hum When I Sleep? Causes and What to Do

Humming, moaning, or groaning during sleep is almost always a condition called catathrenia, sometimes known as nocturnal groaning. It affects roughly 4% of adults, though it often goes undiagnosed because the sleeper rarely knows it is happening and bed partners may simply assume it is an unusual form of snoring.¹ The sound is produced during a long, slow exhalation, not while breathing in, and it has a distinctly musical or tonal quality that sets it apart from ordinary snoring. Catathrenia is considered medically harmless, but it can be loud enough to disrupt a partner’s sleep and alarming enough to send people searching for answers.

What Catathrenia Actually Sounds Like

The typical episode follows a predictable sequence. You take a deep breath in, then exhale very slowly over several seconds while producing a sustained, pitched sound. The exhalation is unusually long, and the humming or groaning happens throughout most of it. The episode ends with a brief, faster puff of air, followed by another deep inhalation, and the cycle starts again.² A single event lasts anywhere from about 5 seconds to over 20 seconds, with an average around 13 seconds, and events tend to cluster in bouts throughout the night.³

The sound itself is strikingly different from snoring. Detailed acoustic studies have found that catathrenia sounds are tonal, with clear harmonics and a regular waveform, much like a voice or a musical note held at a steady pitch. The average fundamental frequency sits around 195 Hz, roughly in the range of a speaking voice. Snoring, by contrast, is irregular and noisy, with no discernible pitch or harmonic structure.⁴ Some people produce a smooth, sinusoidal tone, while others make a rougher sawtooth-shaped sound at a slightly different pitch, but both types remain rhythmic and stable in a way that snoring never is.⁵

Bed partners often describe the noise as eerie, monotone moaning, humming, or even a high-pitched whine. The sound is genuinely vocal, produced by vibration of the vocal folds in the larynx, which is why it sounds so different from the floppy-tissue rattle of snoring.⁶ The intensity averages around 66 decibels, comparable to normal conversation volume, though some episodes are louder.⁴

Why Your Body Does This

Researchers still do not have a single definitive explanation for catathrenia, but the leading theory points to an abnormality in the brain’s control of breathing during sleep. While you are awake, your breathing is regulated by both voluntary control and automatic systems. During sleep, the voluntary system shuts down and the automatic respiratory drive takes over completely. In people with catathrenia, that automatic drive appears to occasionally misfire, producing an unusually prolonged exhalation during which the vocal folds partially close and vibrate.⁷

One hypothesis is that this pattern represents a vestigial, or leftover, type of breathing from infancy. Newborns have a breathing pattern that includes long exhalations with partial vocal cord closure, which helps maintain air pressure in the lungs. In most people this pattern disappears as the nervous system matures, but in those with catathrenia it may persist in a muted form that only surfaces when conscious breathing control is absent during sleep.⁷ The fact that groaning alternates with perfectly normal breathing in the same night, and that people experience no lasting respiratory problems, supports the idea of an intermittent glitch in the respiratory control center rather than any structural problem with the airway.

Interestingly, a large portion of catathrenia episodes are connected to brief micro-arousals in the brain. One study found that about 84% of catathrenia periods were associated with a cortical arousal either just before or at the start of the episode, and these arousal-linked episodes lasted significantly longer than those without one.² This does not mean you wake up during them. These are tiny blips of brain activation you will never remember, but they suggest the episodes are triggered at the boundary between deeper and lighter sleep.

When During the Night It Happens

For years, catathrenia was thought to occur mainly during REM sleep, the stage associated with dreaming. More recent work paints a more complicated picture. A systematic review of existing cases found that episodes split almost evenly, with about half occurring in non-REM sleep and half in REM sleep.⁸ There was also a sex-based pattern: women tended to have more episodes during non-REM sleep, while men had more during REM.⁸

This has practical implications. Because REM sleep becomes more concentrated in the second half of the night, people whose catathrenia is REM-dominant tend to be noisiest in the early morning hours. If your bed partner reports the humming mainly in the predawn period, that pattern is consistent with REM-linked catathrenia. If the sounds start soon after you fall asleep and continue throughout the night, a mix of REM and non-REM episodes is more likely.

Who Gets Catathrenia

Catathrenia does not favor one sex over the other. Clinical case series show roughly equal numbers of men and women.⁹ Affected individuals tend to be on the leaner side, with an average body mass index around 20 to 21, and onset typically occurs in the late teens, around age 18 on average.⁹ This demographic profile is essentially the opposite of obstructive sleep apnea, which skews toward older, heavier individuals, and it is one more reason catathrenia should not be confused with apnea or snoring.

Children can develop catathrenia as well. In a pediatric case series, the average age of onset reported by parents was around six years old, though some parents traced the sounds back to infancy. Diagnosis lagged behind, coming at an average age of about eight.¹⁰ Parents of children with catathrenia are often the ones who first bring the problem to medical attention, worried by the unusual nighttime sounds. The reassuring news is that in children, as in adults, catathrenia does not appear to cause health problems beyond the noise itself.

Is It Really Harmless?

By all available evidence, yes. No studies have linked catathrenia to drops in blood oxygen levels, cardiovascular problems, or degraded sleep quality for the person doing the groaning. During episodes, heart rate dips slightly during the long exhalation and ticks back up afterward, but oxygen saturation stays stable.³ The person making the sounds rarely wakes from them and typically feels rested in the morning. The real burden falls on bed partners and family members who lose sleep because of the noise.

That said, the social and relational consequences are not trivial. Sleeping in separate rooms, anxiety about sharing hotel rooms or sleeping in new environments, and embarrassment are all commonly reported. Because catathrenia cases are rarely referred to sleep centers despite the condition’s real prevalence, many people live with it for years without knowing it has a name.¹

Conditions That Look Like Catathrenia

The most common misidentification is snoring. As discussed above, the sounds are acoustically different: catathrenia is tonal and pitched, snoring is chaotic and noise-like. But in the middle of the night, few bed partners are conducting frequency analysis. A useful rule of thumb is timing within the breath. Snoring happens on the inhale (or sometimes on both inhale and exhale), while catathrenia sounds happen exclusively during exhalation. If the sound only occurs as your partner breathes out, catathrenia is the more likely explanation.

A more serious mimic is nocturnal seizures. Frontal lobe seizures can cause vocalizations during sleep that resemble catathrenia, including moaning or humming. The treatments are completely different: catathrenia is managed with airway devices, while seizures require anticonvulsant medication. If nighttime vocalizations are accompanied by unusual body movements, sudden awakenings with confusion, or any neurological symptoms during the day, evaluation for seizures should be part of the workup.¹¹

Obstructive sleep apnea is also in the differential. Some researchers have questioned whether catathrenia is even a separate condition or merely an unusual variant of sleep-disordered breathing, since the prolonged exhalation against a partially closed airway has some mechanical similarities to apnea events.¹² The classification question remains unresolved in sleep medicine, but from a practical standpoint it matters less than getting the right treatment, and both conditions respond to positive airway pressure therapy.

Getting a Diagnosis

If you suspect catathrenia, the standard diagnostic tool is a polysomnography study, an overnight sleep test conducted at a sleep lab. The critical addition for catathrenia diagnosis is audio and preferably video recording during the study. Without audio capture, the characteristic groaning sounds can be missed entirely, since the breathing pattern alone on a sleep study tracing can look similar to other conditions. With audio-visual recording, clinicians can see the classic sequence of deep breath in, prolonged tonal exhalation, brief terminal exhalation, and arousal.³

If you are trying to explain the problem to a doctor before getting a formal study, a smartphone recording made by your bed partner is genuinely useful. The tonal, humming quality of catathrenia is distinctive enough that an experienced sleep specialist can often recognize it from a recording alone, even before polysomnography confirms it.

Treatment Options That Work

The most studied treatment for catathrenia is continuous positive airway pressure, or CPAP, the same device used for obstructive sleep apnea. It works by delivering a steady stream of pressurized air through a mask, which keeps the airway open and prevents the vocal folds from vibrating during exhalation. In one clinical series, CPAP reduced groaning events by an average of about 76%.¹³ A larger study of 26 patients treated with CPAP showed groaning frequency dropping from about 10.6 events per hour to 5.7 per hour, a meaningful reduction though not complete elimination.¹⁴

CPAP is effective, but it comes with the downsides familiar to anyone who has tried it for apnea: mask discomfort, nasal dryness, and the inconvenience of traveling with a machine. For people who find CPAP intolerable, a mandibular advancement device, a custom-fitted oral appliance that pushes the lower jaw slightly forward, is an alternative. A clinical trial of these devices in catathrenia patients found that the groaning index dropped significantly, from a median of 5.8 events per hour to 2.8.¹⁵ Oral appliances are smaller, quieter, and easier to travel with, which makes them a practical option for people whose catathrenia is moderate.

No medication has been shown to reliably treat catathrenia. Various drugs used for other sleep disorders, including benzodiazepines and antidepressants, have been tried in individual case reports with inconsistent results. For now, airway-based therapies remain the only treatments with supporting evidence.

Practical Steps if You Are Not Ready for Medical Devices

Not everyone with catathrenia needs or wants treatment with CPAP or an oral appliance, particularly if the groaning is mild and the main concern is a bed partner’s sleep. Some practical strategies that people commonly use include:

Positional changes: Some individuals report fewer episodes when sleeping on their side rather than their back. This is not well studied in formal trials for catathrenia specifically, but positional therapy is low-cost and harmless to try.
White noise machines: Because catathrenia is tonal and relatively steady, a white noise machine or fan can help mask the sound for a bed partner more effectively than it would for the erratic noise of snoring.
Earplugs for the bed partner: Simple foam earplugs or noise-canceling earbuds designed for sleep can make a meaningful difference. The burden of catathrenia often lands on the listener, and protecting their sleep is a valid part of managing the condition.
Alcohol and sleep deprivation awareness: Both alcohol and being overtired tend to increase the duration and depth of REM sleep and may worsen any REM-linked parasomnia. Keeping a consistent sleep schedule and moderating alcohol intake in the evening is reasonable general advice.

The Classification Debate

Sleep specialists have gone back and forth for over a decade on what catathrenia actually is. It was first classified as a parasomnia, lumped in with sleepwalking, sleep talking, and similar behaviors that occur during sleep without conscious control.¹² But the fact that it involves the airway and responds to CPAP has led some researchers to argue it belongs in the sleep-disordered breathing category alongside obstructive sleep apnea and central sleep apnea. Adding to the confusion, one study found that only about 5% of the groaning events in their patients technically met the strict diagnostic criteria laid out in international classification manuals, raising the question of whether the definition itself needs updating.¹³

For you as a patient, the classification debate is largely academic. Whether your doctor calls it a parasomnia or a breathing disorder, the symptom is the same, the workup is the same, and the treatment options are the same. What matters is that the condition is recognized and that you are offered evidence-based options if the groaning bothers you or your household. If your doctor is unfamiliar with the term catathrenia, pointing them toward the sleep medicine literature, or bringing that smartphone recording from your bed partner, can help move the conversation forward.

Catathrenia Across a Lifetime

One of the less-studied questions is what happens to catathrenia over time. Because it tends to begin in adolescence or early adulthood, many people live with it for decades. The pediatric literature suggests that some children may outgrow the condition or see it diminish in frequency, though longitudinal data is limited.¹⁰ In adults, catathrenia appears to be a chronic but stable condition. It does not progressively worsen in the way that untreated sleep apnea often does, and it does not evolve into a more serious respiratory or neurological disorder. The absence of long-term health consequences is one of the most consistent findings in the literature.⁷

For people who have dealt with unexplained nighttime humming for years, simply learning the name of the condition and understanding that it is not dangerous can be the most valuable outcome of the diagnostic process. The sounds will not hurt you. The question is whether they bother you or the people around you enough to pursue treatment, and if so, effective options exist.

1
PubMed. Lamentations in the night: A systematic review on catathrenia
2
PubMed Central. Catathrenia, a REM predominant disorder of arousal?
3
American Journal of Respiratory and Critical Care Medicine. A Case of Catathrenia Captured on Polysomnography with Audio–Visual Recording
4
Physiological Measurement. Polysomnographic characteristics and acoustic analysis of catathrenia (nocturnal groaning)
5
PubMed. Acoustic characteristic of catathrenia and snoring: different subtypes of catathrenia
6
PubMed Central. Sleep-Related Rhythmic Sound From the Vocal Cords: A Possible Atypical Form of NREM Parasomnia
7
PubMed. Catathrenia (nocturnal groaning): an abnormal respiratory pattern during sleep
8
PubMed Central. The clinical characteristic of catathrenia: a new look at an old issue-a systematic review of existing literature
9
PubMed Central. Characteristics of clinical descriptive variables and polysomnographic findings of catathrenia
10
PubMed Central. Catathrenia in children: clinical presentation, polysomnographic features, natural history, and response to therapy
11
American Epilepsy Society. Nocturnal Seizures Masquerading as Catathrenia: A Case Report
12
PubMed Central. Catathrenia: parasomnia or uncommon feature of sleep disordered breathing?
13
Sleep and Breathing. Nocturnal moaning and groaning – Catathrenia or nocturnal vocalizations
14
Sleep. The Clinical Characteristics And Therapeutic Efficacy Of Catathrenia
15
PubMed Central. Mandibular advancement device as treatment trial for catathrenia (nocturnal groaning)