What are the key clinical features to differentiate mild, moderate, and severe croup in children?

Guideline-aligned answer with reasoning, red flags and references. Clinically reviewed by Dr Kola Tytler MBBS CertHE MBA MRCGP.

Posted: 16 August 2025Updated: 16 August 2025 Guideline-Aligned (High Confidence) Clinically Reviewed
Dr Kola Tytler MBBS CertHE MBA MRCGPClinical Lead • iatroX

UK guidelines primarily differentiate the severity of croup based on clinical features that indicate the need for hospital admission or emergency care .

  • Features indicating Moderate or Severe Croup (requiring hospital admission or emergency care):
    • Respiratory Signs: Continuous stridor , marked chest recession (skin pulling in between the ribs or over the windpipe, or the belly sinking in with every breath) , flaring nostrils , grunting , a respiratory rate over 60 breaths/minute (which may prompt admission even in mild illness) , or a respiratory rate over 70 breaths/minute (indicating severe respiratory distress) . There may also be general trouble breathing or poor respiratory effort ,.
    • Consciousness and Behavioural Changes: Restlessness or agitation, especially if the child is upset while struggling to breathe and cannot be calmed quickly . Signs of unusual sleepiness, unresponsiveness , listlessness, or exhaustion are also critical indicators.
    • Oxygenation and Circulation: Very pale, grey, or blue skin (including blue lips) for more than a few seconds , central cyanosis , or persistent oxygen saturation below 90% (for children aged 6 weeks and over) or below 92% (for babies under 6 weeks or children with underlying health conditions) .
    • Feeding and Swallowing: Inadequate oral fluid intake (50% to 75% of usual volume, or no wet nappy for 12 hours) , inability to talk, drooling, trouble swallowing, or wanting to sit instead of lie down .
    • Other Critical Signs: Observed or reported apnoea , a high fever, or a 'toxic' appearance .
  • Features indicating Mild Croup:
    • Mild croup is generally characterised by the absence of the severe features listed above . Symptoms typically resolve within 48 hours . Management for mild croup usually involves home care, including the use of paracetamol or ibuprofen for fever or pain, and encouraging regular fluid intake . However, even children with mild illness may require hospital admission if there are factors that lower the threshold for admission, such as age under three months, chronic lung disease, or inadequate fluid intake .

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What are the key clinical features to differentiate mild, moderate, an