Stridor is a high-pitched sound that is usually heard best when your child breathes in (known as “inspiration”). It’s usually caused by an obstruction or narrowing in your child's upper airway.

  • The exact sound of stridor depends on location of the obstruction.
  • Sometimes, stridor is heard when your child breathes in and when she breathes out.
  • Children’s upper airways are shorter and narrower than those of adults and, therefore, more likely to lead to problems with obstruction.

At Boston Children's Hospital, the Center for Airway Disorders (CAD) provides care and state-of-the-art medical and surgical treatment to children with stridor and other problems involving the airway, pulmonary, and upper digestive tract. The center is staffed by a multidisciplinary team of specialists from various fields who provide comprehensive assessment, treatment, and follow-up care.

What is the upper airway?

The upper airway is made up of the following structures in the upper respiratory system:

  • nose
  • nasal cavity: a large, fluid-filled space above and behind the nose
  • ethmoidal air cells: a cavity (space) located near the eyes and the back of the nose
  • larynx (voicebox): a cylindrical grouping of cartilage, muscles, and soft tissue that contains the vocal cords. The vocal cords are the upper opening into the trachea.
  • trachea (windpipe): a tube that reaches from the voice box to the bronchi in the lungs.
  • sinuses: cavities, or air-filled pockets, that are near the nasal passage. They help the nose filter the air by producing mucus, which traps dust and bacteria before they can reach the lungs.

The sinuses include:

ethmoid sinus
inside the face, around the bridge of the nose
present at birth and continues to grow
maxillary sinus
inside the face, around the cheeks
present at birth and continues to grow
frontal sinus
inside the face, in the area of the forehead
does not develop until around 7 years of age
sphenoid sinus
deep in the face, behind the nose
does not develop until adolescence

What causes stridor?

There are many different causes of stridor. A disease may cause stridor, but so may a problem with the anatomical structure of your child's airway. The following are some of the more common causes of stridor in children:

Congenital causes (problems present at birth)

Congenital causes (problems present at birth):

  • Laryngomalacia: Parts of the larynx are floppy and collapse, causing partial airway obstruction.
    • If your child has laryngomalacia, she will probably outgrow this condition by the time she is 18 months old.
    • Some children may need surgery.
  • Subglottic stenosis: The larynx (voice box) may become too narrow in a spot called the cricoid cartilage.
    • If your child has subglottic stenosis, she will usually be diagnosed a few months after she is born, particularly if her airway becomes stressed by a cold or other virus.
    • She may eventually outgrow this problem without intervention.
    • If the obstruction is severe, she will most likely need a surgical procedure.
  • Subglottic hemangioma: This is a type of mass that consists mostly of blood vessels.
    • A subglottic hemangioma would grow quickly in your child's first few months of life, and she would usually show symptoms around the age of 3 to 6 months.
    • Some children may outgrow this problem, as the hemangioma will begin to shrink after the first year of life.
    • Most children will need surgery if the obstruction is severe.
  • Vascular rings: The trachea may be completely enclosed by another structure, like an artery or vein. If your child has this condition, she may require surgery.
Infectious causes
  • Croup: Croup is an infection that leads to swelling in the airways and causes breathing problems. It may be caused by a variety of different viruses, most commonly the parainfluenza virus.
  • Epiglottitis: This is an acute (may come on suddenly) life-threatening bacterial infection that results in swelling and inflammation of the epiglottis (an elastic structure at the root of the tongue that prevents food from entering the windpipe when swallowing).
    • It causes breathing problems that may get worse and ultimately lead to so much swelling that air cannot get in or out of the lungs, resulting in a medical emergency.
    • Epiglottitis is usually caused by the bacteria Haemophilus influenzae, and is now rare because children are routinely vaccinated against this bacteria.
  • Bronchitis: This is an inflammation of the breathing tubes (airways), called bronchi, which causes increased production of mucus and other changes.
    • Acute bronchitis is usually caused by infectious agents, such as bacteria or viruses, but may also be caused by physical or chemical agents — dusts, allergens, strong fumes — and those from chemical cleaning compounds, or tobacco smoke.
  • Severe tonsillitis: The tonsils are small, round pieces of tissue that are located in the back of the mouth on the side of the throat. Tonsillitis is defined as inflammation of the tonsils from infection.
    • Tonsils are thought to help fight infections by producing antibodies.
    • The tonsils can usually be seen in the throat of your child by using a light.
  • Abscess in the throat:  An abscess in the throat is a collection of pus surrounded by inflamed tissue. If the abscess is large enough, it may narrow the airway to a critically small opening.
Traumatic causes

Traumatic causes:

  • foreign bodies — any objects placed in the ear, nose or mouth that do not belong there
  • fractures in the neck
  • swallowing a harmful substance may cause damage to the airways