Alternating between feeling hot and cold usually means your body’s internal thermostat is actively resetting, whether because of infection, hormonal shifts, stress, or simply the time of day. Your nervous system constantly adjusts heat production and heat loss to keep your core temperature within a narrow range, and when something disrupts that balance, you can swing from shivering to sweating in minutes. The causes range from completely harmless to medically serious, and the pattern of your symptoms often points toward the explanation.
How Your Body Keeps Its Temperature Stable
Your brain’s hypothalamus acts as a thermostat. Temperature-sensing cells throughout your skin and organs feed information to this region, and it coordinates a response: widening blood vessels and triggering sweat when you’re too warm, constricting blood vessels and activating shivering or other heat-producing mechanisms when you’re too cool.1Europe PMC. Regulation of Body Temperature by the Nervous System This system works well under normal conditions, but it can be thrown off by a surprisingly long list of triggers. When the set point shifts, or when competing signals confuse the system, you get that disorienting cycle of feeling hot then cold.
One factor people rarely consider is that your body also has a built-in heat-generation organ: brown adipose tissue, sometimes called brown fat. Unlike regular fat, brown fat burns calories specifically to produce warmth. When you’re exposed to cold, your sympathetic nervous system activates brown fat almost immediately to help maintain temperature without shivering.2Europe PMC. Brown fat thermogenesis and cold adaptation in humans If this system overreacts or underreacts, you feel the mismatch as unexpected chills or warmth.
Fever and the Classic Hot-Cold Cycle
The most common reason people alternate between hot and cold is a fever, and the mechanism is more interesting than most people realize. During an infection, your immune system releases signaling molecules that ultimately cause prostaglandin E2 to act on receptors in the hypothalamus. This raises the thermostat’s set point, sometimes by a full degree or more.3PubMed Central. Fever Is Mediated by Conversion of Endocannabinoid 2-Arachidonoylglycerol to Prostaglandin E2 Your brain now “thinks” your normal temperature is too low, so it triggers chills, shivering, and a drive to bundle up under blankets. Once your body has generated enough heat to reach the new, higher set point, you feel hot. When the fever breaks, the set point drops back down, and your body switches to cooling mode: sweating, flushed skin, kicking off the blankets.
This is why chills at the start of an illness and drenching sweats as the fever resolves are really two sides of the same process. Your body isn’t malfunctioning; it’s executing a deliberate defense strategy. Animal research has even shown that biphasic fevers, those with two distinct peaks, involve different behavioral phases. The initial rise is associated with increased activity and alertness, while the second phase tends to bring fatigue and stillness, almost as if the body shifts from an active fighting response to a conserving one.4ResearchGate / Annals of the New York Academy of Sciences. The Two Phases of Biphasic Fever? Two Different Strategies for Fighting Infection?
Hormonal Shifts and Hot Flashes
If you’re going through perimenopause or menopause, you probably don’t need anyone to explain what a hot flash feels like. But the mechanism behind it is worth understanding, because it explains why these episodes often involve both heat and cold. Hot flashes are essentially a heat-dumping response triggered by tiny increases in core body temperature. In people with adequate estrogen, the body tolerates a wide range of slight temperature fluctuations without reacting. In estrogen-depleted states, that “thermoneutral zone” narrows dramatically. A rise of just a fraction of a degree can trigger profuse sweating and skin flushing, followed by chills as the body overcools in response.5Europe PMC / Elsevier. Menopausal hot flashes: mechanisms, endocrinology, treatment
The narrowing of this zone is partly caused by elevated sympathetic nervous system activity, mediated through specific adrenergic receptors, rather than estrogen loss alone.5Europe PMC / Elsevier. Menopausal hot flashes: mechanisms, endocrinology, treatment That’s why stress, alcohol, and warm rooms reliably make hot flashes worse: they all raise sympathetic tone or nudge core temperature upward just enough to cross that shrunken threshold. It also explains why some people who take estrogen therapy still get hot flashes. The hormonal piece matters, but it isn’t the whole story.
Thyroid Problems
Your thyroid gland is essentially the dial on your metabolic furnace. Thyroid hormones increase heat production across almost every tissue in your body by ramping up energy use. They also interact with the sympathetic nervous system to fine-tune heat generation in response to cold.6PubMed. Thyroid hormone control of thermogenesis and energy balance When thyroid levels are too high, as in hyperthyroidism, you tend to feel warm, sweat easily, and become intolerant of heat. When they’re too low, as in hypothyroidism, you run cold, have trouble warming up, and may shiver more easily.
What catches people off guard is that thyroid conditions can fluctuate, especially early in autoimmune thyroid disease. You might swing between overproduction and underproduction before settling into one pattern. During these swings, feeling hot one week and cold the next makes perfect sense physiologically. If you’ve noticed persistent, unexplained temperature sensitivity in either direction, a simple blood test can check thyroid function.
Stress, Anxiety, and Psychogenic Fever
Stress doesn’t just make you feel warm; it can measurably raise your body temperature. Acute psychological stress triggers the sympathetic nervous system to activate heat production through brown adipose tissue, the same mechanism the body uses to warm up in cold weather. This process is distinct from infection-driven fever because it doesn’t involve the inflammatory signaling molecules that infections use.7PubMed Central. Psychogenic fever: how psychological stress affects body temperature in the clinical population The result is a genuine, measurable temperature increase, sometimes high enough to register on a thermometer, that resolves when the stress passes.
For people with chronic stress or anxiety disorders, the picture gets more complicated. Ongoing low-grade activation of the sympathetic nervous system can keep body temperature slightly elevated, and the autonomic instability that comes with anxiety often produces waves of feeling hot (flushing, sweating) followed by feeling cold (chills, goosebumps). If you’ve noticed that your hot-cold episodes track with stressful situations, anxious thoughts, or panic attacks rather than illness, this is a likely explanation. Anti-inflammatory medications like ibuprofen won’t help with psychogenic fever, because inflammation isn’t driving it.
Your Daily Temperature Rhythm
Even without any illness or hormonal issue, your body temperature naturally rises and falls by about half a degree Celsius over the course of a day. This isn’t just a side effect of being more active during the day and resting at night. Your circadian clock actively modulates how much metabolic heat your body produces, creating a genuine temperature rhythm that persists even if you stay in bed all day.8Europe PMC. Circadian rhythmicity of body temperature and metabolism Temperature typically bottoms out in the early morning hours and peaks in the late afternoon or early evening.
This matters because people who are already on the edge of feeling uncomfortable, due to a mild illness, hormonal changes, or a warm bedroom, tend to notice these natural swings. You might feel fine during the day and then oddly chilly at 3 a.m., or uncomfortably warm by evening. You’re not imagining it, and it doesn’t necessarily mean something is wrong. Your body is simply riding its normal temperature wave, and whatever else is going on is making the peaks and troughs more noticeable.
What Happens During Sleep
Sleep itself changes how your body handles temperature. As you fall asleep, your core temperature drops, partly because your body deliberately shunts heat to your skin (which is why warm hands and feet help you fall asleep faster). During deep sleep, your body still thermoregulates, but during REM sleep, the rules change. Sweating responses become blunted, and in animal studies, temperature regulation during REM sleep is essentially suspended.9PubMed Central. Sleep and thermoregulation Some researchers describe REM sleep as a period of transient heterothermy, meaning your body temporarily behaves more like a cold-blooded animal, drifting toward whatever the ambient temperature is.10PubMed Central. REM Sleep and Endothermy: Potential Sites and Mechanism of a Reciprocal Interference
This is one reason you might wake up sweating or shivering in the middle of the night even when the room temperature hasn’t changed. If you woke from a REM cycle in a slightly warm room, you may have been accumulating heat without your normal cooling responses kicking in. The reverse happens in cool rooms. Night sweats that follow this pattern and occur without other symptoms are often just a quirk of sleep physiology rather than a sign of disease.
After Exercise
A hard workout raises your core temperature considerably, sometimes by a full degree or more. As you cool down afterward, the process isn’t always smooth. Your body may overshoot the cooling response, leaving you feeling cold even in a room that felt comfortable before you started exercising. Research on cold-sensitive individuals has shown that cold sensations after exercise can persist for half an hour or longer, especially in the extremities, and are more pronounced when the ambient temperature is even slightly cool.11Wiley Online Library (Physiological Reports). Body temperature and cold sensation during and following exercise under temperate room conditions in cold‐sensitive young trained females
The takeaway here is simple: if you feel warm during exercise and then chilly for a while afterward, that’s your thermoregulatory system doing its job. The discomfort is real, but it doesn’t indicate a problem. Changing into dry clothes and staying in a moderately warm environment after exercise can smooth out the transition.
Alcohol and Temperature Perception
Alcohol famously makes you feel warm, and it does so by dilating blood vessels in your skin. That sends a rush of warm blood to the surface, which you perceive as a pleasant warmth. But that same process accelerates heat loss from your core. Research has shown that after drinking, skin blood flow and sweat rate increase within about ten minutes, and deep body temperature subsequently drops, falling roughly 0.3°C below what it would be without alcohol.12Elsevier / PubMed Central. Effects of alcohol on thermoregulation during mild heat exposure in humans The result is a familiar pattern: feeling pleasantly warm right after drinking, then unexpectedly cold an hour or two later as your core temperature slides.
Alcohol withdrawal presents an even more dramatic version of this. The increased sympathetic nervous system activity that accompanies withdrawal can produce intense sweating, fever, and chills, sometimes severe enough to cause significant fluid loss and medical complications.13PubMed Central. Severe diaphoresis and fever during alcohol withdrawal cause hypovolemic shock: case report If you experience pronounced hot-cold cycling during or after heavy drinking, it’s worth recognizing this as more than discomfort.
Medications That Disrupt Temperature
A number of medications can push your temperature in one direction or both. Some drugs increase heat production, some impair sweating, and some do both simultaneously. Drug-induced hyperthermia covers a range of potentially dangerous syndromes that share the common feature of pharmacological agents overriding the body’s normal thermoregulatory controls.14Clinical Critical Care. Understanding drug-induced hyperthermia Common culprits include:
- SSRIs and SNRIs: Antidepressants in these classes can cause excessive sweating in some people, and in rare cases can contribute to serotonin syndrome, which involves dangerously high temperatures.
- Anticholinergics: Medications with anticholinergic effects, including certain antihistamines, bladder drugs, and older antidepressants, can impair sweating and lead to overheating.
- Stimulants: Amphetamines, cocaine, and some ADHD medications increase metabolic heat production.
- Opioids: Can disrupt the hypothalamic set point, and opioid withdrawal commonly produces chills and sweating.
If your hot-cold episodes started or worsened after beginning a new medication, that’s a conversation worth having with your prescriber. Temperature-related drug effects are underappreciated and often fixable with dose adjustments or alternatives.
Aging and Temperature Sensitivity
Older adults tend to run cooler than younger people, and they tolerate temperature extremes less well. This isn’t because of one failing system; it’s because thermoregulation relies on the cardiovascular system, the respiratory system, metabolic pathways, and the nervous system all working together, and each of these degrades somewhat with age.15Karger Publishers (Gerontology). Age-dependent changes in temperature regulation – a mini review Blood vessels may not dilate or constrict as quickly, sweating may be less efficient, and the metabolic furnace may produce less heat at baseline.
The practical effect is that older adults are more likely to feel cold in mildly cool environments and more vulnerable to overheating on warm days. They may also be less aware that they’re overheating, because the subjective sensation of warmth can lag behind the actual temperature rise. If you’re caring for an older family member, ambient temperature matters more than you might think, and the person’s own reports of comfort may understate the problem.
Vascular Conditions and Localized Temperature Changes
Sometimes the hot-cold sensation isn’t happening all over your body. It’s localized to your hands, feet, or specific patches of skin. Raynaud’s phenomenon is a classic example. In Raynaud’s, blood vessels in the fingers and toes spasm in response to cold or stress, producing a distinctive color sequence: white as blood flow is cut off, blue as oxygen is depleted, and then red as blood returns with a rush of warmth and sometimes burning pain.16BMJ Case Reports. Mottled Raynaud’s phenomenon and hand-arm vibration syndrome: followed up for 10 years The affected digits feel intensely cold, then uncomfortably hot, sometimes within minutes.
Raynaud’s can exist on its own or as part of an autoimmune condition. If your hot-cold cycling is mainly in your extremities and follows the white-blue-red pattern, it’s worth bringing up with a doctor, especially if it’s accompanied by numbness or tingling. The condition is manageable but can worsen over time if left unaddressed.
When Alternating Temperature Is a Warning Sign
Most causes of feeling hot then cold are benign or self-limiting. But there are situations where the pattern signals something serious. In sepsis, the body’s response to overwhelming infection, temperature dysregulation is a hallmark. Some patients spike high fevers while others become hypothermic, and both patterns are associated with poor outcomes.17Europe PMC. Temperature control in sepsis If your temperature fluctuations are accompanied by confusion, rapid heart rate, very low blood pressure, or severe illness, that’s an emergency, not a thermoregulation curiosity.
Other red flags worth knowing about: drenching night sweats that soak your sheets repeatedly (which can indicate infections like tuberculosis or certain cancers, particularly lymphomas), unexplained fevers lasting more than a couple of weeks, and temperature instability following a head injury (which can damage the hypothalamus directly). These scenarios represent a small fraction of the reasons people experience hot-cold cycling, but they’re the ones that benefit from prompt medical evaluation rather than reassurance.
Why Some People Are Just “Temperature Sensitive”
After ruling out medical causes, some people simply have a thermoregulatory system that’s more reactive than average. They feel cold when others are comfortable, overheat in mildly warm rooms, or swing between the two throughout the day. This individual variation is real and has biological underpinnings. The amount of brown fat you carry, how efficiently your blood vessels respond, your body composition, your hormonal balance, and even your habitual cold exposure all influence how tightly your temperature stays controlled and how much you notice when it shifts. People who regularly expose themselves to cold gradually increase their brown fat activity, which improves their cold tolerance over time.2Europe PMC. Brown fat thermogenesis and cold adaptation in humans
If you’re someone who has always been more sensitive to temperature than the people around you, there’s a decent chance nothing is wrong. Your thermostat is just set with tighter tolerances, reacting more vigorously to smaller changes. Dressing in layers, managing room temperature actively, and paying attention to triggers like stress, caffeine, and alcohol can go a long way toward smoothing out the experience.