Stridor is a high-pitched, harsh, strained sound that occurs when air forces its way through a narrowed airway. It has a distinctly musical quality, almost like a single sustained note, which separates it from other noisy breathing patterns. The pitch typically falls around 190 Hz on average, roughly equivalent to the G below middle C on a piano, though it varies between individuals. If you’ve ever heard someone breathe through a tightly pinched straw, that forced, squealing quality is close to what stridor sounds like.
The Key Sound Qualities
Stridor is produced when airflow becomes turbulent as it passes through a tight spot in the upper airway, near the vocal cords or just above or below them. Because the vocal cords are involved in generating the sound, stridor contains harmonics and overtones, giving it a tonal, almost musical character. This is what makes it sound so different from ordinary noisy breathing. The sound can be rhythmic and steady, with a consistent pitch and volume on each breath, or it can be more irregular, fluctuating in intensity.
The word most commonly used to describe stridor is “harsh.” It’s loud enough to hear from across a room in many cases, and it sounds effortful, like the person is working hard to pull air through a narrow opening. In children with croup, the breathing often has a seal-like barking quality alongside the stridor, which parents sometimes describe as alarming even before they know the medical term for it.
Stridor vs. Wheezing vs. Snoring
These three sounds get confused often, but they come from different parts of the airway and have distinct characteristics.
- Stridor is a high-pitched, musical sound originating in the upper airway (throat and voice box area). It’s loudest over the neck rather than the chest, and it typically occurs when breathing in.
- Wheezing is a whistling sound produced by narrowed small airways deep in the lungs, like the kind seen in asthma. Wheezing is loudest during breathing out and is best heard with a stethoscope over the chest.
- Stertor is a low-pitched grunting or snoring sound, loudest during breathing in. In children, it’s usually caused by enlarged tonsils or adenoids. Think of the sound a child makes when sleeping with a stuffy nose: that rumbling, congested quality is stertor, not stridor.
The easiest way to tell them apart: stridor is high and squeaky, wheezing is a lower whistle, and stertor sounds like snoring.
When in the Breath It Happens Matters
One of the most important things about stridor is when it occurs during the breathing cycle, because this reveals where the airway is blocked.
Stridor that happens only when breathing in (inspiratory stridor) points to an obstruction at or above the vocal cords. This is the most common type. During inhalation, the pressure inside the airway drops below the surrounding air pressure, which can cause a floppy or swollen structure near the vocal cords to get sucked inward and partially block airflow.
Stridor heard only when breathing out (expiratory stridor) suggests the blockage is lower, in the windpipe itself. During exhalation, rising pressure in the chest compresses the airway at the point of narrowing. The most common cause of this pattern in children is tracheomalacia, a condition where the windpipe walls are too soft and collapse during exhalation.
Biphasic stridor, heard on both inhaling and exhaling, typically means the narrowing is right at or just below the vocal cords. Viral croup is the most common cause of biphasic stridor in children.
Common Causes in Children and Adults
In infants, the most frequent cause of stridor is laryngomalacia, a condition where the soft tissue above the vocal cords is floppy and collapses inward with each breath. This produces a fluttery, high-pitched inspiratory sound that often gets louder when the baby is feeding, crying, or lying on their back. Most babies with laryngomalacia outgrow it within the first 12 to 18 months of life.
In toddlers and young children, croup is the classic cause. The hallmark is a barky cough that sounds remarkably like a seal, combined with stridor that may be present only when the child is upset or active (mild cases) or audible even at rest (more concerning). Croup scoring systems actually use this distinction: stridor that appears only with agitation is considered mild, while stridor at rest indicates moderate to severe illness.
In adults, stridor is less common and more likely to signal a serious problem. Vocal cord paralysis is one of the more frequent causes, and it can result from nerve damage during thyroid surgery, compression by tumors in the chest or neck, or lung cancer pressing on the nerve that controls the vocal cords. Bronchogenic carcinoma (lung cancer) is the single most common tumor type causing this nerve compression. Adults may also develop stridor from allergic reactions causing throat swelling, or from scarring in the airway after prolonged intubation.
Mild Stridor vs. an Emergency
Not all stridor is equally dangerous, but it always signals some degree of airway narrowing that deserves attention. The severity depends on how much the airway is compromised and how hard the body is working to compensate.
Mild stridor may only be noticeable when a child is crying, coughing, or physically active. Breathing is otherwise comfortable, and the child can eat, drink, and speak normally. Many cases of croup fall into this category and can be managed at home.
Moderate stridor is audible at rest and comes with visible signs of extra effort: you can see the skin pulling in between the ribs or above the collarbones with each breath (called retractions), and breathing is noticeably faster than normal.
Several signs indicate the situation is becoming dangerous. Drooling, especially combined with agitation, suggests the swelling is severe enough that the person can’t swallow their own saliva. Leaning forward in a “tripod” position with hands on knees and chin jutting out is an instinctive attempt to open the airway as much as possible. Bluish discoloration of the lips or fingertips means oxygen levels have dropped significantly. A decreasing level of alertness, difficulty speaking, or a look of air hunger, where the person appears panicked and is straining to breathe, all signal that the airway obstruction is critical. Paradoxically, stridor that suddenly becomes quieter in someone who was struggling to breathe can mean the airway has narrowed so much that not enough air is moving to produce sound.