Causes and Risk Factors for Croup

In most cases, croup develops from a cold or flu virus. Common causes for croup include the following:

  • Adenoviruses (common cold viruses)
  • Human parainfluenza viruses (common cause for lower respiratory infections in children)
  • Influenza viruses (flu viruses)
  • Respiratory syncytial virus (RSV; common cause for bronchiolitis and pneumonia)
  • Rubeola virus (virus that causes measles)

In rare cases, a bacterial infection (e.g., Mycoplasma pneumoniae, Streptococcus pneumoniae [types of bacteria that can cause pneumonia]), allergy (e.g., pollen), or inhaled irritant (e.g., food particle) can cause croup.

Infants and children who were born prematurely (i.e., before 37 weeks), young children who have narrow upper airways, and children who have breathing conditions, such as asthma, are at increased risk for croup.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 27 Aug 2008

Last Modified: 10 Sep 2015