Is Croup Contagious? How to Know and How Long It Lasts (2024)

Croup is a contagious upper respiratory tract infection that can cause airway swelling and a hoarse, barking-like cough. Croup is most common in children aged between 3 months and 5 years. However, anyone can become infected.

Croup leads to swelling around the vocal cords and windpipe. Typically, children recover from croup on their own in three days to a week.

Is Croup Contagious? How to Know and How Long It Lasts (1)

How Long Is Croup Contagious?

Croup is contagious for the first three days after symptoms start—or until the infected person has been fever-free for 24 hours.

In general, after three days or an absence of fever, normal activities can be resumed. However, every child is different. Monitor symptoms and consult with your pediatrician or primary care provider when unsure. Some symptoms, like coughing, can persist, making it more challenging to return to all normal activities.

Fever in Children with Croup

While most children develop a fever with croup, some children never do. Younger children experience a fever at lower temperatures than adults. Fever is considered to be a temperature of:

  • 100.4 F (38 C) or higher in children under 3 months old if measured rectally or on the forehead
  • 99 F (37.2 C) or higher in children under 3 months old if measured in the armpit
  • 102 F (38.9 C) or higher in children between 3 months and 3 years old if measured rectally, on the forehead, or in the ear
  • 101 F (38.3 C) or higher in children between 3 months and 3 years old if measured in the armpit
  • 104 F (40 C)or higher in children of any age

Transmission

A parainfluenza virus causes the majority of croup cases, typically in the fall and early winter.

Most children get croup from breathing in respiratory droplets spread by sneezing, coughing, wheezing, or crying.

Importantly, having a croup infection in your household once doesn’t necessarily mean it won’t happen again. Children can get croup more than once.

Can Adults Get Croup from Children?

Croup can be passed among children and from a child to an adult. However, adults are much less likely to develop symptoms because they have larger airways—swelling doesn't affect them as much.

Adults often get croup from being in close contact with children who are contagious with the croup infection. In rare cases, croup is linked to allergies, bacteria, or acid reflux from the stomach.

Symptoms

Symptoms of croup include:

  • Cold symptoms, including runny nose and fever
  • Upper airway inflammation and swelling in the first 12–48 hours
  • Cough that sounds like seal barking (raspy and hoarse)
  • Increased breathing rate
  • High-pitched squeaky or crowing noise when breathing (stridor) in more moderate to severe cases

Croup typically gets worse before it improves: The illness begins with cold-like symptoms and progresses to the barking-cough characteristic of croup and breathing difficulties.

It is important to look out for stridor, a high-pitched breathing sound caused by abnormal airflow—it's a sign the croup is getting worse. Experts say symptoms can worsen during nighttime and when a child is upset and crying. If stridor occurs when a child is at rest (that is, when not crying or coughing), it is a sign of an emergency.

In the most serious cases (which are rare), experts say signs of croup worsening to emergency status include a pale or bluish color around the mouth due to a lack of oxygen. Less than 5% of children with croup require hospitalization. Even in these cases, croup hospitalization is typically no more than a few hours to two days.

When to Seek Immediate Medical Care

Complications with croup are uncommon. Experts recommend calling 911 or going directly to the nearest emergency room if the child with a croup infection experiences the following symptoms:

  • Stridor at rest
  • Pale, bluish, or grayish skin around mouth and face
  • Skin around mouth or fingernails starts turning blue when coughing
  • Not being able to catch their breath
  • Drooling or cannot swallow
  • Excessive tiredness or difficulty waking up
  • Signs of dehydration (no tears while crying, peeing less, sunken eyes)

How to Prevent Spread

To prevent the spread of croup, children with symptoms should not go to school or daycare for the first three days after the onset of symptoms—or until their fever resolves.

Other methods of preventing the spread of croup to others include:

  • Practice proper hand hygiene (frequent and thorough hand washing and drying).
  • Teach children how to cough into their elbows instead of their hands.
  • Stay up-to-date on the latest vaccinations that can help prevent some respiratory illnesses.
  • Follow your healthcare provider’s treatment protocol, which may include medications.

Summary


Croup is an infection typically seen in children between the ages of 3 months and 5 years. The virus can spread among children and between children and adults. However, older children and adults typically don't experience any symptoms.

The croup infection is contagious until three days after symptoms start or, if fever is present, until the fever resolves. While a person with croup is contagious, the virus in mucus or respiratory droplets spreads through sneezing, coughing, crying, and wheezing.

10 Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

  1. Cedars-Sinai. Croup in children.

  2. Nationwide Children’s Hospital. Croup.

  3. MedlinePlus. Croup.

  4. Texas Children's Hospital. Common illnesses seen after natural disasters: Croup.

  5. American Academy of Family Physicians’ Family Doctor. Croup.

  6. Woods, Charles. Patient education: Croup in infants and children (beyond the basics).

  7. Nemours Kids Health. Croup.

  8. Smith DK, McDermott AJ, Sullivan JF. Croup: diagnosis and management.Am Fam Physician. 2018;97(9):575-580.

  9. Johns Hopkins Medicine. Croup.

  10. Seattle Children's Hospital Research Foundation. Croup.

Is Croup Contagious? How to Know and How Long It Lasts (2)

By Michelle Pugle
Michelle Pugle, MA is a freelance writer and reporter focusing on mental health and chronic conditions. As seen in Verywell, Healthline, Psych Central, Everyday Health, and Health.com, among others.

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