# Snoring

Snoring is an abnormal breath sound caused by partially obstructed, turbulent airflow and vibration of tissues in the upper respiratory tract (e.g., uvula, soft palate, base of tongue) which occurs during sleep. It usually happens during inhalations (breathing in).
Primary snoring (also termed simple snoring, non-apneic snoring, or habitual snoring) is snoring without any associated sleep disorders and without any health effects. It is usually defined as apnea–hypopnea index score less than 5 per hour and lack of daytime sleepiness.
Snoring may also be a symptom of upper airway resistance syndrome or obstructive sleep apnea (apneic snoring). In obstructed sleep apnea, snoring occurs in combination with breath holding, gasping, or choking.

## Classification

In the International Classification of Sleep Disorders third edition (ICSD-3), snoring is listed under "Isolated symptoms and normal variants" in the section "Sleep-related breathing disorders". The manual defines snoring as "a respiratory sound generated in the upper airway during sleep that typically occurs during inspiration but may also occur in expiration."
Primary snoring (also termed simple snoring, non-apneic snoring, habitual snoring, or isolated snoring) is snoring without any other associated medical condition. Primary snoring is not associated with episodes of sleep apnea, hypopnea, respiratory-effort related arousals, or hypoventilation. There are no significant effects for the individual (such as daytime sleepiness or insomnia) or for a sleeping partner, although primary snoring may wake the individual or their sleeping partner. However, the idea that primary snoring without sleep apnea has no effects on quality of life is increasing challenged. For example, there is evidence that non apneic snoring, which is not associated with any sleep-related breathing disorder, causes excessive daytime sleepiness.
Therefore, primary snoring cannot be diagnosed in the presence of sleep apnea. Snoring is one of the main symptoms of obstructed sleep apnea, where it may be termed apneic snoring. In obstructed sleep apnea, snoring occurs in combination with other features such as breath holding (breathing cessation), gasping, or choking. There are also other features like daytime sleepiness, nonrestorative sleep, fatigue, or insomnia.
Snoring has been classified according to apnea–hypopnea index score and severity of associated sleep disorders. Therefore, snoring as a symptom exists as a spectrum of severity, with primary snoring being the least severe, snoring with upper airway resistance syndrome being of intermediate severity, and snoring associated with obstructive sleep apnea being the most medically significant.
* Asymptomatic, non-apneic snoring (primary snoring). No daytime sleepiness and apnea–hypopnea index less than 5 per hour.
* Non-apneic snoring with upper airway resistance syndrome. Daytime sleepiness and apnea–hypopnea index less than 5 per hour. Between 5 and 10 respiratory-effort-related arousals per hour. Oxygen saturation more than 90%.
* Apneic snoring (snoring associated with obstructive sleep apnea). Apnea–hypopnea index more than 5 per hour. Oxygen saturation less than 90%. Deviating pattern on electroencephalogram.
Primary snoring is occasionally defined as apnea-hypopnea less than 15 (or less than 10) with body mass index less than 32 kg/m$^2$. It has been suggested that individuals with primary snoring may gradually progress towards obstructive sleep apnea as causative factors such as aging and obesity change over time. However, there is limited evidence for this. 37% of children with primary snoring progressed to obstructive sleep apnea after 4 years. On the other hand, in many cases snoring is resolved over time rather than getting worse.
Snoring severity has also been classified according to average maximum volume:
* Mild (40-50 decibels)
* Moderate (50–60 dB)
* Severe (>60 dB)
In snoring associated with obstructive sleep apnea, louder snoring is correlated with severity of sleep apnea. On average, males snore more loudly than females, and people with higher body mass index snore louder than those with lower body mass index.

## Mechanism

Snoring occurs during sleep and is the result of the vibration of tissues along the upper respiratory tract or aerodigestive tract, such as the uvula, soft palate, faucial pillars (palatoglossal arch, palatopharyngeal arch), tonsils, walls of the pharynx, epiglottis, or lower structures. These tissues can relax enough to partially block the airway, resulting in irregular and reduced airflow and vibrations. The snoring sound mainly occurs during inspiration (breathing in), but it may occur during expiration (breathing out). On polysomnography, snoring is usually louder during stage N3 sleep or rapid eye movement sleep. Snoring has been mathematically modelled wherein the upper airway has a segment which is an elastic or collapsible tube. As the section of the upper airway narrows, resistance to the flow of air increases, and vibrations occur. Snorers have more negative pressure in their airway, increased inspiratory time, and limitation of respiratory flow. The airflow is unstable, turbulent and causes vibration of certain structures along the airway.

## Causes

Snoring can be attributed to one or more of the following:
* Genetic predisposition, a proportion of which may be mediated through other heritable lifestyle factors such as body mass index, smoking and alcohol consumption.
* Throat weakness, causing the throat to close during sleep.
* Mispositioned jaw, often caused by tension in the muscles.
* Obstruction in the nasal airway,
* Obstructive sleep apnea.
* Relaxants such as alcohol or other drugs relaxing throat muscles.
* Sleeping on one's back, which may result in the tongue dropping to the back of the mouth.
* Mouth breathing
* Pregnancy.
* Micrognathia (small jaw size).

### Obesity

Being obese or overweight increases the amount of fat around the throat. It is not just body mass index that is important, but the circumference of the neck and the size of the tongue.

### Alcohol

Alcohol causes muscle relaxation via its depressant effect on the central nervous system. This muscle relaxation seems to be more pronounced for the tongue, which may then be more prone to obstruct the airway.

### Muscle relaxants

Medications that cause muscle relaxation such as sedatives and hypnotics may cause snoring or make it worse. One example is diphenhydramine.

### Adenotonsillar hypertrophy

Adenoid hypertrophy (enlargement of the adenoid tonsil) and tonsillar hypertrophy (enlargement of the palatine tonsils) is associated with snoring and obstructive sleep apnea, especially in children since the tonsils are larger at younger ages.

### Dental problems

Dental problems may be conditions associated with snoring rather than direct causes. Examples include malocclusion, crowding of upper teeth, narrow palate, and high-arched palate.

## Possible consequences
### For sleeping partner

It is sometimes suggested that snoring is more of a problem for the sleeping partner than the person who snores. Snorers may be unaware of the their snoring. It may be difficult for sleeping partners to adjust to the noise because snoring may be irregular, changing in volume and character. This may wake them and prevent them from falling asleep again. Sleeping partners may try to nudge the snorer. This may trigger the snorer to change position, or it may rouse them sufficiently to reduce the muscle relaxation in the upper airway, lessening the snoring.
In one study, treatment of snoring in males (with continuous positive airway pressure) resulted in 13% better sleep efficiency and an average of 1 hour of extra sleep for their female sleeping partners. 1 hour of lost sleep per day equates to a whole night of lost sleep each week. This may result in chronic sleep deprivation for sleeping partners of snorers.
It has also been reported that sleeping partners of snorers may gradually develop hearing loss, although there is little evidence for this. In one small study, sleeping partners had detectable hearing loss in the ear that was habitually facing the snorer.
Parents of children who snore may also suffer reduced sleep quality.

### Cognitive and psychological

Snoring is known to cause sleep deprivation to snorers and those around them, as well as irritability, lack of focus and decreased libido. It has also been suggested that it can cause significant psychological and social damage to those affected. Though snoring is often considered a minor condition, snorers can sometimes experience severe impairment of lifestyle. Snoring, even when not associated with obstructive sleep apnea, has been linked to excessive daytime sleepiness.
In children, snoring may affect growth. It may also affect mood, attention, intelligence, and reduce academic performance at school, Snoring may manifest as behavioral problems.

### Cardiovascular disease

Some studies report that there is a higher prevalence of cardiovascular disease in snorers. This includes hypertension (high blood pressure), stroke, and ischemic heart disease. There may be up to a 46% increased risk of stroke. However, not all studies report increased risk of cardiovascular disease in those who snore. Snoring that starts during pregnancy may be linked with higher risk of gestational hypertension and preeclampsia.
There is limited evidence that snoring may cause atherosclerosis of the carotid artery. In research on animals, vibration energy from snoring may be transmitted to the carotid artery. This vibration causes damage to the endothelium. The binding ability of low density lipoprotein may also be increased by acoustic waves. Both non apneic snoring and snoring associated with obstructive sleep apnea have been correlated with carotid atherosclerosis, carotid artery stenosis, and other carotid disease in humans. In one study, snorers had 50% higher chance of carotid stenosis and were more likely to have carotid disease on both the left and right sides.

### Other

Nerve damage may occur in the soft palate as a result of chronic trauma from vibration. This is leads to morphological changes in the palate. Snoring is also linked to headaches and migraines, especially headache upon waking. This may be related to cerebral hypoxia, hypercapnia, and temporary increased intra-cranial pressure. Snoring is associated with respiratory event-related arousals, which may be connected with headache.
Snoring and obstructive sleep apnea are associated with higher rates of gastroesophageal reflux disease, including acid reflux which occurs during sleep. There is increased negative pressure in the thoracic cavity during apneic episodes. It was suggested that this negative pressure may overcome the lower esophageal sphincter and allow stomach contents to reflux into the esophagus. However, the lower esophageal sphincter was found to be stronger during obstructed breathing events. Another theory which explains the connection is that snoring and obstructive sleep apnea may promote transient lower esophageal sphincter relaxations. Enlarged tonsils are also seen in gastroesophageal reflux disease, and this may contribute to airway restriction and snoring.
There is conflicting evidence for and against a possible connection between snoring and sleep bruxism (teeth grinding during sleep). It may be that in snoring and obstructive sleep apnea, there are periods of activation of oropharyngeal muscles. These are necessary to restore patency of the collapsed / obstructed airway. This muscle activity may also trigger activity in the muscles of mastication and hence sleep bruxism.
There is limited and contradictory evidence for a connection between snoring and xerostomia (dry mouth). Tissue biopsies of the uvula have been carried out on heavy snorers and people with severe obstructive sleep apnea. The biopsies showed abnormal minor salivary glands. There was increased volume of mucous salivary glands and reduced quantity and volume of serous salivary glands. This may cause reduced production of saliva.

## Diagnosis

Primary snoring may only be diagnosed when obstructive sleep apnea has been ruled out. This usually requires a sleep study. Bronchoscopy may also be carried out. Questioning of not just the snorer but also their sleeping partner may be useful in the diagnostic process. An audio recording of the snoring may also be useful.
Palatal snoring (caused by vibration of the soft palate) has an average peak frequency of 137 hertz. Snoring caused by the tongue base has 1243 Hz. Combined palatal and tongue snoring has 190 Hz. Snoring caused by epiglottis has 490 Hz.

## Treatment

So far, there is no certain treatment that can completely stop snoring. Almost all treatments for snoring revolve around lessening the noise and improving air flow by reducing the blockage in the airway.

### Lifestyle modification

Lifestyle changes are a first-line treatment to stop snoring. Recommended lifestyle changes include stopping smoking, avoiding alcohol before bedtime, and sleeping on the side. Losing weight reduces the amount of fat that compresses the airway. Even a modest amount of weight loss, such as 4.5 kg (10 lbs) can improve snoring.
A number of other treatment options are also used to stop snoring. These range from over-the-counter aids such as nasal sprays, nasal strips or nose clips, lubricating sprays, oral appliances and "anti-snore" clothing and pillows, to unusual activities such as playing the didgeridoo. Many over-the-counter snoring treatments, such as stop-snoring rings or wrist-worn electrical stimulation bands, have no scientific evidence to support their claims.
Improving sleep hygiene may be beneficial. Examples include establishing fixed routines for bedtime and wake up time, including on weekends. Relaxation before sleep may help people get to sleep more quickly. Applications for smartphones and smartwatches are available. They often record snoring during sleep, compare snoring severity over time, and give advice to users. Some apps trigger a sound or vibration when the person starts to snore.

### Medications

Medications are usually not helpful in treating snoring symptoms, though they can help control some of the underlying causes such as nasal congestion and allergic reactions. Corticosteroid nasal sprays can reduce inflammation in nasal mucosa and reduce the size of the adenoid, thereby reducing symptoms of obstructive sleep apnea such as snoring. Montelukast has also been used in the same application.
Medications that aggravate snoring such as sedatives may be avoided before bedtime, or they may be substituted for weaker alternatives.

### Tongue exercises

Myofunctional therapy, which incorporates oropharyngeal and tongue exercises, reduces snoring in adults based on both subjective questionnaires and objective sleep studies. Snoring intensity was reduced by 51%.

### Orthopedic pillows

Orthopedic pillows are the least intrusive option for reducing snoring. These pillows are designed to support the head and neck in a way that ensures the jaw stays open and slightly forward. This helps keep the airways unrestricted as possible and in turn leads to a small reduction in snoring.

### Orthodontic treatment

Orthodontic treatment may improve some dental problems associated with snoring, such as a narrow palate.

### Dental appliances

Specially made dental appliances called mandibular advancement splints, which push the lower jaw slightly forward and thereby pull the tongue forward, are a common mode of treatment for snoring. Such appliances have been proven to be effective in reducing snoring and sleep apnea in cases where the apnea is mild to moderate. Mandibular advancement splints are often tolerated much better than CPAP machines.

### Positive airway pressure

A continuous positive airway pressure (CPAP) machine is often used to control sleep apnea and the snoring associated with it. It is a relatively safe medical treatment. To keep the airway open, a device pumps a controlled stream of air through a flexible hose to a mask worn over the nose, mouth, or both. A CPAP is usually applied through a CPAP mask which is placed over the nose and/or mouth. The air pressure required to keep the airway open is delivered through this and it is attached to a CPAP machine which is like an air compressor.
The air that CPAP delivers is generally "normal air"—not concentrated oxygen. The machine utilizes the air pressure as an "air splint" to keep the airway open. In obstructive sleep apnea, the airway at the rear of the throat is prone to closure.

### Surgery

Surgery is also available as a method of correcting social snoring. Some procedures, such as uvulopalatopharyngoplasty, attempt to widen the airway by removing tissues in the back of the throat, including the uvula and pharynx. These surgeries are quite invasive, however, and there are risks of adverse side effects. The most dangerous risk is that enough scar tissue could form within the throat as a result of the incisions to make the airway more narrow than it was prior to surgery, diminishing the airspace in the velopharynx. Scarring is an individual trait, so it is difficult for a surgeon to predict how much a person might be predisposed to scarring. Currently, the American Medical Association does not approve of the use of lasers to perform operations on the pharynx or uvula.
Radiofrequency ablation (RFA) is a relatively new surgical treatment for snoring. This treatment applies radiofrequency energy and heat (between 77 °C and 85 °C) to the soft tissue at the back of the throat, such as the soft palate and uvula, causing scarring of the tissue beneath the skin. After healing, this results in stiffening of the treated area. The procedure takes less than one hour, is usually performed on an outpatient basis, and usually requires several treatment sessions. Radiofrequency ablation is frequently effective in reducing the severity of snoring, but often does not eliminate it.
Bipolar radiofrequency ablation, a technique used for coblation tonsillectomy, is also used for the treatment of snoring.
Adenoidectomy or tonsillectomy (or combined removal, termed adenotonsillectomy) may be indicated if enlargement of the palatine tonsils or the adenoid tonsil is the cause of snoring, especially in children.

### Pillar procedure

The pillar procedure is a minimally invasive treatment for snoring and obstructive sleep apnea. In the United States, this procedure was approved by the FDA in 2004. During this procedure, three to six+ Dacron (the material used in permanent sutures) strips are inserted into the soft palate, using a modified syringe and local anesthetic. While the procedure was initially approved for the insertion of three "pillars" into the soft palate, it was found that there was a significant dosage response to more pillars, with appropriate candidates. As a result of this outpatient operation, which typically lasts no more than 30 minutes, the soft palate is more rigid, possibly reducing instances of sleep apnea and snoring. This procedure addresses one of the most common causes of snoring and sleep apnea—vibration or collapse of the soft palate (the soft part of the roof of the mouth). If there are other factors contributing to snoring or sleep apnea, such as conditions of the nasal airway or an enlarged tongue, it will likely need to be combined with other treatments to be more effective.

## Epidemiology

Statistics on snoring are often contradictory, but at least 30% of adults and perhaps as many as 50% of people in some demographics snore. One survey of 5,713 American residents identified habitual snoring in 24% of men and 13.8% of women, rising to 60% of men and 40% of women aged 60 to 65 years; this suggests an increased susceptibility to snoring with age. Snoring affects about 8–12% of children.
An observational study in the UK Biobank estimated that ~37% of 408,317 participants were habitual snorers, and confirmed positive associations with larger body-mass index, lower socio-economic status and more frequent smoking and alcohol consumption.

## Society and culture

There are descriptions of snoring in the fifteenth century. "Zzz" is a common onomatopeic representation of snoring. It may have developed from use in comics.
Snoring is sometimes not considered as a medical condition by medical insurance companies, meaning that treatments may not be covered by insurance.