A body temperature below the traditional 98.6 °F (37 °C) is usually harmless and, for many people, completely normal. The old textbook number was established in the 1800s, and research shows that average human body temperature has been steadily declining since then. That said, a reading below about 95 °F (35 °C) crosses into hypothermia territory and can signal a medical problem worth investigating, from thyroid disorders and blood sugar crashes to medication side effects and serious infections.
Your Thermometer Might Be the Real Issue
Before assuming your body is running cold, consider how you took the reading. The route matters enormously. An emergency department study comparing oral and rectal temperatures found the average oral reading was about 1.1 °F lower than rectal, with individual oral readings sometimes undershooting by nearly 3 °F.1PubMed Central. Oral and Tympanic Membrane Temperatures Are Inaccurate to Identify Fever in Emergency Department Adults A separate study of digital oral thermometers found they missed fever in about half of patients who actually had one, with oral readings averaging nearly two degrees cooler than rectal temperatures.2PubMed Central. Are Digital Oral Thermometer Readings Accurate in Adult Emergency Department Patients? Ear (tympanic) thermometers are similarly unreliable, with individual readings swinging widely in both directions compared to core body temperature.
Drinking cold water, breathing through your mouth, or not keeping the thermometer under your tongue long enough can all drag a reading down. Forehead and temporal artery scanners, popular since the pandemic, are convenient but sensitive to ambient temperature and skin moisture. If you consistently get readings that seem oddly low, try measuring again after sitting quietly for ten minutes with your mouth closed and nothing to eat or drink for 15 minutes beforehand. And if the reading still seems off, rectal temperature remains the clinical gold standard for accuracy, even if nobody’s favorite option at home.
98.6 Is Not Really Normal Anymore
The 98.6 °F benchmark dates back to a massive study by the German physician Carl Wunderlich in 1868. It stuck for over a century. But a large analysis spanning nearly two hundred years of birth cohorts found that average body temperature has dropped about 0.03 °C per decade, totaling roughly 0.6 °C (about 1 °F) in men born in the early 1800s compared to those born in the late 1990s, with a similar decline in women.3eLife. Decreasing human body temperature in the United States since the Industrial Revolution The reasons are still debated, but lower rates of chronic infection, better nutrition, climate-controlled environments, and reduced chronic inflammation all probably play a role. The upshot: a reading of 97.5 °F or even 97.0 °F may simply be your normal baseline, not a sign of anything wrong.
This matters because people who run cool at baseline can panic over a perfectly healthy reading. It also means that when you do get sick, your “fever” might not look like one on a thermometer. If your normal sits around 97.3 °F, a jump to 99.0 °F represents about the same internal shift as going from 98.6 to 100.3 in someone with a classic baseline. Knowing your own resting temperature, taken at the same time of day over several mornings, gives you a much better reference point than a number from an 1868 textbook.
How Age Affects Body Temperature
Older adults tend to run cooler than younger people, and this is well-documented. The thermoregulatory systems that maintain body temperature rely on almost every organ system, including the cardiovascular and respiratory systems, and these naturally lose efficiency with age.4PubMed. Age-dependent changes in temperature regulation – a mini review Reduced muscle mass, thinner skin, less subcutaneous fat, and decreased metabolic rate all contribute. The practical concern is that an older person with a serious infection might not spike a fever the way a younger person would, making infections easier to miss. Their tolerance for temperature extremes, both hot and cold, is also narrower.5PubMed Central. Aging and Thermoregulatory Control: The Clinical Implications of Exercising under Heat Stress in Older Individuals
The opposite end of the age spectrum has its own risks. Newborns lose heat rapidly because of their large surface-area-to-body-mass ratio, thin skin, limited subcutaneous fat, high body water content, and immature metabolic mechanisms.6PubMed Central. Neonatal Hypothermia and Associated Factors among Newborns Admitted in the Neonatal Intensive Care Unit of Dessie Referral Hospital, Amhara Region, Northeast Ethiopia A newborn in a cool room can become hypothermic far more quickly than an adult, which is why hospitals are meticulous about skin-to-skin contact and warming immediately after birth. If your infant feels cool to the touch or has a temperature below about 97.7 °F (36.5 °C), that warrants prompt medical attention.
Body Composition and Muscle Mass
Your body generates heat primarily through metabolic activity, and skeletal muscle is the single largest contributor to your basal metabolic rate.7PubMed Central. Skeletal Muscle Thermogenesis and Its Role in Whole Body Energy Metabolism People with less muscle mass simply produce less heat at rest. This is part of why women, who on average carry less skeletal muscle than men, tend to report feeling cold more often. It also helps explain why very thin or underweight individuals frequently have lower baseline temperatures.
A study examining body temperature in older adults found that those in the lower-temperature group had lower body mass index and less body fat, and the researchers noted that reduced brown adipose tissue (the type of fat that generates heat) could be a contributing factor.8PubMed Central. Effect of Exercise Training on Body Temperature in the Elderly: A Retrospective Cohort Study So if you’re lean, small-framed, or have recently lost significant weight, a slightly lower temperature is an expected consequence, not necessarily a medical concern.
Underrating and Eating Disorders
Severe calorie restriction can drive body temperature down meaningfully. In anorexia nervosa, patients have significantly lower core temperatures compared to healthy controls, and this reflects a genuine metabolic slowdown, not just feeling chilly.9PubMed Central. The Central Role of Hypothermia and Hyperactivity in Anorexia Nervosa: A Hypothesis The mechanism is straightforward: when the body doesn’t receive enough fuel, it throttles back its resting energy expenditure to conserve resources. One study measured resting energy expenditure in patients with anorexia nervosa and found it was significantly suppressed compared to what would be predicted by their body size, averaging roughly 850 calories per day versus an expected 1,080.10PubMed Central. Chronic starvation secondary to anorexia nervosa is associated with an adaptive suppression of resting energy expenditure
This isn’t limited to diagnosed eating disorders. Crash diets, prolonged fasting, or simply not eating enough over weeks and months can produce the same thermoregulatory suppression. If you’ve noticed you’re always cold and you’ve also been eating less than usual, the two are almost certainly connected. Your body is doing exactly what evolution designed it to do: conserve energy by running cooler.
Thyroid Problems
The thyroid gland sets the pace for your metabolism, and when it underperforms, virtually everything slows down, including heat production. Hypothyroidism is probably the single most common medical condition people associate with feeling cold, and they’re right to. An underactive thyroid reduces your basal metabolic rate, which means less heat generated at rest. The constellation of symptoms is distinctive: fatigue, weight gain, dry skin, constipation, and persistent cold intolerance. In severe, untreated cases (myxedema coma, which is a medical emergency), core body temperature can drop dangerously low.
The good news is that thyroid function is easy to check with a simple blood test, and hypothyroidism responds well to replacement hormone therapy. If your low temperature is accompanied by any of the symptoms above, a thyroid panel is a reasonable first step. Other hormonal issues can play a role too. Adrenal insufficiency and low cortisol states both impair the body’s ability to maintain temperature, though these are less common than thyroid disease.
Medications That Can Push Your Temperature Down
Several classes of medication can interfere with thermoregulation, and this side effect is underrecognized by both patients and clinicians. Antipsychotic drugs are among the most studied culprits. A systematic review of hypothermia linked to antipsychotic use found that the mechanism likely involves two things: peripheral blood vessel dilation (which dumps heat into the environment) and disruption of the brain’s central temperature-control system.11PubMed Central. Hypothermia due to Antipsychotic Medication: A Systematic Review Drugs that block alpha-adrenergic receptors, including chlorpromazine, risperidone, and clozapine, are particularly likely to cause this problem because those receptors help constrict blood vessels in response to cold.
Antipsychotics aren’t alone. Sedatives, opioids, and general anesthetics can all suppress the shivering response and blunt temperature regulation. Some blood pressure medications that dilate blood vessels can have a mild cooling effect. If you started a new medication and noticed you’re running cooler than usual, it’s worth checking the prescribing information or asking your pharmacist. The effect is usually mild in healthy adults at room temperature, but it can become dangerous if combined with cold exposure, alcohol, or other risk factors.
Blood Sugar Crashes
Hypoglycemia, a sharp drop in blood sugar, can occasionally cause hypothermia, although most people associate low blood sugar with shakiness and sweating rather than a falling temperature. A documented case illustrated this clearly: a hospitalized patient whose blood sugar dropped overnight developed progressive hypothermia that didn’t respond to warming blankets, but resolved promptly once his blood sugar was corrected with a dextrose infusion.12PubMed Central. Hypothermia as a forgotten sign of prolonged severe hypoglycaemia The mechanism makes intuitive sense: glucose is the fuel your cells burn to produce heat, and when there isn’t enough of it, heat production falls.
This is most relevant for people with diabetes who use insulin or sulfonylurea medications, because they’re the ones most likely to experience prolonged, severe low blood sugar. But it can also happen in people who skip meals for an extended period or binge-drink alcohol on an empty stomach (alcohol impairs the liver’s ability to release stored glucose). If you find yourself both shaky and unusually cold, checking your blood sugar is a smart move.
Infections and Sepsis
Most people expect infections to cause fever, and usually they do. But a subset of patients, particularly those with severe infections, actually become hypothermic instead. This paradoxical response is a warning sign, not a reassurance. In critically ill patients with sepsis, hypothermia was associated with dramatically worse outcomes. One large database study found that patients with sepsis who presented with hypothermia had a 28-day mortality rate of about 54%, compared with roughly 19% in those who were febrile.13PubMed Central. Association between body temperature and all-cause mortality in patients with sepsis: analysis of the MIMIC-IV database Another study confirmed the link, finding that hypothermia in sepsis was independently associated with nearly twice the odds of death at 180 days even after accounting for other variables.14Scientific Reports. Hypothermia association with all-cause mortality in critically ill patients with sepsis based on the MIMIC-IV database
Why does this happen? When the immune system mounts a massive response and the body’s resources become overwhelmed, its ability to generate and maintain heat can collapse. Older adults, immunocompromised individuals, and very young children are more likely to respond to infection with hypothermia rather than fever. This is particularly treacherous because caregivers may see the lack of fever as a reassuring sign when it’s actually the opposite. If someone is clearly unwell with signs of infection, including confusion, rapid heart rate, low blood pressure, or mottled skin, a low temperature reading should raise alarms rather than provide comfort.
Kidney Disease and Uremia
Advanced chronic kidney disease can disrupt thermoregulation through a mechanism distinct from other causes. When the kidneys fail, waste products accumulate in the blood (a condition called uremia), and some of those waste products appear to act as natural cooling agents. They can trigger blood vessel dilation at the skin surface and suppress the shivering reflex, both of which work against heat retention.15PubMed Central. Profound Hypothermia as a Rare Presentation of Uremic Syndrome in a Patient With Advanced Chronic Kidney Disease: A Case Report and Literature Review In at least one well-documented case, a patient’s hypothermia resolved after starting dialysis, which supports the idea that the accumulation of uremic toxins was directly responsible.
This is a rare presentation, so it shouldn’t be high on your worry list if you have no history of kidney problems. But if you already know you have chronic kidney disease and notice your temperature trending downward, it’s worth mentioning to your nephrologist as a possible sign that your kidney function has worsened.
Brain and Hypothalamic Causes
The hypothalamus acts as the body’s thermostat, and anything that damages or compresses it can throw temperature regulation off. A striking case report described a patient who developed recurring episodes of spontaneous hypothermia caused by a large skull base tumor (meningioma) pushing against the hypothalamus.16PubMed Central. Acquired spontaneous periodic hypothermia and pancytopenia secondary to hypothalamic compression from a large skull base meningioma The patient also showed signs of disrupted hormonal function from the hypothalamic-pituitary axis being compressed. Once infection and adrenal insufficiency were ruled out, the tumor compression was identified as the cause.
Strokes, traumatic brain injuries, and inflammatory conditions affecting the brain can produce similar thermoregulatory disruption. These are uncommon causes, but they tend to produce a pattern that’s hard to miss: episodic temperature drops with no obvious environmental trigger, often accompanied by other neurological symptoms. If your temperature repeatedly drops below 95 °F in a warm environment without any clear reason, a neurological evaluation might be appropriate.
Environmental Exposure and Alcohol
The most intuitive reason for low body temperature is simple cold exposure. Your body loses heat faster than it can produce it when you’re inadequately dressed in cold weather, immersed in cold water, or stuck in a cold environment for an extended period. Wind and moisture accelerate heat loss dramatically. Mild hypothermia (temperatures in the 90–95 °F range) causes shivering, clumsiness, and confused thinking. Below 90 °F, the situation becomes life-threatening, as the heart becomes prone to dangerous rhythm disturbances.
Alcohol complicates this picture in a deceptive way. Drinking makes you feel warmer by dilating blood vessels near the skin surface, but this actually accelerates heat loss from your core. Alcohol also impairs judgment about when to come inside and blunts the shivering response. The combination of alcohol and cold exposure is a classic setup for accidental hypothermia, which is why a disproportionate number of hypothermia cases involve intoxication. If you’re going to be outdoors in cold weather, layering properly and staying dry matter far more than having a drink to “warm up.”
When a Low Reading Actually Warrants Concern
Most people who check their temperature and get a reading of 97-something have nothing to worry about. The threshold where concern becomes appropriate depends on context more than a single number. As a rough guide, readings below 95 °F (35 °C) taken properly are considered hypothermic and deserve medical attention regardless of the cause. But even readings in the 95–97 °F range can be significant if they come with other symptoms.
Situations that warrant a call to your doctor or a trip to urgent care include:
- Infection signs plus low temperature: Confusion, rapid breathing, fast heart rate, or low blood pressure alongside a low reading, especially in an older adult, could indicate sepsis.
- Persistent cold intolerance with fatigue: A pattern of always feeling cold combined with weight gain, dry skin, and exhaustion suggests hypothyroidism worth testing for.
- New medication and new symptoms: A temperature drop that began shortly after starting an antipsychotic, sedative, or opioid should be reported to the prescribing clinician.
- Known chronic illness: If you have diabetes, kidney disease, or an eating disorder and notice a falling temperature trend, the underlying condition may be worsening.
- Unexplained, recurring drops: Temperature repeatedly dipping below 95 °F in a warm environment without an obvious cause, particularly with headaches or hormonal changes, justifies further investigation.
For everyone else, the most useful thing you can do is establish your personal baseline. Take your temperature at the same time each morning for a week or two using the same thermometer and method. That number, whatever it is, becomes your reference point. A temporary dip after being outside in cold weather or sitting in an air-conditioned office all day is meaningless. A sustained change from your baseline, especially paired with new symptoms, is the signal that something might deserve a closer look.