There are many causes of stridor. Anything that causes the airway to be narrowed or partially blocked can cause stridor. Because of their smaller airways, stridor is more common in children than adults. The noisy sound is heard as air passes by the blocked or narrowed part of the voice box (larynx) or the windpipe (trachea).
When an infant is born with stridor, it is called a congenital disorder. This can be caused by:
- Laryngomalacia: Parts of the voice box are floppy and collapse as a child breathes in. This partially blocks air movement. This is the most common congenital cause of stridor in children. Most children with laryngomalacia grow out of it by 18 months of age.
- Vocal cord paralysis: There are two vocal cords above the windpipe that are used to make sound. Paralysis means one or both do not move.
- Subglottic hemangioma: This is a mass formed from abnormal blood vessels that can grow in the airway. It is a very rare condition.
When a child develops stridor later in life, it is called an acquired disorder. This can be the result of infection or trauma.
- Croup: This is an infection caused by a virus that results in swelling of the airways.
- Epiglottitis: This is a severe life-threatening infection of the epiglottis (the small lid that closes over windpipe when swallowing). It is caused by bacteria. The swelling of the epiglottis can worsen over time and make it hard or impossible to move air into the lungs. Epiglottitis is rare because infants have routine vaccination for the bacteria that commonly causes the infection (Haemophilius influenza).
- Tonsillitis: This is an infection of the tonsils (soft tissue in the back of mouth) that can cause the tonsils to get big and swollen. In severe cases it can cause noisy breathing.
- Foreign body: A foreign body is an object that is swallowed or inhaled. This can cause a blockage of the airway. This may result in stridor and trouble breathing. If the object is in the airway, this is an emergency.
- Swallowing a harmful material may cause injury to the airway or the esophagus (swallowing tube).
- Injury to the neck.