What is a 'Normal' Temperature?
For decades, 37°C (98.6°F) has been cited as the standard for normal human body temperature. However, this number, derived from 19th-century research, is now viewed as an oversimplification. Modern research shows that a healthy adult's temperature can vary, with an overall average potentially closer to 36.6°C (97.9°F). Factors such as the time of day, with temperatures typically at their lowest in the early morning, can cause fluctuations. For an adult, a reading of 35.5°C is generally considered low and should be interpreted carefully in context with other symptoms and factors.
Understanding Temperature Measurement Sites
The reading on your thermometer is also highly dependent on where you take the measurement. Different parts of the body yield different average temperatures. The most accurate readings reflect the body's core temperature, with less accurate readings found on the skin's surface.
Comparison of Temperature Measurement Methods
| Method | Approximate Normal Adult Range | Comparison to Oral | Notes |
|---|---|---|---|
| Rectal | 36.7°C to 37.5°C | Higher (by approx. 0.3-0.6°C) | Considered the most accurate for core temperature. |
| Oral | 36.1°C to 37.2°C | Baseline | Can be affected by eating, drinking, or smoking. |
| Tympanic (Ear) | 35.5°C to 37.5°C | Higher (by approx. 0.3-0.6°C) | Can be less accurate, especially if not placed correctly. |
| Axillary (Armpit) | 35.5°C to 37.0°C | Lower (by approx. 0.5°C) | Less reliable and less accurate for core temperature. |
| Temporal Artery (Forehead) | Similar to Oral | Varies | Accuracy can be affected by sweat or cold exposure. |
As this table shows, a 35.5°C reading might be within a normal range for an armpit or ear measurement, but would be low if taken orally or rectally. It is crucial to use a consistent method to track your personal baseline temperature.
Possible Reasons for a Low Temperature
If you have an oral or rectal temperature reading of 35.5°C, it's considered low and could be caused by several factors. These range from benign and manageable issues to more serious health concerns that require medical attention.
Environmental Factors
- Cold Exposure: The most common cause is exposure to a cold environment, which can lead to hypothermia if the body loses heat faster than it can produce it.
- Wet Clothing: Being in wet clothing in cold or windy conditions can dramatically accelerate heat loss.
- Sedentary Lifestyle: A lack of physical activity, especially in older adults, can reduce metabolism and heat production.
Medical Conditions
- Hypothyroidism: An underactive thyroid gland slows down metabolism, which directly impacts the body's ability to generate heat.
- Sepsis: In some cases, a severe infection can lead to an inflammatory response that causes body temperature to drop significantly. This is a medical emergency.
- Age: Older adults naturally have a lower core body temperature due to changes in metabolism and less subcutaneous fat.
- Nutritional Deficiencies: Poor nutrition, malnutrition, or anorexia nervosa can impair the body's ability to maintain a stable temperature.
- Nervous System Disorders: Conditions affecting the hypothalamus, the brain's thermostat, can disrupt temperature regulation.
Medications and Other Factors
- Certain Medications: Some drugs, including certain antidepressants, sedatives, beta-blockers, and antipsychotics, can interfere with the body's temperature regulation.
- Alcohol or Drug Use: These substances can affect judgment and increase heat loss by dilating blood vessels, making the person more susceptible to cold.
What to Do If Your Temperature is Low
Taking your temperature once isn't always enough. A slightly low reading might not be concerning if you feel fine. However, if your reading is consistently low or you have other symptoms, you should take action. First, recheck the temperature to ensure accuracy, considering the time of day and measurement site. If the low temperature is accompanied by concerning symptoms, do not ignore it.
- If you suspect hypothermia: If the low temperature follows cold exposure and is accompanied by symptoms like confusion, slurred speech, or uncontrollable shivering, seek immediate medical attention by calling emergency services.
- Warm up gradually: Get to a warm, dry place. Remove any wet clothing and cover yourself with blankets. Sip warm, non-alcoholic fluids like broth or tea. Do not use direct heat sources like a heating pad or hot bath, as this can cause rapid rewarming, which can be dangerous.
- Address underlying causes: If a medical condition is the cause, treating it can help normalize body temperature. Consult a healthcare provider to explore potential issues like thyroid dysfunction.
When to Seek Medical Help
While a slightly low reading can sometimes be harmless, certain signs indicate a need for professional medical evaluation. According to the CDC, if you or someone you know has a body temperature below 35°C (95°F), it constitutes a medical emergency.
Signs and symptoms that warrant a call to emergency services or a visit to the doctor include:
- Persistent shivering or, conversely, shivering that has stopped after a period of being cold.
- Confusion, memory loss, or poor judgment, which can occur during moderate hypothermia.
- Slurred speech, shallow breathing, or a weak pulse.
- Loss of consciousness.
- In infants, bright red, cold skin, or very low energy.
Conclusion
While a 35.5°C temperature may not be an immediate cause for alarm, particularly if taken from the armpit, it is not a typically normal oral or rectal reading for an adult. It should be taken seriously as a potential indicator of an underlying issue, ranging from aging and environmental factors to more critical conditions like severe infection or thyroid problems. Understanding your personal baseline and knowing when to seek professional help is essential for monitoring your health effectively. Always ensure you are measuring your temperature correctly and consistently for the most accurate results. For comprehensive information on how to properly measure your temperature, see the guide provided by the National Jewish Health.
