Normal Human Body Temperature: Range, Variation, and Clinical Meaning

The classic "98.6°F (37°C)" is a population average, not a fixed standard for any individual.

Normal Range

• Oral: 97.0–99.5°F (36.1–37.5°C)
• Rectal/Tympanic: ~0.5–1°F higher.
• Axillary: ~0.5–1°F lower.

Sources of Variation

• Circadian rhythm: Lowest ~4–6 AM; peak ~4–6 PM (amplitude ~0.5–1°C).
• Age: Older adults average lower; infants higher.
• Activity, meals, ovulation (↑0.5°F post-ovulation), hormones, ambient temperature.
• Measurement site and device accuracy.

Fever Definitions

• Low-grade: 99.5–100.3°F (37.5–37.9°C) oral.
• Fever: ≥100.4°F (38.0°C) oral/rectal.
• Hyperpyrexia: ≥106°F (41.1°C)—medical emergency.

Clinical Pearl

Know your baseline. A temperature of 99.8°F may be significant for someone whose typical is 97.2°F. Trends matter more than single readings.