What is Fever?

Fever remains the most common concern prompting parents to present their child to the emergency department. Fever has traditionally been defined as a rectal temperature over 100.4 F or 38 C. Temperatures measured at other body sites are usually lower. The threshold for defining a fever does vary significantly among different individuals, since body temperatures can vary by as much as 1 F. Low-grade fevers are usually considered less than 102.2 F (39 C).

Fever itself is not life-threatening unless it is extremely and persistently high, such as greater than 107 F (41.6 C) when measured rectally. Risk factors for worrisome fevers include age under 2 years (infants and toddlers) or recurrent fevers lasting more than one week. Fever may indicate the presence of a serious illness, but usually a fever is caused by a common infection. However, many conditions other than infections may cause a fever. 

Call your doctor if:
Call a child's doctor if any of the following are present with fever.

  • The child is younger than 6 months of age (regardless of prematurity).
  • One is unable to control the fever.
  • One suspects a child may become dehydrated from vomiting, diarrhea, or not drinking (for example, the child has sunken eyes, dry diapers, tented skin, cannot be roused, etc.).
  • The child has been to a doctor but is now getting worse or new symptoms or signs have developed.

Tips for helping your child with a fever:

  • When giving fever medication follow the dosage and frequency instructions printed on the label. Please consult your pharmacist or doctor before giving a dose.
  • Do not use aspirin to treat fever in children, especially for a fever with chickenpox or other viral infection. Aspirin has been linked to liver failure in some children.
  • A sponge bath in warm water will help reduce a fever.
  • Children should not be overdressed indoors, even in winter.
  • To prevent dehydration, give the child clear fluids


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Enarson MC, Ali S, Vandermeer B, Wright RB, Klassen TP, Spiers JA. Beliefs and expectations of Canadian parents who bring febrile children for medical care. Pediatrics. 2012 Oct 1;130(4):e905-12.

Pierce, C.A., and B. Voss. "Efficacy and Safety of Ibuprofen and Acetaminophen in Children and Adults: A Meta-analysis and Qualitative Review." Ann Pharmacother44 (2010): 489-506.

Sullivan JE, Farrar HC. Fever and antipyretic use in children. Pediatrics. 2011 Mar 1;127(3):580-7.

Tolan Jr., R.W. "Fever of Unknown Origin: A Diagnostic Approach to This Vexing Problem." Clin Pediatr (Phila) 49 (2010): 207-213.