Croup looks and sounds unmistakable once you’ve seen it: a child, usually between 6 months and 3 years old, sitting up in bed at night with a harsh, barking cough, labored breathing, and a high-pitched whistling sound each time they inhale. The child’s voice is hoarse, their chest may visibly pull inward with each breath, and they often look frightened, which makes everything worse. It’s one of the most recognizable childhood illnesses, affecting about 3% of children under 5 worldwide.
The Barking Cough
The hallmark of croup is a cough that sounds nothing like a normal cold. It’s deep, brassy, and hollow, often compared to a seal barking. Physicians have described it for centuries in colorful terms: the crowing of a rooster, the yelping of a fox, a sound “as if the voice came from a brazen tube.” In practice, most parents recognize it as a loud, almost metallic bark that seems to come from deep in the throat rather than the chest. It’s a dry, non-productive cough, meaning your child won’t be coughing up mucus.
Alongside the cough, you’ll likely hear stridor, a harsh, raspy, vibrating noise that happens when your child breathes in. One 19th-century physician likened it to the sound of someone badly playing a clarinet, producing “a harsh, squeaking sound abundantly discordant and grating to the ear.” In mild cases, stridor only shows up when your child is crying or upset. In more severe cases, it’s audible even at rest.
What You’ll See in Your Child’s Body
Beyond the sounds, croup has visible signs. The area just below the throat and between the ribs may suck inward each time your child tries to inhale. These are called retractions, and they happen because the child is working harder than normal to pull air through a narrowed airway. The more dramatic the retractions, the more significant the airway narrowing.
Your child’s voice will sound hoarse and raspy, sometimes barely above a whisper. They may sit upright or lean forward because that position makes breathing slightly easier. In mild cases, the child is alert and active between coughing episodes. In more serious cases, you might notice pale or bluish skin around the lips and fingernails, unusual sleepiness, or a child who seems too exhausted to cry. Those signs indicate the body isn’t getting enough oxygen and require immediate medical attention.
Why It’s Worse at Night
Most parents first encounter croup between 11 p.m. and 4 a.m. A child who seemed to have a mild cold during the day suddenly wakes with the barking cough and noisy breathing. This nighttime pattern is so consistent it’s practically a diagnostic clue on its own.
The exact reason isn’t fully understood, but the leading theory involves the body’s natural 24-hour hormone cycles. Cortisol, which helps reduce inflammation, drops to its lowest levels late at night and in the early morning hours. With less of this natural anti-inflammatory circulating, airway swelling peaks during those same hours. Cooler nighttime air and the fact that lying flat allows more fluid to pool around the already swollen airway tissue likely contribute as well. A child’s agitation upon waking up unable to breathe normally then triggers more swelling, creating a cycle that can escalate quickly.
What’s Happening Inside the Airway
Croup is caused by a viral infection (most often parainfluenza virus) that inflames the airway just below the vocal cords, in a region called the subglottis. In young children, this is the narrowest part of the airway, and even a small amount of swelling dramatically reduces the space available for air to pass through. A child’s windpipe at this point is roughly the diameter of a pencil, so a millimeter or two of swelling can cut airflow significantly.
That narrowing is what produces every symptom you see and hear. Air being forced through a tighter opening creates the stridor. The inflamed vocal cords produce the hoarse voice and barking cough. The child’s respiratory muscles work overtime to compensate, producing the visible chest retractions. If a doctor were to take an X-ray of the neck from the front, the swollen airway would appear as an inverted V shape, sometimes called a “steeple sign” because it resembles a church steeple tapering to a point.
How It Differs From More Serious Conditions
The barking cough is actually reassuring in one sense: it’s characteristic of croup and not of epiglottitis, a rarer but more dangerous infection of the flap that covers the windpipe during swallowing. Epiglottitis comes on suddenly and severely, with high fever and drooling, but typically without the barking cough. A child with epiglottitis looks sicker, often refusing to speak or swallow, and may sit in a “tripod” position leaning forward with their mouth open. Croup, by contrast, develops more gradually, usually starting with a day or two of cold symptoms before the distinctive nighttime cough appears.
Croup can also be confused with a foreign object lodged in the airway, which tends to cause sudden choking without the preceding cold symptoms, or with bacterial tracheitis, which produces a croup-like picture but with higher fevers and a child who looks significantly more ill.
Typical Timeline
Croup usually begins with one to two days of runny nose, mild fever, and a regular-sounding cough. The barking cough and stridor then emerge, typically peaking on nights two and three. Most children improve substantially within three to five days, though a mild cough can linger for about a week. The illness is self-limiting in the vast majority of cases.
The worst episodes tend to cluster in the first two or three nights. Many parents find that the second night is actually worse than the first, which can be alarming if they thought their child was improving during the day. Daytime symptoms are almost always milder, and some children seem nearly normal during waking hours only to have the cough return after bedtime.
How Severity Is Assessed
Doctors evaluate croup severity using five observable signs: the level of consciousness (alert versus drowsy), skin color changes suggesting low oxygen, the presence and intensity of stridor, how well air is moving in and out of the lungs, and how pronounced the chest retractions are. Mild croup means the barking cough is present but stridor only occurs with crying or agitation. Moderate croup involves stridor at rest and visible retractions. Severe croup adds signs like decreased consciousness, significant breathing difficulty, or color changes.
The vast majority of croup cases are mild. In the United States, croup accounts for roughly 7% of pediatric hospitalizations and up to 15% of emergency department visits for children under 5, but fewer than 3% of those hospitalized need any help breathing beyond a steroid medication to reduce the airway swelling.
What Treatment Looks Like
For mild croup at home, keeping your child calm is the single most effective thing you can do. Crying and agitation increase the effort of breathing and worsen stridor, which creates more fear, which causes more crying. Sitting with your child, speaking quietly, and offering comfort can break that cycle. Cool night air often helps, which is why many parents notice improvement during the car ride to the emergency room with the window cracked open.
When a child is seen by a doctor for croup, the standard treatment is a single oral dose of a steroid medication to reduce airway swelling. This works regardless of whether the croup is mild, moderate, or severe. There’s no evidence that a second dose adds benefit. For moderate to severe cases in the emergency department, an inhaled medication that rapidly shrinks swollen tissue may be given for faster relief while the steroid takes effect over the next few hours. Most children treated this way go home the same night or the following morning.