Most cases of croup do go away on their own without medical treatment.
However it's best to treat croup because although croup is rarely serious it can sometimes send your baby to the hospital.
If the croup is a mild case of croup then it will go away on it's own within a week but if not then your child has a more serious form of croup and should see a doctor for treatment.
In more severe cases of croup your baby or child with the croup may have difficulty breathing and coughing and in those cases take the baby or child to the doctor or the emergency room especially if they are having trouble breathing.
Croup can sometimes get worse before it gets better but if the child is having trouble breathing they need to get medical attention.
Using a humidifier to add moisture to the air the baby breathes can help with the croup.