At times, though this is a rare scenario, croup maybe caused as a result of acid reflux, a condition where acid from the stomach leaks to the throat.

In some cases, severe croup conditions may develop due to allergic reactions to pollen grains or dust mites. Hence, it is important to maintain a hygienic, dust free environment in the home. Also, be cautious while taking the child on walks. He or she should be well protected with respiratory masks so as to deter inhalation of any environmental irritants.

Since croup is contagious, it can be spread by either inhaling infected mucous droplets in the air, coming in close contact with people infected with the disease, or while playing with and touching objects that may already be infected.

Occasionally, bacteria like Mycoplasma pneumonia, that cause pneumonia, can also cause croup in small children.

Sometimes, when children have not been immunized against measles, even the measles virus can cause acute croup conditions. Rare cases of chicken pox virus causing croup have also been diagnosed.

Besides Parainfluenza, the viruses that can cause croup include Influenza A and Influenza B. These are mainly flu viruses such as Rhinovirus, Adenovirus, Respiratory Synctial virus or RSV that cause severe breathing problems accompanied with pneumonia in babies.

Since croup is primarily a viral infection, it may either be caused by any of the three viral strains; Parainfluenza I, Parainfluenza II or Parainfluenza III. However, Parainfluenza I is the main culprit and about 80% of croup cases occur because of it.