Croup is an inflammation of the vocal cords (larynx) and windpipe (trachea). It causes difficulty breathing, a barking cough, and a hoarse voice. The cause is usually a virus, often parainfluenza virus. Other causes include allergies and reflux.
Croup often starts out like a cold. But then the vocal cords and windpipe become swollen, causing the hoarseness and the cough. There may also be a fever and high-pitched noisy sounds when breathing. The symptoms are usually worse at night, and last for about three to five days. Children between the ages of 6 months and 3 years have the highest risk of getting croup. They may also have more severe symptoms. Croup is more common in the fall and winter.
Most cases of viral croup are mild and can be treated at home. Rarely, croup can become serious and interfere with your child's breathing. If you are worried about your child's breathing, call your health care provider right away.
Read more at: https://medlineplus.gov/croup.html