A condition of breathing difficulty caused by infection, inflammation, and swelling of the upper airway (larynx, trachea, andbronchus).Croup is characterized by a "barking" cough (sometimes described as a hoarse cough, or as a seal-bark cough); hoarseness(laryngitis) ; noisy, high-pitched breathing sounds when inhaling (stridor) ; and increasing difficulty in breathing.

Croup is usually caused by viral infection (parainfluenza virus, respiratory syncytial virus (RSV) , and influenza viruses A andB) which is present in the air around others with the infection. A bacterial infection leading to croup is most often caused byHemophilus influenza (epiglotitis, a life-threatening infection). Croup can also be caused by allergies, trauma, or foreign bodies(toys, peanuts, other small objects) in the airway. Croup most often occurs in children between 6 months and 3 years of age.The recognizable barking cough and noisy breathing (stridor) is caused by swelling in the upper airway (larynx, trachea, andbronchi). The child's breathing becomes more difficult and requires increasing physical effort. The child may be physicallytired but is unable to rest because of the increased breathing effort.The child may be restless, have a fever, and be working hard to keep breathing. Extra effort to breathe may be noticed as wideropening of the nasal openings during inhalation (nasal flaring) ; increased use of the muscles in the neck and chest; andunwillingness to lie down, rest, eat, or drink. In severe cases the child's lips and fingers may turn blue (cyanosis) , indicatinginadequate oxygen supply.See also epiglottitis.

Appropriate hygiene and avoiding closeness to or contact with others with respiratory infections can prevent some infections.Croup caused by a foreign object can be prevented by keeping small objects out of the reach of young children.