There is another type of croup that can be activated by an infection while not being caused by one. This is known as spasmodic croup, and it can be quite similar to the infection-based forms of croup since they share many symptoms, such as a barking cough. However, the spasmodic infection sets in suddenly, presenting without a fever. It can be caused by an allergic reaction and most commonly occurs in children who range between three months and three years old. Infectious crop, on the other hand, more frequently presents itself in children up to six years old.