What is a normal axillary (armpit) temperature?

Normal Axillary Temperature Range

Normal axillary temperature in healthy adults ranges from approximately 36.0-36.9°C (96.8-98.4°F), with a mean of 36.47°C (97.65°F), though this is consistently 0.5-1.9°C lower than core body temperature and should not be used as a reliable substitute for oral or rectal measurements in clinical decision-making. 1, 2

Key Temperature Values

• Mean axillary temperature in modern adults: 36.47 ± 0.28°C (36.48°C in males, 36.35°C in females) 1
• Expected difference from core temperature: Axillary readings are consistently 1.5-1.9°C below tympanic/core temperatures 2
• Expected difference from oral temperature: Axillary readings average 1.0-1.17°C lower than oral measurements 3, 4
• Expected difference from rectal temperature: Axillary readings average 1.15-1.81°C lower than rectal measurements 5, 4

Critical Clinical Context

Axillary temperature is fundamentally unreliable for clinical decision-making and should never be used to rule out fever or guide treatment decisions. 2, 6

Why Axillary Measurements Are Problematic:

• Poor sensitivity: Only 46% sensitive for detecting fever, with wide limits of agreement (0.32-1.98°C variation from rectal temperature) 5, 4
• High variability: Up to 1°C inconsistency between measurements, with bilateral axillary readings differing by as much as 3.4°F 2, 3
• Temperature-dependent error: The discrepancy increases with fever—at 39°C fever, axillary readings can be over 1°C lower than actual core temperature 7
• External factors: Easily disturbed by ambient temperature, local blood flow, and incorrect probe placement 2

When Axillary Temperature Is Acceptable

Axillary measurement is only appropriate for screening purposes or monitoring temperature trends in preterm neonates (<34 weeks gestation) during NICU care, where it is used to detect hypothermia (<36.0°C) or hyperthermia (>38.0°C). 2, 6

Critical Exception - Newborn Fever Diagnosis:

Never use axillary temperature to diagnose or rule out fever in newborns presenting with concern for infection—rectal temperature is the only acceptable method because missing serious bacterial infection (which occurs in 8-13% of febrile infants) can be fatal. 6

Preferred Temperature Measurement Methods (In Order)

1. Central monitoring (pulmonary artery catheter, bladder catheter, esophageal probe): Gold standard for core temperature 2
2. Rectal temperature: Most accurate peripheral method, required for fever diagnosis in newborns 2, 6
3. Oral temperature: Acceptable for cooperative adults when central monitoring unavailable 2
4. Axillary temperature: Only for screening or trend monitoring in specific populations (preterm infants); never for diagnostic decisions 2, 6

Factors Affecting Axillary Temperature

• Age: Body temperature decreases with age; no subjects ≥50 years had axillary temperature ≥37°C in recent studies 1
• Time of day: Afternoon measurements run approximately 0.5°C higher 1
• Blood pressure and pulse rate: Both correlate with measured axillary temperature 1
• Measurement technique: Requires proper probe placement over axillary artery with arm adducted for 3-5 minutes 2

Common Pitfalls to Avoid

• Never add a fixed correction factor (like 1°F) to axillary readings to estimate core temperature—the difference is not constant and increases with fever 5, 7
• Never rely on single-side axillary measurement—bilateral readings can differ by up to 3.4°F; averaging both sides is more accurate 3
• Never use axillary temperature in emergency settings where accurate fever detection is critical for management decisions 4
• Never delay sepsis workup in neonates based on normal axillary temperature—always confirm with rectal measurement 6