Normal Body Temperature in Children
The normal body temperature in children is approximately 36.5°C to 37.5°C (97.7°F to 99.5°F) when measured rectally, with fever defined as a rectal temperature ≥38.0°C (100.4°F). 1
Age-Specific Temperature Definitions
The definition of fever varies slightly by age in young infants, reflecting physiologic maturation:
- Birth to 30 days old: Fever is ≥38.0°C (100.4°F) 2
- 31 to 60 days old: Fever is ≥38.1°C (100.4°F) 2
- 61 to 91 days old: Fever is ≥38.2°C (100.4°F) 2
- 2 months to 2 years: Fever is ≥38.0°C (100.4°F) 1
Normal Temperature Ranges by Context
Neonatal and Preterm Infants
Normothermia in newborns is defined as a core body temperature between 36.5°C and 37.5°C (97.7°F to 99.5°F). 1
- Hypothermia is defined as <36.0°C (96.8°F) 1
- Moderate hypothermia is <36°C 1
- Hyperthermia is defined as >37.5°C (99.5°F) 1
Critical Temperature Thresholds for Clinical Decision-Making
For brain death evaluation in children, core body temperature must be ≥35°C (95°F) to ensure accurate neurologic assessment. 1 This emphasizes that hypothermia significantly affects physiologic function and clinical evaluation.
In heat-related illness, rectal temperature >40°C (104°F) indicates exertional heat stroke requiring immediate cooling. 1 Cooling should continue until rectal temperature reaches just under 39°C (approximately 102°F) 1.
Important Clinical Considerations
Measurement Site Matters
Rectal temperature is considered the gold standard for measuring core body temperature in children and is the preferred method for fever assessment in infants and young children. 1, 3 The mean rectal temperature in healthy infants less than 3 months old is 37.5°C ± 0.3°C 2.
Individual Variation
While 37.0°C (98.6°F) is historically cited as "normal," this is an oversimplification. Mean temperatures in healthy infants range from 35.2°C to 37.4°C (95.4°F to 99.3°F) across individuals 4. Temperature also varies by:
- Season: Higher in summer (up to 38.3°C) than winter (38.0°C) 2
- Time of day: Diurnal variation occurs 4
- Sex: Females tend to have slightly higher temperatures 4
Common Pitfalls to Avoid
Do not rely on home thermometer readings without verification, as accuracy varies significantly. 1 Parents should be instructed on proper measurement technique.
Recent antipyretic use (within 4 hours) may mask fever and underestimate the true temperature. 1 Always inquire about medication administration before temperature assessment.
Peripheral measurement sites (axillary, forehead) are not reliable for assessing core body temperature in children. 5 When fever detection is critical, use rectal measurement in young children or tympanic/temporal artery thermometry in older children (>2 years) 3.
A child with serious bacterial infection may appear well initially despite fever. 1, 6 Clinical appearance alone is insufficient; 58% of febrile infants with bacteremia or bacterial meningitis appeared clinically well 1.