Body temperature is a vital physiological parameter and a key indicator of health status. In nursing practice, accurate measurement and interpretation of body temperature are essential for early detection of illness, monitoring disease progression, and evaluating the effectiveness of treatment. Although 37°C (98.6°F) is widely accepted as the “normal” body temperature, it is important to recognise that normal temperature varies among individuals and under different conditions.
Normal Body Temperature for Adults
Normal Body Temperature Values
In healthy adults, average normal body temperature differs depending on the site of measurement:
- Oral: 37.0°C (98.6°F)
- Rectal: 37.6°C (99.6°F)
- Axillary: 36.4°C (97.6°F)
Overall, normal body temperature for a healthy adult generally ranges between 36.5°C to 37.2°C (97.8°F to 99.0°F).
Physiological Variations in Body Temperature
Normal body temperature is not constant and may vary due to several factors, including:
- Gender
- Age
- Recent physical activity
- Food and fluid intake
- Time of day (typically lower in the early morning and higher in the late afternoon or evening)
- Hormonal changes, particularly during the menstrual cycle in women
These variations should be considered when assessing a patient’s temperature to avoid misinterpretation.
Methods of Measuring Body Temperature
Body temperature can be measured using various routes, each with its own clinical relevance:
1. Oral Method
- Measured using glass or digital thermometers
- Commonly used in cooperative adults
- Affected by recent eating, drinking, smoking, or mouth breathing
2. Rectal Method
- Considered the most accurate reflection of core body temperature
- Typically 0.5–0.7°F (0.3–0.4°C) higher than oral temperature
- Used when precise measurement is required
- Contraindicated in certain conditions (e.g. rectal surgery, bleeding disorders)
3. Axillary Method
- Measured under the arm
- Usually 0.3–0.4°F (0.2–0.3°C) lower than oral readings
- Less accurate but useful when other routes are unsuitable
4. Tympanic (Ear) Method
- Measures infrared heat from the eardrum
- Reflects core temperature
- Quick and convenient, but accuracy depends on correct placement
5. Temporal Artery (Forehead/Skin) Method
- Measures temperature of the skin over the temporal artery
- Non-invasive and rapid
- Useful in mass screening and paediatric care
Abnormal Body Temperature
Body temperature may become abnormal due to either fever (pyrexia) or hypothermia.
Fever
- Defined as a rise in body temperature of approximately 1°F (0.6°C) or more above normal
- Commonly indicates infection or inflammation
- According to clinical guidelines, fever often reflects the body’s immune response to illness
Hypothermia
- Defined as a body temperature below 35°C (95°F)
- May occur due to exposure to cold, shock, metabolic disorders, or impaired thermoregulation
- Requires urgent medical attention
Factors Influencing Heat Production in the Body
Several physiological and environmental factors affect heat production and body temperature regulation:
- Metabolism: Heat is produced through oxidation of food during metabolic processes
- Muscle activity: Exercise and shivering significantly increase heat production
- Emotional state: Strong emotions such as excitement, anxiety, and nervousness raise temperature
- Environmental temperature: Changes in atmospheric temperature influence heat loss and gain
- Disease conditions: Infections, especially bacterial invasion, commonly elevate body temperature
- Sympathetic nervous system stimulation: Hormones such as epinephrine and norepinephrine increase metabolic rate and heat production
Nursing Considerations
- Always use the same measurement site when monitoring temperature trends
- Document the route of measurement along with the temperature value
- Assess temperature in conjunction with other vital signs
- Be aware of factors that may falsely elevate or lower readings
- Report abnormal findings promptly and initiate appropriate nursing interventions
Normal body temperature in adults is a dynamic parameter influenced by physiological, environmental, and pathological factors. Understanding normal ranges, variations, and methods of measurement is essential for accurate assessment and safe nursing practice.
For nurses, recognising subtle changes in temperature can provide early warning signs of infection, systemic illness, or environmental exposure. Accurate measurement, interpretation, and documentation of body temperature remain fundamental components of high-quality patient care.