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What is stridor or wheezing?


What is wheezing?

Stridor, also known as wheezing, is a breathing sound which is caused by a narrowing of the respiratory tracts. It may be a whistling or hissing sound. Normally, unhindered breathing is silent. Audible air turbulence occurs when there is an obstacle in the respiratory tracts.

Stridor may have a variety of causes. In babies and children, stridor develops relatively quickly as their respiratory tracts are narrower and more elastic than in adults. Stridor in children is generally temporary and harmless in nature.

Inspiratory stridor, expiratory stridor, biphasic stridor

Doctors distinguish between inspiratory stridor during inhalation and expiratory stridor during exhalation. Biphasic stridor is observed both during inhalation and exhalation.

Inspiratory stridor occurs when the trachea, larynx or pharyngeal cavity are constricted.

Expiratory stridor usually is caused by constrictions in the bronchi.

Stridor: Causes and possible diseases

Causes of stridor in children

Respiratory tracts in babies and children are more elastic and significantly narrower than those in adults. Even a slight constriction may lead to respiratory sounds and most often originates in the trachea or pharynx. The cause of stridor in children and babies may be congenital or acquired.

Congenital causes of stridor in children

Laryngomalacia: A common congenital cause of stridor in children is laryngomalacia. During inhalation it results in a narrowing of the trachea. The stridor increases when eating and during periods of excitement or crying, and decreases when at rest and in the prone position. In most cases this stridor is harmless and does not constitute a disease. A doctor should be consulted in the case of very significant stridor.

Tracheomalacia: Stridor also occurs during a tracheomalacia. It occurs because the cartilage rods in the trachea are too soft.

Vocal cord paralysis: In infants, vocal cord paralysis also can occur, which severely hinders breathing and also leads to biphasic stridor.

Malformations: Malformations also can interfere with the infant's breathing and cause stridor.

Acquired causes of stridor in children

Acquired causes of stridor in children include:

  • Infections of the larynx and trachea
  • Croup
  • Inflammation of the epiglottis
  • Inflammation of the trachea
  • Allergic reactions
  • Inhaled foreign bodies

Stridor: Causes and possible diseases in adults

In adults, expiratory stridor is more common. The causes of stridor often are associated with the bronchi and the lungs.

The causes of expiratory stridor in adults often include diseases of the respiratory tracts, which make exhalation difficult:

  • Bronchial asthma
  • Chronic obstructive pulmonary disease (COPD)
  • Pulmonary emphysema (hyperinflation of the pulmonary alveoli)
  • Chronic or acute inflammation of the bronchi (bronchitis)
  • Less common: a tumour or lymphatic cancer that presses on the bronchi

Causes of inspiratory stridor

In adults, inspiratory stridor often has the following causes:

  • Enlargement of the thyroid
  • Inflammation in the throat
  • Foreign bodies in the throat
  • Allergic reaction
  • Damage after artificial respiration with intubation
  • Damage after throat surgery

Stridor: When should you visit the doctor?

Stridor is a symptom which may have many harmless causes. However, you should consult your doctor, as the respiratory distress may increase or even become life-threatening. In addition, stridor also could be indicative of a serious illness.

You should follow the instructions provided by your doctor or call an ambulance if acute respiratory distress occurs suddenly.


Treatment depends on the underlying cause. Stridor often is a harmless and temporary symptom.

Congenital malformations or respiratory tract tumours may require surgery.

In acute situations of stridor accompanied by shortness of breath,
immediate action must be taken.

Preventive measures against stridor

If you have respiratory problems, you should strictly follow guidelines provided with your prescribed medication to prevent a stridor.


Von Dr. med. Fabian Sinowatz