The hallmark symptom of croup is a harsh, barking cough that sounds like a seal. It typically strikes children between 3 months and 5 years old and results from swelling around the voice box, windpipe, and bronchial tubes. Most cases start with ordinary cold symptoms before the distinctive cough appears, often catching parents off guard in the middle of the night.
The Barking Cough
Croup’s signature sound is unmistakable once you’ve heard it. When a cough forces air through the narrowed, swollen airway, the vocal cords produce a loud, harsh bark. Parents often describe it as sounding like a seal or a dog. It’s dramatically different from a normal wet or dry cough, and it tends to come in sudden bursts.
The cough is usually worse at night. Many parents report that their child goes to bed with what seems like a mild cold, then wakes up a few hours later with a frightening barking cough. Crying and agitation can make the cough worse, because both increase airflow through the already narrowed passage.
Stridor: The Breathing Sound Between Coughs
Beyond the cough itself, many children with croup develop stridor, a high-pitched, squeaky or whistling sound when they breathe in. It happens because the swollen airway narrows enough that air vibrates as it passes through, similar to the sound of air squeezed through a tight opening. In young children, whose airways are already small, even a little swelling can produce this noise.
Stridor that only shows up when your child is upset or crying is a sign of mild to moderate croup. Stridor that you can hear while your child is calm and resting signals a more significant narrowing and a more serious episode.
Cold Symptoms That Come First
Croup almost always begins with a few days of typical cold symptoms: a runny nose, mild sore throat, and low-grade fever. These early signs look no different from any other upper respiratory infection. The barking cough and stridor then develop as the swelling moves deeper into the airway, usually one to three days after the cold symptoms start. This gradual onset is actually one of the features that distinguishes croup from more dangerous conditions like epiglottitis, which comes on suddenly with high fever and drooling.
Hoarseness and Voice Changes
Because the swelling centers on the voice box, children with croup often sound hoarse or raspy when they talk or cry. In babies who aren’t yet talking, you might notice that their cry sounds different from usual, weaker or rougher. This hoarseness tends to follow the same pattern as the cough, worsening at night and improving somewhat during the day.
Signs of Breathing Difficulty
In moderate to severe croup, the effort required to pull air through the swollen airway becomes visible. Look for retractions: the skin pulling inward around your child’s ribs, below the ribcage, or at the notch just above the breastbone with each breath. This happens because the chest muscles are working harder than normal to move air past the obstruction.
Other signs of respiratory distress include rapid breathing, flaring nostrils, and your child leaning forward or using their belly muscles to breathe. A child who seems unusually anxious, restless, or agitated may be struggling to get enough air, even if the stridor doesn’t sound dramatically loud.
Why Symptoms Peak at Night
Parents are often puzzled by how much worse croup gets after dark. Several factors contribute. The body’s natural production of cortisol, which helps control inflammation, drops to its lowest levels in the late evening and early morning hours. Lying flat also allows mucus to pool in the airway. Cool, dry air in a bedroom can further irritate already inflamed tissues. The combination means the worst episodes tend to hit between about 10 p.m. and 4 a.m., often for two or three nights in a row before gradually improving.
Mild, Moderate, and Severe Croup
Not every case of croup looks the same. Clinicians assess severity based on five key features: the level of consciousness, skin color changes (especially bluish tints around the lips or fingertips), stridor, how well air is moving in and out of the lungs, and the degree of chest retractions. Most children fall into the mild category, but understanding the spectrum helps you gauge what you’re seeing at home.
Mild croup means an occasional barking cough, no stridor at rest, and no visible retractions. Your child is alert, active between coughing fits, and breathing comfortably when calm.
Moderate croup involves stridor that you can hear even when your child is resting, along with visible retractions around the ribs and breastbone. The child may be restless or have trouble settling.
Severe croup includes loud stridor at rest, marked retractions, significantly reduced air movement, and sometimes a bluish or grayish tint to the skin around the mouth and fingernails. A child who becomes unusually drowsy, confused, or limp is showing signs of oxygen deprivation and needs emergency care immediately.
How Long Symptoms Last
The barking cough and stridor typically peak on the second or third night of illness, then gradually ease. Most children are noticeably better within three to five days, though a residual ordinary cough can linger for another week or so. If symptoms are getting worse after the third day rather than better, or if a fever spikes higher than it was initially, the infection may have progressed or a secondary bacterial infection may be developing.
Why Young Children Are Hit Hardest
Croup most commonly affects children between 6 and 36 months, though it can occur up to about age 5. The reason is purely anatomical. A toddler’s airway is already narrow, so even a small amount of swelling dramatically reduces the space available for air to flow through. An adult with the same virus might just get a hoarse voice and sore throat. In a small child, that same level of inflammation can cut the airway opening enough to produce the barking cough, stridor, and breathing difficulty that define croup.
How Croup Differs From Epiglottitis
One condition parents sometimes confuse with croup is epiglottitis, an infection of the flap of tissue at the base of the tongue. The two look quite different in practice. Croup comes on gradually over a day or two, features the classic barking cough, and hits children typically between 6 and 36 months. Epiglottitis strikes suddenly, often within hours, and tends to affect slightly older children (ages 2 to 8) and adults. A child with epiglottitis usually has a very high fever, drools because swallowing is painful, and prefers to sit upright and lean forward. The barking cough that defines croup is uncommon in epiglottitis. Thanks to routine vaccination, epiglottitis has become rare, but recognizing the differences matters because epiglottitis is a medical emergency that progresses quickly.