In croup (medically known as laryngotracheitis), the upper airways become inflamed and narrowed, producing hoarseness, a harsh, grating sound while breathing in (known as stridor), a distinctive barking cough, and sometimes breathing difficulty.
Croup is most common in infants and young children and is usually caused by a viral infection of the airways, although it may also occur as a result of an allergy, inhaling a small foreign body or an irritant chemical, or epiglottitis (inflammation of the epiglottis, which is the flap of tissue behind the tongue that stops food from entering the airways).
Mild cases of croup may be treated with medication. Severe cases with serious breathing difficulty need urgent medical treatment.