Body Temperature
Definition
Core body temperature, typically measured orally, aurally (ear), temporally (forehead), or rectally.
Why It Matters
Body temperature is a fundamental vital sign: - Fever detection - Indicates infection, inflammation - Hypothermia - Dangerously low temperature - Thermoregulation - Body's ability to maintain temperature - Illness monitoring - Tracking fever progression - Post-operative care - Monitoring recovery
How It's Measured
Various measurement sites with different accuracy:
| Method | Normal Range | Notes |
|---|---|---|
| Oral | 36.4-37.4°C (97.5-99.3°F) | Most common |
| Tympanic (ear) | 35.8-38.0°C (96.4-100.4°F) | Quick, variable |
| Temporal (forehead) | 35.8-38.0°C (96.4-100.4°F) | Non-contact available |
| Axillary (armpit) | 35.2-36.9°C (95.4-98.4°F) | Less accurate |
| Rectal | 36.8-38.0°C (98.2-100.4°F) | Most accurate |
HealthKit data: Usually from manual entry or connected thermometers.
Reference Values
- Normal: ~37°C (98.6°F), but varies by individual
- Fever: Generally ≥38°C (100.4°F) orally
- Hypothermia: <35°C (95°F)
Important: Normal body temperature varies by: - Time of day (lowest in morning, highest in evening) - Activity level - Menstrual cycle phase - Individual baseline
Confounders & Limitations
- Measurement site - Different sites give different values
- Recent food/drink - Hot/cold items affect oral readings
- Activity - Exercise elevates temperature
- Environment - Cold exposure lowers readings
- Medications - Some affect thermoregulation
- Device accuracy - Consumer thermometers vary
Use Cases
- Illness detection - Fever screening
- Symptom tracking - Monitoring infection course
- COVID/illness screening - Temperature checks
- General wellness - Baseline awareness
When to Seek Care
- Fever >39.4°C (103°F) in adults
- Fever lasting more than 3 days
- Fever with severe symptoms
- Any hypothermia (<35°C/95°F)
- Fever in infants (follow pediatric guidelines)