Croup – Symptoms, causes and other associated risk factors


Croup is a childhood condition which affects the voice box (larynx), the airways to the lungs (the bronchi) and the windpipe (trachea). Children who suffer from this condition have a distinctive barking cough and they will make a harsh sound, when they breathe in. This harsh sound is known as stridor. Also they can have a hoarse voice and it is very difficult for them to breathe because their airways are blocked. [1] This condition can be usually diagnosed by your doctor and it can be treated at home. If you have noticed that your child has severe symptoms and if he or she finds difficult to breathe, then you should take them to the nearest emergency hospital. Most often, croup is caused by a virus. There are several viruses which can lead to croup but in the most cases it is caused by parainfluenza virus.

Symptoms of croup

A child can get croup at any time of the year. It is more likely to happen during early winter or late autumn. This is happening because there are more viruses such as flu and cold, around these times of the year. Here are typical symptoms of croup [1]:

  • A harsh grating sound when breathing in, called stridor
  • Difficulty breathing
  • A hoarse or croaky voice
  • A bark – like cough

Stridor is most often noticeable when the child coughs or cries. But when some children have more severe cases of croup, the stridor can happen when child is sleeping or resting. Symptoms tend to be worse at night. Also there are some children who have cold – like symptoms for a few days before they develop the symptoms of croup. These cold – like symptoms can include:

  • High temperature (fever)
  • Cough
  • Runny nose
  • Sore throat

In the most cases croup can last only for a few days, but occasionally they can last up to 2 weeks.


Causes of croup

This condition usually develops as the result of a viral infection. The infection may affect the tubes in the lungs (bronchi), trachea (windpipe) to become blocked and the larynx (voice box) to become swollen. There are some cases when this condition is called laryngo – trachea – bronchitis.

Parainfluenza virus: This is the most common cause of croup [2]. There are four strains of the virus that are responsible for most croup cases and they are:

  • Parainfluenza I
  • Parainfluzenza II
  • Parainfluenza III
  • Parainfluenza IV

Parainfluenza I is responsible for the most cases of croup. The virus can be transmitted through contaminated objects and surfaces and close contact with infected people. As it is the case with many airborne viruses, this virus is often spread by breathing in droplets from sneezes or infected coughs.

Other viruses: There are many other viruses that can lead to croup such as:

  • RSV – the respiratory syncytial virus, which can cause severe breathing problems and pneumonia in babies [3]
  • Enteroviruses
  • The rhinovirus (common cold virus)
  • The measles virus, in children who have not been immunized against measles [4]
  • Influenza A and B (flu viruses) [5]

Other causes: Also there are less common causes for croup such as

  • Acid leaking back out of the stomach and into the throat (acid reflux) [6]
  • Inhalation or irritants, such as chemicals
  • An allergic reaction to substances such as pollen or dust mites
  • Epiglottitis, which is an inflammation of the epiglottis. They are the flap base of the tongue that keeps food from going into the windpipe [7]
  • Inhaling a small object such as a peanut or pen cap (inhaled foreign body)

Complications: Complications which can develop as a result of croup are rare.

  • Airway obstruction: If the obstructed airway is not treated promptly, then it can lead to:
  • Respiratory arrest (where breathing stops but the heart continues beating)
  • Severe breathing difficulty (respiratory distress) [8]

Secondary infection: This type of infection can sometimes develop following the initial infection which caused croup. The secondary infection can cause:

  • Bacterial tracheitis, which is a serious and potentially life – threatening infection that can occur after a viral respiratory infection [9]
  • Pneumonia which is a chest infection which causes swelling of the tissue in one or both lungs resulting in croup [2,10]


[1] Bjornson CL, Johnson DW. Croup in children. CMAJ. 2013;185(15):1317–23.

[2] Fathima S, Simmonds K, Invik J, et al. Use of laboratory and administrative data to understand the potential impact of human parainfluenza virus 4 on cases of bronchiolitis, croup, and pneumonia in Alberta, Canada. BMC Infectious Diseases. 2016;16.

[3] Griffiths C, Drews SJ, Marchant DJ. Respiratory syncytial virus: Infection, detection, and new options for prevention and treatment. Clinical Microbiology Reviews. doi:10.1128/CMR.00010-16

[4] Perry RT, Halsey NA. The clinical significance of measles: A review. The Journal of Infectious Diseases. 2004;189:S4-S16.

[5] Poland JD, Welton ER, Chin TDY. Influenza Virus B as cause of acute croup syndrome. The American Journal of Diseases of Children. 1964;107(1):54-7. doi:10.1001/archpedi.1964.02080060056008

[6] Ślączka K, Dziekiewicz MA, Jabłońska-Jesionowska M, Zawadzka-Glos L. Gastroesophageal reflux disease in children with recurrent croup. New Medicine. 2016;20(4):114-7.

[7] Davis HW, Gartner C, Galvis AG, et al. Acute upper airway obstruction: Croup and epiglottitis. Pediatric Clinics of North America. 1981;28(4):859-80.

[8] Lin SC, Lin HW, Chiang BL. Association of croup with asthma in children: A cohort study. Medicine. 2017;96(35):e7667. doi: 10.1097/MD.0000000000007667

[9] Kuo CY, Parikh SR. Bacterial tracheitis. Pediatrics in Review. 2014;35(11):497-9. doi:

[10] Horvath G, Acs K. Essential oils in the treatment of respiratory tract diseases highlighting their role in bacterial infections and their anti‐inflammatory action: a review. Flavour and Fragrance Journal. 2015;30(5):331-41.


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