In some cases croup can be dangerous and lead to breathing difficulties so severe that it requires medical attention and an emergency room visit.
If croup gets serious enough the croup sometimes will cause the airway to swell so much that your child may barely be able to breathe.
In the more severe cases, your child will not be getting enough oxygen into her blood and when and If this happens, the child needs to go to the hospital.
However most cases of croup don't go that far but you still should be aware and if the child starts having more difficulty breathing take the child or the person with the croup to the emergency room right away for treatment or call 911 if needed.