Croup refers to a group of conditions involving inflammation of the upper airway amongst children under 6 that leads to a cough that sounds like a bark. The majority of croup cases are caused by viruses, but some can be due to bacterial infection of an allergic reaction. It most commonly occurs in the fall, winter and early spring. The severity of the condition can vary dramatically; the methods of treatment are correspondingly diverse. While some cases need little attention, other rare forms can be life-threatening.