A body temperature below the commonly cited 98.6°F (37°C) is usually normal. Healthy adults can range from 97°F to 99°F (36.1°C to 37.2°C) without anything being wrong. That said, a persistently low reading, especially below 97°F, can point to specific causes worth understanding.
Normal Temperature Is a Range, Not a Number
The 98.6°F figure dates back to a 19th-century study and has stuck around as a rough benchmark, but it oversimplifies how body temperature actually works. Your temperature shifts throughout the day, hitting its lowest point in the early morning and climbing as the day goes on. That means a reading of 97.2°F before breakfast is perfectly typical, even if it looks low on paper.
Beyond daily rhythms, your personal baseline matters. Some people simply run cooler than others. Age, activity level, and even the time since your last meal all influence the number on the thermometer. If you’ve always gotten readings in the low 97s and feel fine, that’s likely just your normal.
Your Thermometer Might Be the Problem
Before looking for medical explanations, consider how you’re taking your temperature. Different body sites give different readings, and there’s no reliable formula to convert between them. Armpit (axillary) readings tend to run lower than oral readings, which in turn run lower than rectal readings. A forehead scan can also skew low if your skin is cool or sweaty.
Rectal readings are the most accurate, though most adults use oral thermometers. If you’re getting surprisingly low numbers, try measuring again with the thermometer properly placed under your tongue, mouth closed, after avoiding cold drinks for at least 15 minutes. Comparing readings taken the same way, at the same time of day, gives you the most useful picture.
Low Thyroid Function
Your thyroid gland acts as a thermostat for your metabolism. It produces hormones that drive energy expenditure and heat generation throughout your body. When thyroid function drops, a condition called hypothyroidism, your metabolic rate slows and you produce less heat at rest.
The mechanism is specific: your body relies on converting one form of thyroid hormone (T4) into its active form (T3) to regulate temperature. Research published in the Journal of the Endocrine Society found that people with controlled hypothyroidism still had measurably lower skin temperatures than healthy controls, even when their condition was being treated with medication. This suggests that subtle impairments in hormone conversion can keep body temperature lower than expected. Common symptoms alongside low temperature include fatigue, weight gain, dry skin, and feeling cold when others don’t.
Iron Deficiency and Anemia
Iron plays a larger role in temperature regulation than most people realize. When you’re iron-deficient, your blood carries less oxygen from your lungs to your tissues. That reduced oxygen supply impairs two key warming mechanisms: the narrowing of blood vessels near your skin’s surface (which conserves heat) and the ability to rev up your metabolic rate (which generates heat).
The problem goes even deeper than oxygen delivery. Low iron reduces the activity of energy-producing enzymes inside your muscle cells, making it harder for muscles to generate warmth. Iron deficiency also disrupts signaling in the brain that triggers thyroid hormone release in response to cold, essentially blunting the very system your body uses to warm itself. If you’re running cold and also dealing with fatigue, pale skin, or shortness of breath during exertion, iron levels are worth checking.
Medications That Affect Temperature
Several common medications interfere with your body’s ability to regulate its internal temperature. The drugs most likely to cause issues include:
- Beta-blockers (used for blood pressure and heart conditions): these reduce blood flow to the skin’s surface, limiting your body’s ability to manage heat exchange.
- Antipsychotic medications: these can directly impair the brain’s temperature control center, as well as reduce sweating.
- Certain antidepressants: tricyclic antidepressants and some SSRIs affect sweating and thermoregulation.
- Antihistamines with sedating effects (like diphenhydramine): these have anticholinergic properties that interfere with thermoregulation.
- Anti-seizure medications: some, like topiramate, decrease sweating and alter heat balance.
If you started a new medication and noticed your temperature readings dropping, the drug could be a factor. This doesn’t necessarily mean you should stop taking it, but it’s useful context for understanding what your thermometer is telling you.
Age-Related Changes
Older adults tend to read lower on the thermometer, and the reasons are largely physical. With aging, the layer of insulating fat beneath the skin thins out, making it harder to retain body heat. The body’s temperature-control system also becomes less responsive, meaning it’s slower to ramp up heat production when needed.
This has a practical consequence beyond comfort. Because older adults run cooler at baseline, a temperature of 99°F that wouldn’t raise eyebrows in a younger person could actually represent a significant fever in someone over 65. Likewise, a serious infection might not produce a fever at all. If you’re older and consistently reading below 97°F, it helps to know your personal baseline so that meaningful changes don’t get dismissed.
Infection Without Fever
Most people associate infection with fever, but severe infections can actually drive body temperature down. In sepsis, the body’s overwhelming response to infection sometimes causes hypothermia rather than a temperature spike. This is more common in older adults, people with weakened immune systems, and those with a history of heavy alcohol use.
A dropping temperature during an acute illness is a red flag, not a reassuring sign. If you’re feeling very unwell with symptoms like confusion, rapid breathing, rapid heart rate, or extreme fatigue, and your temperature reads low, that combination warrants urgent attention. The absence of fever doesn’t mean the absence of infection.
Other Contributing Factors
Not eating enough can lower body temperature. Your body generates heat as a byproduct of digesting and metabolizing food, so prolonged calorie restriction or skipping meals reduces that heat output. People with eating disorders frequently report feeling cold and may have chronically low readings.
Blood sugar drops can also pull temperature down. When your blood sugar falls, your body has less readily available fuel to burn for warmth. This is worth noting if you have diabetes and take insulin or other glucose-lowering medications.
Dehydration, prolonged inactivity, and cold environments are the simpler explanations. If you’ve been sitting still in an air-conditioned room without eating or drinking much, a reading of 96.8°F might just reflect your circumstances rather than an underlying problem.
When Low Temperature Matters
Clinical hypothermia begins at 95°F (35°C). At that threshold, the body starts losing its ability to warm itself effectively. Mild hypothermia ranges from 90°F to 95°F, moderate from about 82°F to 90°F, and severe hypothermia falls below 82°F. These are medical emergencies tied to cold exposure, not the kind of low readings most people are noticing at home.
For readings that hover in the 96°F to 97°F range without an obvious environmental cause, the question is whether you have other symptoms. Persistent fatigue, unexplained weight changes, cold intolerance, hair thinning, or unusual weakness alongside a low temperature pattern suggests something metabolic is going on. A simple blood panel checking thyroid function and iron levels can rule out the most common culprits.