Body temperature gradually decreases as you age. Research from Stanford Medicine found that temperatures “decreased with age,” with today’s average adult body temperature hovering around 97.9°F rather than the long-cited 98.6°F standard. But the story goes well beyond a slightly lower number on a thermometer. Aging changes how your body produces heat, how it sheds heat, and how accurately it detects temperature threats, all of which carry real health implications.
How Babies and Children Regulate Temperature
Newborns enter the world with a unique heating system: brown adipose tissue, a specialized fat that generates warmth without shivering. When a baby is exposed to cold, the nervous system signals this brown fat to burn energy and produce heat, a process called non-shivering thermogenesis. This mechanism is critical during the first 36 hours of life, when newborns are most vulnerable to heat loss. Premature babies born before 30 weeks often lack enough brown fat to mount this response effectively, which is one reason neonatal units keep such tight control over ambient temperature.
Infants also run slightly warmer than adults. A rectal reading up to 100.4°F (38°C) falls within the normal range for a young child, compared to an oral ceiling of about 99.5°F (37.5°F) in adults. Children’s higher metabolic rate relative to body size, combined with a larger surface-area-to-weight ratio, means their core temperature fluctuates more easily. A toddler can spike a fever quickly but also lose heat to a cold environment faster than an adult would.
What Changes in Adulthood
Basal metabolic rate, the energy your body burns at rest to keep organs running, represents 60% to 80% of your total energy expenditure. It is also the primary engine of internal heat production. Starting in early adulthood, this rate drops by roughly 1% to 2% per decade. The decline is modest at first, but it compounds. By your 60s or 70s, your body is generating measurably less heat at rest than it did in your 20s.
Your daily temperature rhythm also shifts. Core body temperature follows a circadian cycle, dipping in the early morning and peaking in the late afternoon. In older adults, the amplitude of this cycle shrinks, the peak arrives earlier in the day, and the pattern becomes less stable overall. This flattened rhythm is one reason older adults may feel cold in the evening when younger people still feel comfortable.
Menopause and the Thermoneutral Zone
Menopause introduces a distinct disruption to temperature regulation that affects roughly 75% of women during the transition. The underlying mechanism involves the thermoneutral zone, the range of core body temperatures your brain considers “normal” and leaves alone. In premenopausal women, this zone is relatively wide, so minor fluctuations in core temperature don’t trigger a response. When estrogen levels drop at menopause, the thermoneutral zone narrows dramatically. Elevated brain norepinephrine, a stress-related chemical messenger, contributes to this narrowing.
The practical result: even a tiny rise in core temperature can cross the upper threshold and trigger a full-blown heat dissipation response, meaning flushing, sweating, and peripheral vasodilation. That’s a hot flash. It is not a malfunction but an exaggerated cooling response fired off by a brain that has become hypersensitive to small temperature shifts. Estrogen therapy works by raising the sweating threshold back up, widening the thermoneutral zone so those small fluctuations no longer set off alarms.
Why Older Adults Run Cooler
Several converging changes push baseline body temperature lower in people over 65. The subcutaneous fat layer beneath the skin, which acts as insulation, thins with age. Blood vessels lose elasticity, reducing the efficiency of circulation. Since blood absorbs and distributes heat throughout the body, sluggish circulation means less warmth reaches your extremities and skin surface. Meanwhile, the 1% to 2% per decade decline in metabolic rate means less internal heat is being produced in the first place.
Sweat glands change too, but in a way that affects cooling rather than warming. Older adults show a delayed onset of sweating and produce less sweat per gland during heat exposure. The total number of active sweat glands stays roughly the same. The issue is output per gland, likely due to structural shrinkage of the glands themselves and reduced sensitivity to the chemical signals that activate them. During exercise in hot environments, older adults consistently produce less sweat than younger adults at comparable exertion levels, making overheating a real risk.
On the cold side, the blood vessel response is equally compromised. When young skin detects cold, nerve signals trigger blood vessels to constrict, keeping warm blood in the body’s core. In older adults, this cold-triggered nerve activity is reduced by about 60% compared to younger people. One of the two chemical pathways responsible for this constriction disappears entirely with age, and the remaining pathway works less effectively. The result is that aged skin lets more blood flow to the surface during cold exposure, losing heat when it should be conserving it. People over 65 account for half of all cold-exposure deaths each year.
The Blunted Fever Problem
One of the most clinically significant consequences of lower baseline temperature in older adults is a weakened fever response. Fever is the body’s primary alarm system during infection, and it works less reliably with age. In a study of nursing home residents with confirmed infections, 47% never reached 101°F, the temperature traditionally used to define a significant fever. Their immune systems were fighting real infections, but the thermometer didn’t reflect it.
The reason is partly mathematical. If your baseline temperature sits at 97°F instead of 98.6°F, you need a larger absolute rise to cross 101°F. About one-quarter of those “blunted” fever episodes actually involved a temperature increase of 2.4°F or more from the person’s baseline, a meaningful immune response that simply didn’t reach the conventional fever cutoff. This is why geriatric guidelines suggest using a lower threshold, around 99°F or 100°F, and paying attention to any change of more than 2.4°F from a person’s known baseline. If you’re caring for an older adult, knowing their usual resting temperature matters more than memorizing a single “normal” number.
Reduced Cold Awareness
Beyond the physiological changes, older adults also lose some ability to sense that they’re getting cold. The nervous system’s thermal sensors become less responsive, so the subjective feeling of “I need to warm up” arrives later than it should. This creates a dangerous gap: the body is losing heat faster (due to thinner skin fat and impaired vasoconstriction) while simultaneously being slower to recognize the problem. Accidental hypothermia can develop in an older person at indoor temperatures that would feel merely cool to a younger adult, particularly in poorly heated homes during winter.
Heat awareness can also be dulled. Because the sweating response is delayed and the cardiovascular system is less able to shunt blood to the skin for cooling, older adults exercising or working outdoors in warm weather can overheat before they realize they’re in trouble. Healthy young men can increase skin blood flow by about 5.8 liters per minute during extreme heat exposure. Healthy older men manage only about 2.7 liters per minute, roughly half. That gap represents a significantly reduced ability to dump excess heat.
Practical Temperature Differences by Life Stage
Pulling this together, the trajectory looks like this: newborns and young children run slightly warm, with a broader normal range and more volatile swings. Healthy younger adults settle into the mid-97s to low-98s as a true average (not the old 98.6°F standard). From middle age onward, baseline temperature drifts lower, circadian swings flatten, and the body becomes less effective at both heating and cooling itself. By older adulthood, a resting oral temperature in the low 97s or even high 96s can be perfectly normal for that individual.
Where you measure also matters at any age. Rectal readings run highest (97.9°F to 100.4°F normal range), ear measurements are slightly lower, oral readings lower still, and armpit readings are the coolest and least precise (94.5°F to 99.1°F). These differences become especially important when evaluating an older person for fever, since an armpit reading of 99°F might actually represent a significant temperature spike for someone whose baseline sits near 96°F by that method.