Croup is breathing difficulty accompanied by a "barking" cough. Croup, which is swelling around the vocal cords, is common in infants and children and can have a variety of causes.

Viral croup is the most common. Other possible causes include bacteria, allergies, and inhaled irritants. Acid reflux from the stomach can trigger croup.

Croup is usually (75 percent of the time) caused by parainfluenza viruses, but RSV, measles, adenovirus, and influenza can all cause croup.

Before the era of immunizations and antibiotics, croup was a dreaded and deadly disease, usually caused by the diphtheria bacteria. Today, most cases of croup are mild. Nevertheless, it can still be dangerous.

Croup tends to appear in children between 3 months and 5 years old, but it can happen at any age. Some children are prone to croup and may get it several times.

In the Northern hemisphere, it is most common between October and March, but can occur at any time of the year.

In severe cases of croup, there may also be a bacterial super-infection of the upper airway. This condition is called bacterial tracheitis and requires hospitalization and intravenous antibiotics. If the epiglottis becomes infected, the entire windpipe can swell shut, a potentially fatal condition called epiglottitis.

Croup features a cough that sounds like a seal barking. Most children have what appears to be a mild cold for several days before the barking cough becomes evident. As the cough gets more frequent, the child may have labored breathing or stridor (a harsh, crowing noise made during inspiration).

Croup is typically much worse at night. It often lasts 5 or 6 nights, but the first night or two are usually the most severe. Rarely, croup can last for weeks. Croup that lasts longer than a week or recurs frequently should be discussed with your doctor to determine the cause.

Children with croup are usually diagnosed based on the parent's description of the symptoms and a physical exam. Sometimes a doctor will even identify croup by listening to a child cough over the phone. Occasionally other studies, such as x-rays, are needed.

A physical examination may show chest retractions with breathing. Listening to the chest through a stethoscope may reveal prolonged inspiration or expiration, wheezing, and decreased breath sounds.

An examination of throat may reveal a red epiglottis. A neck x-ray may reveal a foreign object or narrowing of the trachea.