The first indication is a cough that sounds like the bark of a dog or seal. Your child may have trouble breathing because the tissue around the larynx is inflamed, constricting the windpipe, and because the bronchial passages are blocked with mucus. The sound of air being forced through the narrowed airways may produce a hollow, raspy noise called stride, with each inhaled breath. However, there tends to be no similar sound with exhalation, as in wheezing.
Croup will generally last five or six days. It is highly contagious to other children who have not had the condition. It usually affects children between the ages of six months and three years, whose small windpipes and bronchial passages are most vulnerable to blockage. Children over six can get croup, though it is unusual. It is rare in babies under six months.