Normal Temperature Range for Infants
The normal body temperature range for infants is 36.5°C to 37.5°C (97.7°F to 99.5°F) when measured rectally, which is the gold standard measurement method for this age group. 1, 2
Measurement Method Matters
- Rectal temperature is the most accurate and recommended method for infants and young children under 3 years of age 2, 3
- Axillary (armpit) temperatures are less reliable, typically measuring 0.7°C lower than rectal temperatures with a wide range of variation (up to 3°C difference), making them too insensitive for accurate detection of temperature abnormalities 3
- The sensitivity of axillary temperature for detecting fever is only 73% compared to rectal measurement 3
Age-Specific Temperature Variations
Temperature norms vary slightly by infant age:
- Birth to 30 days: Normal up to 38.0°C rectally 4
- 31 to 60 days: Normal up to 38.1°C rectally 4
- 61 to 91 days: Normal up to 38.2°C rectally 4
The mean rectal temperature across healthy infants under 3 months is 37.5°C ± 0.3°C 4
Clinical Temperature Thresholds
Fever is defined as:
- ≥38.0°C (100.4°F) rectal temperature in infants under 3 years 2, 5
- This threshold represents the 95th percentile for normal infant temperatures 4
Hypothermia is defined as:
- <36.5°C (97.7°F) core temperature, requiring immediate intervention 2, 6
- Even modest hypothermia carries significant risk, with mortality increasing by at least 28% for each 1°C drop below 36.5°C 1, 6
Hyperthermia (to be avoided):
38.0°C when caused by environmental factors or overheating 1, 7
- Associated with increased mortality and adverse neurologic outcomes 7
Important Clinical Context
Environmental and physiologic factors affecting temperature:
- Room temperature should be maintained at 23-25°C (73-77°F) for infants 1, 2, 6
- Temperature varies with season, being higher in summer (up to 38.3°C normal) than winter 4
- Hypothermia risk is highest in the first 8 hours after birth, occurring in 28% of term infants even in adequate thermal environments 8
- Hyperthermia risk increases after 8 hours of life, particularly in larger infants during skin-to-skin care 8
Critical Pitfalls to Avoid
- Never dismiss mild temperature abnormalities in infants - even small deviations below 36.5°C significantly increase mortality risk 2, 6
- Do not rely on axillary temperatures alone when clinical concern exists - confirm with rectal measurement 2, 3
- Avoid using thermal mattresses or heating pads for warming, as these increase burn and hyperthermia risk 6, 7
- Using the widely accepted 38.0°C fever threshold means approximately 6.5% of healthy infants would be classified as febrile, which is clinically acceptable 4