If you experience a whistling sound while breathing, or have heard someone make it, and are wondering what may cause such a sound, look no further!

This article will break down the science behind what causes these sounds, how these sounds are triggered, and what it may mean for your health.

Introduction

The high-pitched breathing sound is often referred to as wheezing or stridoring. It occurs when the airflow through the respiratory tract is partially blocked.¹ This narrows the respiratory tract, leaving less room for air to move in which causes increased resistance in the lungs and turbulence in airflow.

When air moves rapidly through this partial blockage, it causes surrounding mucus and airway walls to vibrate, producing high-pitched sounds during breathing.² If the obstruction occurs in the upper airway, it is known as stridor, while blockage in the lower airway is called wheezing.^3,4

While these noises don’t usually hinder lifestyle, they can be an indication of underlying health problems that can lead to serious complications if left unaddressed. However, to understand how stridor and wheezing can be used to gauge health issues, we need to first understand how airflow works, why changes can occur in airflow, how it affects breathing, how affected breathing leads to the breathing sounds, and how all of these tie together to impact health.

The structure of the respiratory tract and how normal airflow occurs

The human respiratory tract is designed to move air efficiently from the environment into the lungs and back out again, with minimum resistance and noise.⁴

The cycle of breathing starts when breathing in: air enters the body through the nose (or the mouth), which serves as the entry point to the respiratory system. As air is inhaled through the nose, it is filtered, humidified, and warmed by the nasal passages.⁴ This is an essential process that protects the fragile lung tissues from irritants, dryness, or temperature extremes.

After the conditioning, air moves from the upper airways, travelling through the throat (specifically the pharynx), passing the voice box containing the vocal cords, and entering the windpipe (trachea).⁴ Under normal conditions, the structures in the upper airways are flexible and remain open to allow air to pass through without any obstruction and thus make no sound.

As the air moves into the trachea, it enters the lower respiratory tract located in the neck and upper chest. The trachea is a sturdy tube that is reinforced with cartilage rings. This tube branches into two bronchi, with each leading to one lung. Inside the lungs, these bronchi divide into further, smaller tubes called bronchioles that form a tree-like system inside the lungs.⁵

Bronchioles contain tiny air sacs called alveoli at the end of each branch, where oxygen is passed into the bloodstream while carbon dioxide is removed in a process called gas exchange.⁵ The process of gas exchange, as well as the entire process of gas exchange described above, occurs within seconds and repeats thousands of times each day, ensuring that the body is supplied with sufficient oxygen to carry out its usual activities.

What is laminar airflow, and why does it matter?

Laminar airflow means air moves in a smooth and efficient pattern without any obstruction.⁶ In a healthy person, airflow is usually laminar, meaning the air that is breathed is moved uninterrupted through open airways, moving from the upper respiratory tract to the lower respiratory tract and to the alveoli in the lungs where gas exchange occurs, and air containing carbon dioxide is expelled out of the body through breathing out.⁶

So, why is laminar airflow so important? Laminar flow is a highly efficient mechanism because it requires minimal effort from the muscles within the respiratory tract and produces little to no sound.^5,6 As such, in a healthy individual, breathing is usually silent when relaxed or accompanied by a faint rustling sound during deeper breaths.

Factors that maintain laminar airflow

Multiple factors help maintain a quiet and efficient breathing process, ensuring maximum air containing oxygen is supplied to the lungs while simultaneously, maximum carbon dioxide is expelled out of the lungs. Some of these factors and how they help laminar airflow are listed in the table below:^6,7

When the conditions above are met and maintained, the respiratory system operates efficiently, allowing breathing to be nearly silent and unnoticeable. However, if any part of the airflow mechanism is disrupted and any part of the respiratory system is damaged, laminar flow becomes turbulent, and breathing becomes audible.⁷

Factors such as inflammation, structural narrowing, or obstruction can cause laminar flow to be disrupted and lead to noisy breathing that eventually leads to stridor or wheezing.

What causes changes in the airways?

As mentioned above, there are many factors that disrupt airflow and lead to audible breathing. One of the most common causes of disrupted airflow is the narrowing of the respiratory tracts, also known as airway stenosis.⁷

Airway stenosis can occur due to many reasons, some of which are temporary, while others are permanent, and therefore a significant indicator of more serious issues.^6,7 Some of the most common issues leading to airway narrowing are listed below:

• Inflammation: Respiratory infections such as bronchitis can cause the lining of the respiratory tracts to swell, which reduces the diameter of the trachea and bronchi, causing airflow to be disrupted and become inefficient¹⁰
• Allergic reactions: Linked to inflammation, exposure to allergens such as pollen, dust mites, etc, can trigger allergic reactions that in turn trigger an inflammatory response in the body, leading to swelling that reduces the diameter of the tubes via which air travels. This is particularly evident in asthmatic individuals or individuals with allergic rhinitis¹⁴
• Bronchospasm: In certain conditions, such as asthma, the muscles lining the bronchi and bronchioles can suddenly contract, leading to the airway diameter being reduced, which increases resistance to airflow and traps air in the respiratory tracts¹⁴
• Structural issues: Congenital or acquired structural problems in the respiratory tract can reduce the space available for airflow. Conditions such as laryngomalacia (where the laryngeal tissue is soft and floppy) or subglottic stenosis (narrowing of the airway below the vocal cords) are examples of structural issues that can disrupt airflow and lead to noisy breathing. These are particularly problematic when occurring in infants and children

Not all airflow disruptions originate inside the airways. Sometimes external structures can press against part of the respiratory structures, causing them to be compressed externally.⁷ Some external compression factors are:

• Enlarged lymph nodes: Lymph nodes can grow in size due to infections, cancers, or autoimmune diseases. These enlarged structures can press against the trachea or bronchi, leading to external forces that essentially squeeze the respiratory tubes and reduce their diameter^{9, 10}
• Goitre: Goitre is the enlargement of the thyroid gland that is responsible for producing hormones. When the thyroid gland is enlarged, it can press against the trachea, leading to external pressure that reduces the airway diameter⁹
• Vascular abnormalities: Abnormalities such as a double aortic arch, where the aorta splits into two arches and forms vascular rings around the trachea and oesophagus, can lead to compression of the airway by creating unnecessary external pressure¹¹

While the most common, airway narrowing is not the only cause of disrupted airflow. Sometimes,  the obstruction of airflow can occur due to a physical blockage inside the airway.⁷ These obstructions can include:

• Build-up of mucus: Mucus is a slippery fluid that lines various parts of the body, including the respiratory tract. It can accumulate in the bronchioles and result in mucus plugs that can physically block air movement within the respiratory tracts. Build-up of mucus is common in chronic conditions like cystic fibrosis¹²
• Blood or pus: In cases of severe infections or trauma, blood may enter the airways and obstruct airflow. In cause of severe infections, it can lead to the formation of pustules, which can burst and lead to pus entering the airways and acting as a physical blockage⁹
• Tumoural growth: Both benign and malignant tumours can occur within the airways or intrude into the airways from surrounding tissues, leading to a physical mass that blocks the passage of air¹²
• Foreign objects: Inhaling small objects such as food particles or plastic molecules can partially or completely block the airway by creating a physical barricade. This is particularly a concern for toddlers because they can inhale or swallow small toys, leading to blockage of airways and, in the most severe cases, suffocation

When the airway narrows, the resistance to airflow increases. An increase in resistance requires more conscious effort to breathe and is the major contributor to abnormal sounds during breathing, which are a result of air being forced around or through the obstructions.

Why does narrowing of the airways cause noise?

As airflow is forced through narrowed or obstructed airways, it becomes turbulent. Instead of moving smoothly, air molecules collide with each other and with the airway walls. This chaotic movement generates vibrations, which are transmitted as sound waves through the tissues of the neck and chest, eventually reaching the ear.⁷

These noises can be differentiated into three main groups: 

• Inspiratory stridor: High-pitched sound heard during inhalation, caused by obstruction in the upper airway ( larynx or trachea)¹³
• Expiratory wheezing: Whistling noise during exhalation, resulting from narrowed lower airways, often seen in conditions like asthma or COPD^13,14
• Biphasic stridor: Harsh, high-pitched sound present during both inhalation and exhalation that indicates a fixed obstruction at the level of the vocal cords or subglottic area¹³

When to seek medical help?

Abnormal sounds during breathing may not often directly impact health, but if left unchecked, they can cause more severe consequences later down the line. As such, it is advised that medical advice be sought to ensure it is not a symptom of a more complicated disease. In particular, if the high-pitched breathing sounds are accompanied by:¹⁵

• Difficulty breathing
• Voice loss
• Rapid, unregulated breathing
• Drooling
• Difficulty swallowing

Then, it can be considered a sign of a medical emergency, and it is advised to seek immediate medical attention.

Treatment

Depending on the underlying condition and accompanying symptoms, there are specific treatment and management strategies.⁸ But, some general interventions can include:¹⁵

• Inhalers
• Steroids
• Surgical interventions
• Oxygen therapy
• Mechanical ventilation

Summary

High-pitched breathing sounds like stridor and wheezing result from changes in airflow due to narrowed or obstructed airways. These airflow disturbances create turbulent air movements that can cause vibrations that generate audible, high-frequency sounds. Understanding their location, timing, and cause is crucial for diagnosis and treatment. While sometimes temporary or harmless, these sounds often signal serious conditions that can require medical intervention.